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A Site Conditions Map for California Based on Geology and Shear Wave Velocity
Abstract
One simple way of accounting for site conditions in calculating seismic hazards is to use the shear-wave velocity in the shallow subsurface to classify materials. The average shear-wave velocity to 30 m ( V 30s) has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions. We have prepared a site-category map of California by first classifying the geologic units shown on 1:250,000 scale geologic maps. Our classification of geologic units is based on V 30s measured in 556 profiles and geological similarities between units for which we have V s data and the vast majority of units for which we have no data. We then digitized the geologic boundaries from those maps that separated units with different site classifications.
V s data for California shows that several widespread geologic units have ranges of V 30s values that cross the boundaries between NEHRP-UBC site categories. The Franciscan Complex has V 30s values across UBC categories B and C with a mean value near the boundary between those two categories. Older alluvium and late Tertiary bedrock have V 30s values that range from about 300 to about 450 m/sec, across the boundary between categories C and D. To accommodate these units we have created intermediate categories, which we informally call BC and CD. Geologic units that have, or are interpreted to have, V 30s values near the boundary of the UBC categories are placed in these intermediate units.
In testing our map against the available V 30s measurements, we have found that 74% of the measured V 30s values fall within the range assigned to the V s category where they fall on the map. This ratio is quite good considering the inherent problems in plotting site-specific data on a regional map and the variability of physical properties in geologic units. We have also calculated the mean and distribution of V 30s for each of our map units and prepared composite profiles, showing the variation of V s in the upper 100 m from the available V s data. These data show that the map categories that we have defined based on geologic units have different V s properties that can be taken into account in calculating seismic hazards.
... A horizontal-to-vertical response spectral ratio (HVSR) method can be used to estimate the site condition for strong-motion stations (e.g., Yamazaki and Ansary, 1997;Zhao et al., 2006;Di Alessandro et al., 2012;Ghofrani and Atkinson, 2014). Commonly, for regional site classification, proxies such as topographic slope (Wald and Allen, 2007), geomorphometry (Yong et al., 2012;Yong, 2016;Iwahashi et al., 2018), geology (rock or sediment type and age) (Park and Elrick, 1998;Wills et al., 2000;Holzer et al., 2005;Wills and Clahan, 2006), or combinations of factors Thompson et al., 2014;Wills et al., 2015;Ahdi et al., 2017;Parker et al., 2017) are used. These proxies are developed statistically by correlating V S30 to the proxy parameters in areas where V S30 data are available. ...
... We use NEHRP site categories rather than the Chinese code standards, because the geological and geographical proxies for NEHRP classes were better constrained at present. We follow the geology-site condition associations of Park and Elrick (1998), Wills et al. (2000), Holzer et al. (2005), Wills and Clahan (2006), and Wills et al. (2015) and apply the associations to mainland China. For glacial deposits and loess, we apply the associations based on studies on Chinese loess (Wu et al., 2012) and late Quaternary geomorphology in the southeastern Tibetan plateau (Shi, 2002). ...
... ASCE (2016) specifies that if site category B is established without the use of on-site V S30 measurements (as is the case here because we use the geology proxy), then that category is considered to have an amplification equal to 1.0. Similarly, we lack the site-specific evaluations required to We follow the geology-site classification associations by Park and Elrick (1998), Wills et al. (2000), Shi (2002), Holzer et al. (2005), Wills and Clahan (2006), Wu et al. (2012), and Wills et al. (2015). We use the age, genesis, and lithologic descriptions of the units in the final geology and Quaternary maps to assign the NEHRP site categories to each geologic unit (Table 4). ...
We use geology as a proxy to produce a site condition map of mainland China for seismic hazard assessment. The geology is from a 1:1,000,000‐scale digital database and a 1:2,500,000‐scale Quaternary map. We use the lithological descriptions and ages to assign the site condition for each geologic unit. Published site condition data are used to evaluate our mapping results. Our results agree well for the strong‐motion stations in Gansu–Sichuan area, except in the mountainous area. There, the mismatches are due to our geological map scales missing narrow river terrace deposits. Our results also match well in the Shandong and Beijing Plain areas, except in thin fluvial and alluvial deposits fringing bedrock mountains. Our site‐response categories match well‐published average VS–depth profiles from microzonation studies of 14 major urban areas.
... Studies indicate that one of the essential factors in establishing seismic design criteria for the geotechnical earthquake engineering field is to measure the shear wave velocity (V S ). In such studies, shear wave velocities are coupled with the other physical properties of sediments assist in the determination of the dynamic properties of soils and rocks, along with the characterization of local geologic conditions [49][50][51][52][53][54]. Evaluations of local site conditions are reflected in seismic code provisions. ...
... By combining different constraints with the V S30 such as geological unit, topography, and slope gradient, a more consistent and welldistributed database for the seismic zonation map has been developed. In the literature, similar assessments have been mentioned by various researchers [48,50,51,67,68]. Regarding these studies, it can be inferred that systematic geomorphological (i.e., topography and slope gradient), geological, and geospatial data along with logical prediction variables can be used as a reasonable method for the estimation of the V S30 . ...
Assessment of potential seismic risk and losses in urban environments is necessary for several purposes ranging from risk mitigation to city and regional planning. It is well known that loss estimation should be performed within an interdisciplinary setting involving earth sciences and engineering. Field experience from recent events worldwide shows that the spatial variability of seismic damage is due to the combined effects of earthquake source properties, local site conditions and structural characteristics. In this study, a scenario-based multi-input damage estimation framework in an urban region was utilized for the Gaziantep city center (southeastern Turkey) that is located in a region of high seismic hazard with no large events in the instrumental era. Initially, a thorough geological and seismo-tectonic assessment of the area was performed followed by estimation of two critical scenario events with moment magnitude (Mw) of 6.5 and 6.6 on nearby active faults. Then, a regional velocity model was compiled from regressions of existing regional geotechnical and seismic data in terms of the VS30 parameter. As the next step, field surveys for the assessment and classification of buildings in the study area were performed followed by vulnerability analyses. As the last step, the mean damage ratios were computed at 198 neighborhoods within the city center. The results indicate not only a high hazard but also high risk in the Gaziantep area due to the combination of close proximity to the faults along with local site effects and building fragilities.
... In the last decades, there has been a revived interest in methods used to measure the shear wave velocity (V s ) due to the inclusion of the value up to 30 m depth (V s, 30 ) in several building codes [11][12][13][14][15]. Accordingly, several direct and indirect methods were developed to evaluate V s, 30 . ...
... The current investigation focuses on the wave propagation along the z axis corresponding to the position of the excitation source, when x = 0. The dispersion law of the coupled u-w wave originates by subtracting Equation (14) to Equation (15): ...
The estimate of the velocity of shear waves (Vs) is essential in seismic engineering to characterize the dynamic response of soils. There are various direct methods to estimate the Vs. The authors report the results of site characterization in Macerata (Italy), where they measured the Vs using the seismic dilatometer in a 100 m deep borehole. The standard V s estimation originates from the cross-correlation between the signals acquired by two geophones at increasing depths. This paper focuses on the estimate of the dependence of V s on the wavenumber. The dispersion curves reveal an unexpected hyperbolic dispersion curve typical of Lamb waves. Interestingly, the contribution of Lamb waves may be notable up to 100 m depth. The amplitude of surface waves decrease rapidly with depth; still, their influence may be essential up to depths considered unusual for standard geotechnical investigations, where their effect is generally neglected. Accordingly, these waves may bias the outcomes of the standard V s estimations, which ignore frequency-dependent phenomena. The paper proposes an enhancement of the accepted procedure to estimate V s and addresses the importance of Lamb waves in soil characterization.
... Although V S30 is a simplified index for the characterization of soil properties, it is impractical to conduct the requisite densely spaced direct measurements for large areas. Therefore, in terms of the applications to hazard mapping, earthquake fatality/loss impact estimation, earthquake insurance models, and so forth, which are designed to use at regional or even national scales, it is sometimes necessary to estimate V S30 through correlations with geological, geomorphologic, or topographic proxies (Wills et al., 2000;Wills and Clahan, 2006;Wald and Allen, 2007;Yong et al., 2012), or to estimate it from shallow borehole profiles (i.e., boreholes less than 30 m deep) at the same site (Boore, 2004;Boore et al., 2011;Dai et al., 2013;Midorikawa and Nogi, 2015;Wang and Wang, 2015). ...
... Tinsley and Fumal (1985) used the surficial geologic age and grain size to map V S in the Los Angeles region. Wills and his coworkers (Wills et al., 2000(Wills et al., , 2015Wills and Clahan, 2006) applied geologic units from the geologic map as predictors for V S30 in California. Li et al. (2019) considered the geologic age and grain size in developing a site classification map of China. ...
Employing extrapolation models to estimate the time-averaged shear-wave velocity to 30 m (VS30) from a shallow borehole profile is an effective way to expand the VS30 data volume and a necessary initial step for developing VS30 proxy models. Past extrapolation model studies have relied only on shallow borehole shear-wave velocity (VS) profiles to estimate VS30. In this study, we enhance the model by accounting for additional parameters including location slope, geologic age, and geotechnical class. We first compile a new borehole profile database (BPDB) that contains information about 8831 boreholes in China. Using this BPDB, we analyze the VS characteristics of strata for various location slopes, geologic ages, and geotechnical classes. The result shows that the location slope and geologic age have significantly different effects on the VS characteristics, whereas the differences for sand, silt, and clay are small. We build a parameter classification scheme that classifies the location slope into six groups, the geologic age into seven hierarchical types, and the geotechnical class into four hierarchical types. This scheme ensures that each group/type has its distinctive VS characteristic. We evaluate five existing VS models and choose the model that shows the best performance on the BPDB as the “prototype” model. We classify the BPDB boreholes by the parameter classification scheme and use the form of “prototype” model to develop a parametrical model that consists of 33 single-parameter-value models. For a shallow borehole (<30 m), if its location slope, geologic age, or geotechnical class is available besides its VS profile, applying the parametrical model will get more accurate estimated VS30 and model uncertainty estimation than those of existing models that only utilize the information of the VS profile.
... However, it has long been recognized that the near-surface geology has a strong influence on seismic waves, amplifying (or deamplifying) their amplitudes and altering their frequency content (e.g. Anderson et al., 1996, Wills et al., 2000. Therefore, mapped variations in local geology within the JÖKULL No. 68, 2018 town ( Figure 3) are of great importance for the interpretation of recorded earthquake strong-motion effects on the ICEARRAY II stations (Halldorsson et al., 2012;Rahpeyma et al., 2017). ...
The Húsavík–Flatey Fault Zone (HFFZ) is one of the largest system of transform faults in Iceland on which damaging earthquakes have repeatedly taken place. The town of Húsavík on the coast of the Tjörnes peninsula lies in an extensional basin formed due to a slight bend in the HFFZ. The fault movement and geological processes have over time created considerable spatial variations in both the topography and shallow subsurface materials on which the town resides. As a result, the earthquake hazard varies significantly within the town, and therefore the local seismic risk as well. In this study, we expand on previous research by mapping the geomorphology of the Húsavík area. Namely, the geomorphology identifies the secondary processes that can be activated during strong earthquake motions and cause additional damage or loss. Through field inspection and remote sensing we have examined the predominant surface geological types and actual and potential geomorphic phenomena and processes in the Húsavík area. The results are presented as a set of geological and geomorphological maps outlining the types and classes of geomorphological processes, along with the topography and slope inclinations of Húsavík. The geomorphological characteristics of the Húsavík area are shown to be largely dominated by mass gravitational motion such as landslides and rockfalls, primarily on the Húsavík mountain and along the Botnsvatn incline, but also along the coastline of Húsavík, especially along the steep slopes in the southernmost part of town. We have also identified areas with possible liquefaction potential within the town where fully water saturated Holocene sediments are located, prompting reevaluation of the local earthquake hazard, seismic risk, and urban planning.
... P-wave velocity (Vp), thickness (H) and density (r) of different sub-surface mediums have been calculated. In general, the parameter of Vs is mostly use for soil classification and micro-zonation (Dobry et al. 2000;Wills 2000;Andrus and Stokoe 2000). For the 2-D profile plot, the data has been transferred to Surfer Software for interpolation by using the Kriging algorithm. ...
Integrated geophysical techniques have always been useful in identifying subsurface features. In the present study, three integrated geophysical methods of ground-penetrating radar (GPR), resistivity and Multi-channel Analysis (MASW) of surface waves have been utilized for near surface studies and identification of subsurface cavities near the Gadwalian dam. Acquisition of four inline and crossline profiles through GPR (100 MHz shielded antenna), two resistivity profiles through Imaging system and six seismic refraction profiles (MASW) have been made on the selected site having potential subsurface cavities. The processing and interpretation of GPR data through different software's exhibit variations in amplitude/diffraction patterns and several cavities have been identified in the GPR profiles. Sweetness attributes applied on the GPR data set also validate the cavities and unsaturated/saturated fractures. Slate beds and cavities have also been identified on pseudosections obtained through resistivity imaging. Further studies on 2D shear velocity (Vs30) profiles using MASW analysis for interpretation suggested that the absence of low velocity layer in shallow surface and velocity increase with respect to depth.
... However, in recent years, a topographic slope-based methodology has been adopted to quickly estimate ground motion in areas of the world for which detailed geophysical and borehole data are not accessible [21][22][23]. This topographic slope methodology uses proxy correlations between slope and Vs30 to create a site response map [22][23][24][25]. Topographic slope correlates quite well with Vs30 because stiffer rocks, which are associated with higher Vs30 values, tend to maintain steeper slopes. ...
The topographic slope method is an innovative, fast and very low-cost technique for estimating the average S-wave velocity in the upper 30 m (Vs30) based on the relationship between this quantity and the slope of the ground, obtained using a Digital Elevation Model (DEM). The method is based on the good linear correlations log(Vs30)-log(slope) found experimentally, which, ideally, should be determined for each region. If measured Vs30 data are not available to carry out this fitting for the study area, correlations from other areas could be used, although the reliability of the estimated Vs30 results would be lower. In this article, Vs30 observations are made for the city of Almeria, using Spatial Autocorrelation Surveys (SPAC) and Multichannel Analysis of Surface Waves (MASW), obtaining two types of fitting: (a) linear relationship log(Vs30)-log(slope); and (b) considering additional dependence on geological units. The reliability, evaluated by Multiple R-Squared (MRS), varies between 79.2% in the first case and 87.0% in the second, lowering the mean absolute values of the residuals at the observation points in the first case from 40.0 m/s to 29.0 m/s. Using a more generic correlation obtained for other areas of the world, the mean absolute residuals increase to 74.7 m/s.
... They determined the best predicted value of V S30 for each terrain category when the iteration achieved the lowest value of the mean squared prediction error. The stability and accuracy of the terrain-based prediction model were veri ed through comparison with the slope-based method (Wald and Allen 2007) and the geology-based method (Wills et al. 2000). Because most V S30 data considered in developing the Y12 model were not from measured data, only 503 V S30 measurements were used in developing the subsequent V S30 prediction model (the Y16 model) in Yong (2016). ...
Time-averaged shear-wave velocity to 30 m ( V S30 ) is commonly used in ground motion models as a parameter for evaluating site effects. This study used a collection of boreholes in Beijing, Tianjin, Guangxi, Guangdong, and three other municipalities and provinces, which were divided into three regions with reference to the seismic ground motion parameter zonation map of China, to establish V S30 prediction models based on terrain categories. Regional effects were verified by comparing morphometric parameters (topographic slope, surface texture, and local convexity) thresholds and terrain classification maps obtained from the global digital elevation model (DEM) data and the regional DEM data of the three regions. Additionally, V S30 prediction models for the three regions using both types of terrain classification maps were established and analyzed comparatively to provide credible regional V S30 models for China. Through analysis of the correlations between the measured V S30 values and the predicted V S30 values, and with consideration of the geological characteristics of the boreholes, the V S30 prediction models based on terrain classification maps from regional data were finally applied in developing regional V S30 models for China. Intercomparison of the V S30 prediction models for the three regions indicated that subregional consideration is necessary in terrain classification. Finally, a spatial analysis method adopting inverse distance weighting of the residuals was used to update the initial V S30 models. The developed V S30 models could be used both in developing regional ground motion models and in the construction of earthquake disaster scenarios.
... The Newcastle earthquake of 1989 demonstrated the spatial correlation between site conditions and building damage (Chandler et al., 1991). The site classification scheme was developed by Wills et al. (2000) validated for several Quaternary and unconsolidated deposits in several Australian sites such as Perth, Sydney, and Newcastle urban areas, using shear wave velocity of 30 m of soil (Vs30) data from previous geotechnical investigations. Vs30 information demonstrates the unit age and grain size influence on site classification (Tallett-Williams, 2017). ...
Australia is a relatively stable continental region but not tectonically inert, having geological conditions that are susceptible to liquefaction when subjected to earthquake ground motion. Liquefaction hazard assessment for Australia was conducted because no Australian liquefaction maps that are based on modern AI techniques are currently available. In this study, several conditioning factors including Shear wave velocity (Vs30), clay content, soil water content, soil bulk density, soil thickness, soil pH, distance from river, slope and elevation were considered to estimate the liquefaction potential index (LPI). By considering the Probabilistic Seismic Hazard Assessment (PSHA) technique, peak ground acceleration (PGA) was derived for 50 yrs period (500 and 2500 yrs return period) in Australia. Firstly, liquefaction hazard index (LHI) (effects based on the size and depth of the liquefiable areas) was estimated by considering the LPI along with the 2% and 10% exceedance probability of earthquake hazard. Secondly, ground acceleration data from the Geoscience Australia projecting 2% and 10% exceedance rate of PGA for 50 yrs were used in this study to produce earthquake induced soil liquefaction hazard maps. Thirdly, deep neural networks (DNNs) were also exerted to estimate liquefaction hazard that can be reported as liquefaction hazard base maps for Australia with an accuracy of 94% and 93%, respectively. As per the results, very-high liquefaction hazard can be observed in Western and Southern Australia including some parts of Victoria. This research is the first ever country-scale study to be considered for soil liquefaction hazard in Australia using geospatial information in association with PSHA and deep learning techniques. This study used an earthquake design magnitude threshold of Mw 6 using the source model characterization. The resulting maps present the earthquake-triggered liquefaction hazard and are intending to establish a conceptual structure to guide more detailed investigations as may be required in the future. The limitations of deep learning models are complex and require huge data, knowledge on topology, parameters, and training method whereas PSHA follows few assumptions. The advantages deal with the reusability of model codes and its transferability to other similar study areas. This research aims to support stakeholders’ on decision making for infrastructure investment, emergency planning and prioritisation of post-earthquake reconstruction projects.
... In many circumstances, it is widely accepted that site characterization based on shear wave velocity is one of the critical factors in determining the intensity of ground shaking (Joyner et al. 1994;Dobry et al. 2000;Borcherdt 2002). Thus, this is a practical parameter for characterizing local soil conditions for ground motion studies (Park and Elrick 1998;Wills et al. 2000Wills et al. , 2015Rahman et al. 2018;Biswas et al. 2018). In particular, seismic surface wave velocity is frequency dependent, and wave propagation relies on the dispersive nature of Rayleigh-type surface waves in layered media (Seligson 1970). ...
The high seismicity and tectonic activity of the study area located in a near-fault region in Gölyaka, Düzce, results in a bedrock geometry highly complex in the sense of faulting and deformation. This makes this area very challenging in terms of a site response study that would aid seismic hazard assessment. This study develops a basin model to evaluate the site effects in the tectonically formed Plio-Quaternary fluvial sedimentary layers of the Gölyaka region. The selected site uniquely falls within the near-field domain of a section of the North Anatolian Fault System. To determine the presence of these lateral variations in the geology as well as the geometry of the basin over a wide area, surface seismic measurements and deep vertical electrical sounding along with geotechnical boring studies have been performed, and a 3D basin geometry model was developed. The basin model shows that the sediment thickness continues to a depth of approximately 250–350 m with an irregular geometry due to over-step faulting near the southern boundary of the basin. Consequently, this study confirms the spatial variations in the near-field area that depend on basin geometry, material heterogeneity, and topography, indicating dipping and nonuniform stratification in the velocity profiles. Furthermore, the conducted microtremor measurements were used to compare the natural periods of microtremor results, along with interpolated Vs profiles to validate estimated basin depths. In conclusion, this study indicates that a well-developed basin geometry that reflects the complex process associated with the characteristics of the near-fault region could be accurately and reliably determined by developing a 3D basin model to assess site response in an account for seismic hazard assessment studies.
... Tinsley and Fumal (1985) classified the mean V S by geologic age in the Los Angeles earthquake hazard evaluation. Wills and his coworkers developed geologicbased correlations for California by grouping geologic units according to comparable V S30 values (Wills et al., 2000;Wills and Clahan, 2006;Wills et al., 2015). One important limitation of geological-based techniques is that, being ordinal data but not interval data, geologic units unavoidably have "boundaries," so the estimated V S30 is also given artificial boundaries. ...
We propose a new framework of VS30 proxy based on Cokriging method and apply the framework to build a VS30 map for mainland China. This framework utilizes the VS30–topographic slope correlation in the cross-semivariogram to benefit VS30 estimation and has the following benefits: (1) the estimation results are consistent with the measurement data; (2) the estimation uncertainty can be represented by error variance at each unsampled location according to the spatial structure of VS30 and topographic slope; (3) the result map does not have artificial boundaries; and (4) the estimation results can reflect the spatial relation between VS30 and topographic slope and the spatial relation of local spatial environment of topographic slope. We quantify the performance of this framework and compare it with that of three other topographic slope-based VS30 proxy models, including original models developed from exogenous data and models developed from China local data. The result shows that the framework proposed in this article has the best performance. The framework is applied to 7797 borehole VS30 measurements to build a VS30 map for mainland China. The map can capture the high VS30 values in regions where the geological conditions are dominated by flat-lying rocks. Moreover, we consider the effect of sample bias that comes from oversampling of borehole profiles in flat terrain regions when applying borehole data in the proposed framework. We utilize the relation of VS30 and topographic slope to quantify this bias, and use a distance-related data spatial declustering method to eliminate it.
... Intuitively, near-surface structure with coarse-grained sediments, such as sands and gravels, should have faster velocities than fine-grained sediments, such as silt and clay, due to their different material properties and depositional environments where coarse-grained sediments are often deposited on steeper slopes. Such interpretations are used in defining site classes based on measured profiles (Wills et al., 2000); however, this correlation often does not hold when inferring Vs30 using large-scale geological maps. Studies commonly demonstrate that locations defined as "coarse-grained sediments" do not have significantly different Vs30 from locations defined as "fine-grained sediments" (e.g., S. Park & Elrick, 1998). ...
One of the main sources of seismic noise below 0.05 Hz is the atmospheric pressure variation, especially when surface pressure variations are large. When surface broadband seismic stations are equipped with pressure sensors, there is high coherence between pressure and seismic signals at low frequencies. The amount of ground deformation under surface pressure variations reflects the characteristics of near‐surface elastic structure and allows us to estimate near‐surface shear‐modulus structure using an inversion method. In the inversion method, we have the surface observable η(f) = Sz/Sp, where f is a frequency between 0.01 and 0.05 Hz, and Sz and Sp are the power spectral densities of vertical seismic data and of surface pressure data. We derive depth sensitivity kernels for η(f) with which we invert for elastic moduli of the shallow structure. Between 0.01 and 0.05 Hz, sensitivity kernels typically have peaks at depths within the uppermost 100 m. Based on vertically heterogeneous 1‐D structures, we estimate Vs30 at 744 USArray Transportable Array stations. Vs30 is the time‐averaged shear‐wave velocity from the surface to the 30‐m depth. We compare our results with various surficial geology maps. Although Vs30 has high horizontal variability over a short distance on the scale of hundreds of meters, we find correlations between Vs30 and large‐scale geological structures, such as mapped units and surficial materials. We find good agreement between estimated Vs30 and mapped Quaternary sediment depths, where stations with thicker underlying sediment tend to have slower Vs30.
... However, V S30 measurements are not always available in practice and instead several proxy methods have been proposed over the years. In the United States, a first effort was made by Wills et al. (2000) who prepared a site-category map of California by classifying geologic units based on V S30 s measured in 556 profiles. This study was followed by Wills and Clahan (2006) who used 19 geologically defined categories to develop maps of Vs characteristics in California and the recent update by Wills et al. (2015) who characterized with greater accuracy the V S of the young alluvial deposits. ...
The Alaska Regional Network and Transportable Array provide an invaluable waveform data set for studying ground motions in Alaska. However, the data set is useful only after the site effects at each station are well understood. Considering the large number of stations associated with these networks, it would be onerous to measure the sub-surface velocity structure beneath every station using geophysical exploration techniques involving arrays, such as active-source or passive-source non-invasive array methods. Instead, it is more economical to estimate the site conditions using waveforms recorded at the seismic stations. Most of the methods for estimating site response from recorded waveforms use the frequency-dependent ratio between the horizontal and vertical component of either ambient noise or S waves from earthquakes. We instead use the horizontal and vertical component of P waves to infer the sub-surface velocity structure. It has been demonstrated that the ratio of radial to vertical P waves is mostly sensitive to sub-surface shear velocity. Therefore, the sub-surface velocity structure can be estimated using an approach similar to teleseismic P receiver functions, but at much smaller scale and higher frequency. The results from this method are in good agreement with results from active-source or passive-source non-invasive array methods and have been widely used in the Central Eastern United States. The Alaska Regional Network and Transportable Array have recorded numerous earthquakes in the magnitude range of interest and at shallow depth, which provides an ideal opportunity for this study. V S 30 is used to represent the site amplification of ground motions in all ground motion models that are used in generating the US Geological Survey’s National Seismic Hazard Maps, as well as in the professional practice of seismic hazard analysis. The results of this work provide a basis for improved site-specific hazard estimates in Alaska.
... CVM-S4 also includes a geotechnical layer (GTL) to describe the material in the uppermost 300 m of the model (Magistrale et al., 2000). The GTL for CVM-S4 is constrained by V p and V s borehole measurements and is implemented for a particular location using a weighted average of nearby profiles and a mean profile corresponding to the NEHRP category (as implemented by Wills et al., 2000) at that site. CVM-S4.26 is the 26th and most recent full-3D tomographic inversion iteration of the velocity structure. ...
We introduce procedures to validate site response in sedimentary basins as predicted using ground motion simulations. These procedures aim to isolate contributions of site response to computed intensity measures relative to those from seismic source and path effects. In one of the validation procedures, simulated motions are analyzed in the same manner as earthquake recordings to derive non-ergodic site terms. This procedure compares the scaling with sediment isosurface depth of simulated versus empirical site terms (the latter having been derived in a separate study). A second validation procedure utilizes two sets of simulations, one that considers three-dimensional (3D) basin structure and a second that utilizes a one-dimensional (1D) representation of the crustal structure. Identical sources are used in both procedures, and after correcting for variable path effects, differences in ground motions are used to estimate site amplification in 3D basins. Such site responses are compared to those derived empirically to validate both the absolute levels and the depth scaling of site response from 3D simulations. We apply both procedures to southern California in a manner that is consistent between the simulated and empirical data (i.e. by using similar event locations and magnitudes). The results show that the 3D simulations overpredict the depth-scaling and absolute levels of site amplification in basins. However, overall patterns of site amplification with depth are similar, suggesting that future calibration may be able to remove observed biases.
... The relationship between the AF derived from the Groningen borehole locations and local site conditions is investigated in the following. Many ground motion prediction equations which include site response consider the shear-wave velocity for the top 30 m (V s30 ) as the main parameter affecting amplification (Akkar et al., 2014;Bindi et al., 2014;Kruiver et al., 2017b;Wills et al., 2000), as well as Eurocode 8 (Comité Européen de Normalisation, 2004). However, studies (Castellaro et al., 2008;Kokusho and Sato, 2008;Lee and Trifunac, 2010) have drawn attention to the fact that using only V s30 as a proxy for site response is inadequate, because it does not uniquely correlate with amplification. ...
Earthquake site response is an essential part of seismic hazard assessment, especially in densely populated areas. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on the amplitude of ground shaking. Even though the Netherlands is a low- to moderate-seismicity area, the seismic risk cannot be neglected, in particular, because shallow induced earthquakes occur. The aim of this study is to establish a nationwide site-response zonation by combining 3D lithostratigraphic models and earthquake and ambient vibration recordings.
As a first step, we constrain the parameters (velocity contrast and shear-wave velocity) that are indicative of ground motion amplification in the Groningen area. For this, we compare ambient vibration and earthquake recordings using the horizontal-to-vertical spectral ratio (HVSR) method, borehole empirical transfer functions (ETFs), and amplification factors (AFs). This enables us to define an empirical relationship between the amplification measured from earthquakes by using the ETF and AF and the amplification estimated from ambient vibrations by using the HVSR. With this, we show that the HVSR can be used as a first proxy for site response. Subsequently, HVSR curves throughout the Netherlands are estimated. The HVSR amplitude characteristics largely coincide with the in situ lithostratigraphic sequences and the presence of a strong velocity contrast in the near surface. Next, sediment profiles representing the Dutch shallow subsurface are categorised into five classes, where each class represents a level of expected amplification. The mean amplification for each class, and its variability, is quantified using 66 sites with measured earthquake amplification (ETF and AF) and 115 sites with HVSR curves.
The site-response (amplification) zonation map for the Netherlands is designed by transforming geological 3D grid cell models into the five classes, and an AF is assigned to most of the classes. This site-response assessment, presented on a nationwide scale, is important for a first identification of regions with increased seismic hazard potential, for example at locations with mining or geothermal energy activities.
... from a vertically incident shear wave by placing an earthquake source beneath each station of the survey and propagating them to the surface (e.g., Bowden & Tsai, 2017;Jia & Clayton, 2021;Wills et al., 2000). For a source, we use a horizontal force injected by a 2 Hz Ricker wavelet located at 2-km depth ( Figure 15). ...
The metropolitan Los Angeles region represents a zone of high-seismic risk due to its proximity to several fault systems, including the San Andreas fault. Adding to this problem is the fact that Los Angeles and its surrounding cities are built on top of soft sediments that tend to trap and amplify seismic waves generated by earthquakes. In this study, we use three dense petroleum industry surveys deployed in a 16x16-km area at Long Beach, California, to produce a high-resolution model of the top kilometer of the crust and investigate the influence of its structural variations on the amplification of seismic waves. Our velocity estimates reveal substantial lateral contrasts and correlate remarkably well with the geological background of the area, illuminating features such as the Newport-Inglewood fault, the Silverado aquifer, and the San Gabriel river. We then use computational modeling to show that the presence of these small-scale structures have a clear impact on the intensity of the expected shaking, and can cause ground-motion motion acceleration to change by several factors over a sub-kilometer horizontal scale. These results shed light onto the scale of variations that can be expected in this type of tectonic settings and highlight the importance of resolution in modern-day seismic hazard estimates.
... The older the geological era (from Cenozoic to Paleozoic) is, V S30 is increased from cluster 3 to cluster 1. The trends of V S30 are also generally resemble with the correlated site classification with geological era (age) (Wills et al., 2000). When applying K-means, FF, Cobweb, DBSCAN, and consensus clustering, the division of clusters by geological era was more obvious. ...
The site classification system in the seismic design code and its dependent zonation should be guaranteed to represent the local spatial uncertainty of subsurface features, but have been uniformly used based on the site response parameters. Spatial interpolation-based zonation is only practically feasible if there are clear-cut stochastic/spatial correlations in geotechnical/geophysical measurements. The geology and terrain features can be substituted as an influential proxy for site amplification. To develop cluster-oriented zonation considering the spatial heterogeneity of the different site response parameters focusing on an uninvestigated area, this study proposes a new approach for multivariate site classification blended with geographic information system (GIS)-based spatial clustering and machine learning (ML)-based clustering ensemble technologies. GIS-based clustering characterizes a hot spot cluster with statistical and spatial correlation values of the site response parameters and defines the relative weight using the Gi∗ Z-score as the index of spatial heterogeneity. ML-based clustering ensembles aim to combine the clustering model in terms of consistency and performance, and are designed for optimization through a consensus function by comparing the fitness with the site classification system to obtain better results than individual clustering algorithms. The novelty of the proposed workflow is the stepwise improvement of the proposed models compared with the zonation phases and practical methods.
... Many ground-motion prediction equations including site-response consider the shear-wave velocity for the top 30 m (V s 30 ) as the main parameter affecting amplification (Akkar et al., 2014;Bindi et al., 2014;Kruiver et al., 2017b;Wills et al., 2000), as well as Eurocode 8 (CEN et al., 2004). However, recent studies (Castellaro et al., 2008;Kokusho and Sato, 2008;Lee 250 and Trifunac, 2010) have drawn attention to the fact that using only V s 30 as proxy for site-response is inadequate, because it does not uniquely correlate with amplification, which is defined by several parameters like the depth and degree of the seismic impedance contrast. ...
Earthquake site-response is an essential part of seismic hazard assessment, especially in densely populated areas. The shallow geology of the Netherlands consists of a very heterogeneous soft sediment cover, which has a strong effect on seismic wave propagation and in particular on the amplitude of ground shaking, resulting in significant damage on structures despite the fact that the events are of small magnitude. Even though it is a low-to-moderate seismicity area, the seismic risk cannot be neglected, in particular, because shallow induced earthquakes occur. The aim of this study is to establish a nationwide site-response zonation by using the lithostratigraphy, earthquake- and ambient vibration recordings. In the first step, we constrain the parameters (velocity contrast and shear-wave velocity) that are indicative of ground-motion amplification in the Groningen area. For this, we combine ambient vibration and earthquake recordings using resp. the horizontal-to-vertical spectral ratio method (HVSR), borehole empirical transfer functions (ETFs) and amplification factors (AFs). This enables us to define an empirical relationship between measured earthquake amplification from the ETF and AF, and amplification estimated with the HVSR derived from the ambient seismic field. Therewith, we show that the HVSR can be used as a first proxy for amplification. Subsequently, HVSR curves throughout the Netherlands are estimated. The resulting peak amplitudes largely coincide with the in-situ lithostratigraphic sequences and the presence of a strong velocity contrast in the near-surface. Next, sediment profiles representing the Dutch shallow subsurface are categorized into five classes, where each class is representing a level of expected amplification. The mean amplification for each class, and its variability, is quantified using 66 sites with measured earthquake amplification (ETF and AF) and 115 sites with HVSR curves. The site-response (amplification) zonation map for the Netherlands is designed by transforming published geological 3D grid cell models into the five classes and an AF is assigned to most of the classes. This presented site-response assessment on a national scale is important for a first identification of regions with increased seismic hazard potential, for example at locations with mining or geothermal energy activities.
... A transect in Los Angeles, California, crossed both the San Gabriel and Los Angeles basins with 200 profiles over 60 km ( Fig. 1; Thelen et al. 2006). Transect velocity measurements followed the predictions of Wills et al. (2000) as well as available Rosrine suspensionlogger results from nearby deep boreholes. A transect through Las Vegas, Nevada, measured 47 profiles over a distance of 13 km . ...
The geotechnical industry has widely adopted the refraction microtremor shear-wave velocity measurement technique, which is accepted by building authorities for evaluation of seismic site class around the world. Clark County and the City of Henderson, Nevada, populated their Earthquake Parcel Map with over 10,000 site measurements for building code enforcement, made over a 3-year period. 2D refraction microtremor analysis now allows engineers to image lateral shear-wave velocity variations and do passive subsurface imaging. Along with experience at a basic level, the ability to identify the “no energy area” and the “minimum-velocity envelope” on the slowness-frequency ( p-f ) image helps practitioners to assess the quality of their ReMi data and analysis. Guides for grading ( p-f ) image quality, and for estimating depth sensitivity, velocity-depth tradeoffs, and depth and velocity resolution also assist practitioners in deciding whether their refraction microtremor data will meet their investigation objectives. Commercial refraction microtremor surveys use linear arrays, and a new criterion of 2.2% minimum microtremor energy in the array direction allows users to assess the likelihood of correct results. Unfortunately, any useful and popular measurement technique can be abused. Practitioners must follow correct data collection, analysis, interpretation, and measurement procedures, or the results cannot be labeled “refraction microtremor” or “ReMi” results. We present some of the common mistakes and provide solutions with the objective of establishing a “best practices” template for getting consistent, reliable models from refraction microtremor measurements.
... GMPEs that have been considered for use in this study for developing the CMS for SEA is consistent with a time-averaged bedrock shear wave velocity of around 760ms À 1 which is representative of SEA conditions and fits with B/C site class as per the National Earthquake Hazard Reduction Program classification scheme (Wills et al. 2000). In summary, the five shortlisted GMPEs employed in this study for developing CMS for SEA are namely CAM, A12, SGC09, ASK14 and CY14. ...
This paper presents an application of the Conditional Mean Spectrum (CMS) methodology for sourcing accelerogram records for use in dynamic analyses of structures in intraplate regions of lower seismicity. The main challenges with deriving CMS for selecting and scaling accelerograms in regions of lower seismicity stem from the paucity of representative strong motion data and event recurrence data. A step-by-step illustration of the methodology is presented using the south-eastern Australia (SEA) region as an example. The study involves making use of a diversity of Ground Motion Prediction Expressions (GMPEs) including a recently developed regionally adjustable Component Attenuation Model (CAM). Three different schemes using a weighted averaging of candidate GMPEs were adopted and a comparison of predictions demonstrated only minor differences confirming the robustness of the modelling. The CMS constructed in this study have been used to develop a proposed suite of scaled accelerograms for SEA.
... The soil samples are classified into six different categories from A to F according to NEHRP norms given in Table 1 (Wills, et al., 2000). The predominant periods for the ground surface and average shear wave velocity up to 30 m were taken into account for the classification of the soils. ...
Derince town is one of the most densely industrialized (oil refineries, ports, etc.) and populated urban areas which is located in one of the highest seismically active regions in Turkey. The area was damaged by a severe earthquake on 17 August 1999 in Kocaeli (Mw = 7.4). The geotechnical properties of layers play the most important role in the formation of damage. One of the weakness indicators for the soil structure in a region is the ground vulnerability indices (Kg). The reduction of damage from earthquakes is related to the knowledge of these ground properties. Therefore, the microtremor horizontal-to-vertical spectral ratio (HVSR) method was applied to single site measurements at 43 stations over an area of 40 km ² to evaluate local site effects in terms of ground vulnerability indices (Kg), fundamental frequency and amplification factor. Structural damage occurring during the August 17, 1999 Kocaeli (M w =7.4) earthquake is compared with the estimated ground vulnerability indices. The results indicate that the K g values are in good agreement with damage distribution. Large K g values indicate weak points in the study area. According to results, the areas with Kg values greater than 14 seem to be the most vulnerable locations in the study. The Kg and soil types overwhelmingly comply with each other very well. Poor ground conditions are seen in areas with high vulnerability. Ground conditions should be taken into account during the planning and design of urban areas. The results obtained by considering ground conditions can be used as a quick method to identify risky areas.
... Only V S profiles that were measured in situ (i.e. 557) were included in the final data collection and were also partially used in a study by Wills et al. (2000). These V S profiles were also classified according to GeoMatrix (Chiou et al. 2008) and to the thirty-meter harmonic shear wave velocity (V S,30 ) proxies. ...
The compilation and maintenance of experimental databases are of crucial importance in all research fields, allowing for researchers to develop and test new methodologies. In this work, we present a flat-file database of experimental dispersion curves and shear wave velocity profiles, mainly from active surface wave testing, but including also data from passive surface wave testing and invasive methods. The Polito Surface Wave flat-file Database (PSWD) is a gathering of experimental measurements collected within the past 25 years at different Italian sites. Discussion on the database content is reported in this paper to evaluate some statistical properties of surface wave test results. Comparisons with other methods for shear wave velocity measurements are also considered. The main novelty of this work is the homogeneity of the PSWD in terms of processing and interpretation methods. A common processing strategy and a new inversion approach were applied to all the data in the PSWD to guarantee consistency. The PSWD can be useful for further correlation studies and is made available as a reference benchmark for the validation and verification of novel interpretation procedures by other researchers.
... 1-D shear wave velocity (Vs) profiles are widely used in seismic site classification based on Vs30 values (average Vs for the top 30 m, e.g. Wills et al. 2000;Kanlı et al. 2006;Lee & Tsai 2008, Zor et al. 2010, geotechnical characterization (Stokoe et al. 1994;Foti 2000Foti , 2005Rix et al. 2000), site response analysis (e.g. Malagnini et al. 1993;Bozdag & Kocaoglu 2005;Parolai et al. 2006) and seismic hazard assessment studies (e.g. ...
We present a new processing scheme that employs passive seismic interferometry followed by multichannel analysis of surface waves, which we call the 2D PSI-MASW method, to obtain Rayleigh wave phase velocity dispersion (PVD) information. In this scheme, we first use the principles of passive seismic interferometry to form multi-directional cross-correlations (CCs) then project the CCs onto a 1-D virtual array and apply the phase-shift transform as in MASW processing. We compare PVD information obtained by this method with those of the conventional beam-power based frequency–wavenumber decomposition (CVFK) method using ambient seismic noise (ASN) data collected by local-scale 2-dimensional (2D) arrays deployed at three selected sites in Bursa, Turkey. By analysing the ASN data from these sites, we show that similar multi-modal PVD curves can be obtained with the two methods over a broad frequency range (∼2-23 Hz) within the wavenumber resolution and aliasing limits. However, in one of our sites where the 2D array configuration has a considerable anti-symmetry, we show that the 1D virtual array used in the 2D PSI-MASW method has a better array response function in terms of wavenumber resolution and suppression of side-lobes leading to superior mode resolution and separation than that of the CVFK method, which shows strong directional variations. Furthermore, unlike the CVFK method, the 2D PSI-MASW method takes advantage of temporal stacking of CCs ensuring weak but coherent Rayleigh wave signals present in the ASN wavefield to be strengthened and has the potential for better extraction of PVD information. We conclude that by using a 2D array with spatial coverage providing a wide range of directions and distances, reliable PVD information can be obtained even if the ASN sources are not concentrated in the stationary phase zones. Thus, we suggest that the 2D PSI-MASW method is highly advantageous for the extraction of reliable PVD information owing to the multi-directional CCs provided by the 2D array configurations. We also report that using only a single receiver line in the interferometric approach results in biased and/or incomplete PVD information due to the non-isotropic ASN source distribution at all three sites we analysed. In conclusion, our results clearly indicate that the 2D PSI-MASW method can be used as complementary or alternative to the CVFK method to extract multi-modal Rayleigh wave PVD information in local-scale seismological studies.
... Therefore, V S30 estimates for the sites have been adopted from two sources: the Australian Seismic Site Conditions Map (ASSCM; McPherson, 2017) and the Wald and Allen (2007) V S30 estimates based on topographic gradient. The ASSCM provides an estimation of site conditions that corresponds to the modified National Earthquake Hazards Reduction Program site classification (Wills et al., 2000), using surficial geology as well as weathering indexes (Wilford, 2012). These site classes are mapped to a representative V S30 -value (McPherson, 2017). ...
The 19 June 2012 local magnitude ML 5.4 (Mw 5.1) Moe earthquake, which occurred
within the Australian stable continental region, was the largest seismic event for
the state of Victoria, for more than 30 yr. Seismic networks in the southeast
Australian region yielded many high-quality recordings of the moderate-magnitude
earthquake mainshock and its largest aftershock (ML 4.4 and Mw 4.3) at a range of distances from the epicenter. The source and attenuation characteristics of the earthquake
sequence are analyzed. Almost 15,000 felt reports were received following the mainshock, and its ground motions tripped a number of coal-fired power generators in the
region amounting to the loss of, approximately, 1955 MW of generation capacity. The
attenuation of macroseismic intensities is shown to mimic the attenuation shape of
eastern North America (ENA) models but requires an interevent bias to reduce predicted
intensities. Furthermore, instrumental ground-motion recordings are compared to
ground-motion models (GMMs) considered applicable for the southeastern
Australian (SEA) region. Some GMMs developed for ENA and SEA provide reasonable
estimates of the recorded ground motions of spectral acceleration within epicentral distances of, approximately, 100 km. The mean Next Generation Attenuation-East GMM,
recently developed for stable ENA, performs relatively poorly for the 2012 Moe earthquake sequence, particularly, for short-period accelerations. These observations will
help inform future seismic hazard assessments for eastern Australia.
... Another significant parameter in estimating dynamic responses of the soils is the mean shear wave velocity for the soil in the upper 30 m of the ground surface (V S30 ), which is obtained by dividing 30 m with the required time for the waves to pass the surficial 30 m (Dobry et al. 2000;BSSC 2001;Boore 2004). Site classifications using the V S30 values are needed for specifying site response in regression formulas (Boore et al. 1997(Boore et al. , 2011Thompson and Wald 2016) and for generating site classification maps based on the National Earthquake Hazard Reduction Program (NEHRP) soil classification system (Wills et al. 2000;Rodriguez-Marek et al. 2001). ...
This paper presents a study on the seismic site classification map using the geophysical tests in Kahramanmaras city located at a place where African, Anatolian, and Arabian plates meeting in southern-central Turkey. Generating seismic site classification maps in accordance with National Earthquake Hazards Reduction Program (NEHRP) has become a more significant criterion for earthquake hazard estimations. The SPT-N values obtained from the field studies at 287 boreholes within the upper 30 m were used to describe the subsurface conditions in the region. The shear wave velocity (VS) values in the study area were obtained by implementing Multichannel Analysis of Surface Waves (MASW) and Microtremor Array Method (MAM) measurements tests. An approach proposed by Boore (Boore, Bull Seismol Soc Am 94:591–597, 2004) for the cases where the VS measurements do not reach 30 m depth has also been adopted by correlating the shallow shear wave velocity with VS30. The resulting site classification maps estimate that the study area is predominantly classified as soil site class C, while the small areas were rarely classified as soil site class D and B. Furthermore, a systematic analysis based on a comparative study of the present research and the published correlations for seismic site classification with VS30 values has been carried out using Geographical Information System (GIS). Evidently, the VS30 based seismic site classification maps could be effectively used by researchers and engineers for the purpose of land-use planning and urban development in earthquake-prone regions.
... However, the V s30 is related to the type of rock mass and soil mass, which is difficult to obtain with a large number of field measurements on the regional scale. According to the relevant codes (Eurocode 82,003; The Ministry of Construction of the People's Republic of China 2010), previous research results (Wills et al. 2000, Wills 2006Rapolla et al. 2010Rapolla et al. , 2012Paoletti et al. 2013;Caccavale et al. 2017) and public and private technical reports, we obtained the V s30 of four lithological groups, as shown in Table 3. Previous studies have developed an empirical equation to obtain the amplification effect using V s30 and PGA information (Choi and Stewart 2005;Bhatt et al. 2019). ...
Critical acceleration is an inherent property of a slope and determines the slope stability under seismic action. The critical acceleration model is a core element of regional seismic landslide hazard assessment. Therefore, the purpose of this paper is to reveal the influence of different critical acceleration models on assessments of potential earthquake–induced landslide hazards. Traditionally, the Newmark critical acceleration model has commonly been used to evaluate the potential earthquake–induced landslide hazard. This method needs to assume the failure depth of the slope, which leads to an underestimation of the predicted displacement of the seismic landslide. Recently, the prediction equations of critical acceleration based on a parametric study of the limit equilibrium method overcomes the limitation of Newmark critical acceleration model and has been applied to assessments of co-seismic landslide hazards. In this study, we use Newmark critical acceleration model and prediction equations of critical acceleration to obtain the distribution maps of potential earthquake–induced landslide hazard in Shimian County, with peak ground acceleration of 10% and 2% exceeding the probability in 50 years. In addition, the nonlinear effect of site and topographic effects on peak ground acceleration were considered. The results show that Newmark critical acceleration model underestimates the area and value of the predicted displacement, while prediction equations of critical acceleration produces seismic landslides in a wider range of mountainous areas. This indicates that the critical acceleration model has a significant influence on assessments of potential earthquake–induced landslide hazards. In addition, the study not only provides valuable reference for assessment of potential earthquake–induced landslide hazard, emergency response of seismic landslides, and land planning in the study area, it also provides a useful demonstration for the selection of a critical acceleration model in seismic landslide hazard assessments for future researches.
... Comparison of predictions of different models for duration with results from this study. In all plots, V S30 is 760 m/s and NEHRP Site class B (Wills et al., 2000) is used for models that included site classification, and rock sites are used for models that had different predictions for soil and rock. ...
Significant duration of strong shaking quantifies the length of time during which strong earthquake-induced shaking occurs at a given site. Significant duration has multiple applications in Geotechnical and Structural Engineering. However, while multiple ground motion prediction (GMPE) equations for duration exist for shallow crustal tectonic environments, at the time of this publication, there are few published models for predicting significant duration of subduction earthquakes. To address this need and to identify the difference between significant duration of motions resulting from earthquakes in different tectonic regimes, we develop predictive equations for significant duration applicable to interface and intraslab subduction earthquakes and shallow crustal earthquakes in active tectonic regimes using the KiK-net ground motion database. The GMPEs are applicable to earthquakes with M4 to 9. In addition, the influence of earthquake magnitude on duration due to path effects is captured in the proposed relationships. Based on the relationships proposed in this study, we note that the duration of ground motions from subduction earthquakes is longer than those of shallow crustal earthquakes that have similar magnitudes and distances. The predictions of duration for shallow crustal earthquakes in active tectonic regimes developed in this study are consistent with those from previous studies.
... e National Earthquake Hazard Reduction Program (NEHRP), which is one of the widely used systems for the SSC applications, classified the soils by using their V S values in designing building codes and characterizing site response [5,6]. e objective of this study is to make an SSC assessment in the city of Kahramanmaras located in a seismically active region in southern-central Turkey. ...
Assessment of seismic site classification (SSC) using either the average shear wave velocity (VS30) or the average SPT-N values (N30) for upper 30 m in soils is the simplest method to carry out various studies including site response and soil-structure interactions. Either the VS30- or the N30-based SSC maps designed according to the National Earthquake Hazards Reduction Program (NEHRP) classification system are effectively used to predict possible locations for future seismic events. The main goal of this study is to generate maps using the Geographic Information System (GIS) for the SSC in Kahramanmaras city, influenced by both East Anatolian Fault and Dead Sea Fault Zones, using both VS30 and N30 values. The study also presents a series of GIS maps produced using the shear wave velocity (VS) and SPT-N values at the depths of 5 m, 10 m, 15 m, 20 m, and 25 m. Furthermore, the study estimates the bed rock level and generates the SSC maps for the average VS values through overburden soils by using the NEHRP system. The VS30 maps categorize the study area mainly under class C and limited number of areas under classes B and D, whereas the N30 maps classify the study area mainly under class D. Both maps indicate that the soil classes in the study area are different to a high extent. Eventually, the GIS maps complied for the purpose of urban development may be utilized effectively by engineers in the field.
... Maumere is located within the Ende region, in the area of volcanic rock (lava, pumice breccia, tuff) of Quarter -Tersier (Qtv) [10]. To calculate the peak ground acceleration, I used Vs 360 km/s for the Quarter volcanic rock [11], [12]. ...
... SM it is widely accepted as an effective seismic risk mitigation tool that can increase the degree of resilience of the territory and populations, providing useful information for urban planning, land management, emergency planning and post-seismic reconstruction (e.g. Ansal et al. 2010;Markušić and Herak 1998;Poggi and Fäh 2016;Wills et al. 2000; see also Pagliaroli 2018 and references therein). National guidelines and standards were provided for these studies by Italian Department of Civil Protection (DPC) to ensure the homogeneity of the products (ICMS 2008, SM Working Group 2015, while the reliability of the results is guaranteed by Regional and National committees composed by scientific experts (i.e. ...
Site effects in consequence of the 2016–2018 Central Italy seismic sequence “marked the fate” of many villages located close to the epicenters along the Apennine chain. Pescara del Tronto, a small settlement located on a mountain slope in the municipality of Arquata del Tronto, (AP) is very representative of such territories since, early after the onset of the seismic sequence, suffered very impressive site effects, including a large seismically-induced debris flow and a high number of small volume landslides. This paper describes the main results of the scientific activities carried out by the authors in this locality in the framework of the unprecedented large-scale Seismic Microzonation project funded by Italian Government in Central Italy for 138 territories. Through an intense field activity, the geological and geomorphologic setting of the study area were revised and updated, including a landslide susceptibility assessment that helped the Italian Department of Civil Protection in the emergency management for temporary housing and, later on, was included in the 3rd Level Seismic Microzonation study implemented by authors while the seismic sequence was still ongoing. A very detailed and reliable subsoil model for this municipality was defined, despite difficulties faced in performing direct and indirect investigations due to the safety restrictions for many areas. The Local Seismic Site response was finally assessed for this locality and the results discussed. A key role in the occurrence of strong site effects into Pescara del Tronto has been played by quaternary deposits having an unexpected heterogeneity under the old village.
... Because ground motions can be significantly amplified (or de-amplified) by seismic site conditions, we develop a site condition map for mainland China using geology as a proxy to define the National Earthquake Hazards Reduction Program (NEHRP) site categories (Wills and Clahan, 2006;Wills et al., 2000Wills et al., , 2015. We obtain the geology information from two sources: a bedrock geology database with a scale of 1:1,000,000 (Ding et al., 2011), and a Quaternary map with a scale of 1:2,500,000 (Zhang et al., 1990). ...
We construct a probabilistic seismic hazard model for mainland China by integrating historical earthquakes, active faults, and geodetic strain rates. We delineate large seismic source zones based on geologic and seismotectonic characteristics. For each source zone, a tapered Gutenberg–Richter (TGR) distribution is used to model the total seismic activity rates. The TGR a- and b-values are calculated using a new earthquake catalog, while corner magnitudes are constrained using the seismic moment rate inferred from a geodetic strain rate model. For hazard calculations, the total TGR distribution is split into two parts, with smaller ( M W < 6.5) earthquakes being distributed within the zone using a smoothed seismicity method, and larger earthquakes put both onto active faults, based on fault slip rates and dimensions, and into the zone as background seismicity. We select ground motion models by performing residual analysis using ground motion recordings. Site amplifications are considered based on a site condition map developed using geology as a proxy. The resulting seismic hazard is consistent with the fifth-generation national seismic hazard model for most major cities.
In this study, we explore whether the Parker and Baltay (2022) site response models for the Los Angeles (LA) basin region can improve ground-motion forecasts in the U.S. Geological Survey ShakeAlert earthquake early warning system (hereafter ShakeAlert). We implement the peak ground acceleration and peak ground velocity site response models of Parker and Baltay (2022) in ShakeAlert via the earthquake information to ground-motion (hereafter eqinfo2GM) module, which predicts ground motions from the estimated earthquake parameters of magnitude, rupture length, and location. The nonergodic site response models for the greater LA area were developed using ground motions from 414 M 3–7.3 earthquakes in southern California. We test nonergodic ground-motion forecasts for five earthquakes in the LA area: the 1994 M 6.7 Northridge earthquake, the 2008 M 5.4 Chino Hills earthquake, the 2019 M 7.1 Ridgecrest earthquake, the 2020 M 4.5 South El Monte earthquake, and a synthetic M 7.8 earthquake on the southern San Andreas fault from the ShakeOut scenario, which was the basis of a statewide emergency response exercise. From the test results, we find that with the nonergodic site response applied, ShakeAlert not only alerts larger areas but can also result in longer warning times in LA region. In addition, the modified Mercalli intensity (MMI) ground-motion predictions generated by the ShakeAlert eqinfo2GM module are improved in accuracy when compared with the corresponding ShakeMap ground-truth MMI when the nonergodic site response model is applied.
Shear-wave velocity (Vs) of soils in Nakhon Nayok City, Central Thailand were determined using the Multi-Channel Analysis of Surface Wave technique. The Vs. of 35 tested sites were weighted average to 30 m depth based on the National Earthquake Hazards Reduction Program (NEHRP) criteria, which revealed NEHRP site classes C, D, and E within the study area. Soil class C was found in the north of the city. Moreover, most of the residential area of Nakhon Nayok City is positioned on soil classes D and E. The soil in the area of study has an amplification value ranging from 1.4 to 3.9. The central and southwestern parts of the city, which mainly consist of soft sediments, have a higher amplification value than that in the northern part, which mainly consists of coarse grain soils of colluvial deposits. Based on the NEHRP and amplification value, the Nakhon Nayok City area will experience some effect from ground shaking from nearby and far away earthquake seismic sources.
The time-averaged shear wave velocity of top 30 m (V S30) is the most commonly used parameter to classify a site and evaluate its amplification characteristics for the seismic design. The in-situ seismic tests must be performed up to a depth of 30 m for obtaining the shear wave velocity (V S) profiles to estimate V S30. It is intimated that, in most of the cases, the measured V S profile does not extend up to 30 m due to numerous reasons including limitation of testing techniques and unfavorable field conditions. Since, the measurements of V S30 are unavailable for the majority of Pakistan and the world, the local geology and topographic slope or its combination are used to estimate V S30. However, there is no field-based validation of the estimated V S30 is performed in Islamabad-Rawalpindi region, the proxy-based estimation may lead to unrealistic results. To accommodate this, region specific extrapolation methods are developed. This study develops an empirical data-driven function of V S30 from shallow V S profiles by correlating V S30 with the time-averaged V S to depths less than 30 m. In this regard, 85 V S profiles are used from Rawalpindi-Islamabad region. A comparative analysis of the proposed procedure is carried out with the published methods. It is revealed that V S30 predicted by the proposed function results in close matches with the data measured in the western United States. In addition, the results indicate that the local geology and topographic slope proxies may not be acceptable for usage in the region due to their greater uncertainty. Finally, a procedure for extrapolating the V S profile from available shallow depth measurements up to 30 m is proposed.
Classification of local soil conditions is important for the interpretation of structural seismic damage, which also plays a vital role in site‐specific seismic hazard analyses. In this study, we propose to classify sites as an image recognition task using a deep convolutional neural network (DCNN)‐based technique. We design the input image as a combination of the topographic slope and the mean horizontal‐to‐vertical spectral ratio (HVSR) of earthquake recordings. A DCNN model with five convolutional layers is trained using 1649 sites in Japan. The recall rates for site classes C, D, and E using our DCNN classifier for Japanese sites are 82%, 70%, and 60%, respectively. When compared with existing site classification schemes relying on predefined standard HVSR curves, our proposed method achieves the highest total accuracy rate (between 73% and 75%). The generality and applicability of our trained classifier are further validated using sites in Europe with a total accuracy between 64% and 66%. The proposed data‐driven approach could be extended to other types of site amplification functions in the future.
Considering 869 ground-motion recordings from moderate-to-strong earthquakes that occurred in 2007–2019, this work investigates the variation of site amplification factors and develops an empirical site amplification model of the north–south seismic belt of China. The work first regresses a simple empirical ground-motion model (GMM) for the averaged reference site (the average shear-wave velocity for the top 30 m of the Earth (VS30) is about 760 m/s) by 322 recordings of the dataset. The regressed reference site model indicates that the slow distance attenuation still exists in earthquakes of the north–south seismic belt. Then, using the derived reference site model and 869 recordings, empirical site factors are computed and an empirical site amplification model is regressed. For the earthquakes in the north–south seismic belt, the proposed site amplification model predicts the site amplification for the 50th percentile rotated pseudospectral acceleration (RotD50 SA) with a damping ratio of 5% and periods 0.01–10 s. Moreover, the difference in site amplification factors between the north–south seismic belt of China and those of the Next Generation Attenuation (NGA) database is investigated. In general, variations of site amplification factors of the north–south seismic belt of China with VS30 are less significant than those from the NGA database. Therefore, the regional differences of ground motions caused by site effects are significant for the north–south seismic belt of China. For short periods (<1.0 s) and large values of VS30 (>300 m/s), the median site amplification of the north–south seismic belt is fitted well with most model predictions and the NGA data. The residual regional differences in the north–south seismic belt of China after site corrections can be applied to develop the more efficient global GMMs.
The 2008 Mw 7.9 Wenchuan earthquake, one of the largest continental intraplate events instrumentally recorded, struck the central part of Sichuan Province in southwestern China causing great destruction and loss of life but also providing a wealth of seismological data, geodetic measurements, and tectonic observations. The Wenchuan earthquake ruptured two northwest‐dipping imbricate oblique reverse faults along the middle segment of the Longmenshan fault zone—a northeast‐trending thrust belt located at the boundary between the Tibetan Plateau and the Sichuan Basin. In this study, a hybrid approach that combines deterministic modeling at low frequencies with stochastic modeling at high frequencies is used to simulate broadband ground motions at 52 strong‐motion stations and 506 geodetic sites in the vicinity of the causative fault. The low‐frequency components of the synthetic ground motion are simulated using an extended kinematic source model embedded in a layered medium, whereas the high‐frequency components are generated using a stochastic finite‐fault model. The two independently derived ground‐motion components are then combined using matched filtering at a crossover frequency of 0.8 Hz to generate broadband ground‐motion time histories and response spectra. The temporal and spectral characteristics of the synthetic and recorded ground motions at the 52 strong‐motion stations are compared and the effect of soil nonlinearity on the simulated ground motions is investigated through 1‐D nonlinear site response analysis. Finally, the simulated permanent ground displacements at the 506 geodetic sites are evaluated against geodetic observations and the peak amplitudes of the synthetic ground motions at the same locations are compared with predictions of empirical ground‐motion models.
To make a prediction for seismic signal propagation, one needs to specify physical properties and subsurface ground structure of the site. This information is frequently unknown or estimated with significant uncertainty. This paper describes a methodology for probabilistic seismic ensemble prediction for vertically stratified soils and short ranges with no in situ site characterization. Instead of specifying viscoelastic site properties, the methodology operates with probability distribution functions of these properties taking into account analytical and empirical relationships among viscoelastic variables. This yields ensemble realizations of signal arrivals at specified locations where statistical properties of the signals can be estimated. Such ensemble predictions can be useful for preliminary site characterization, for military applications, and risk analysis for remote or inaccessible locations for which no data can be acquired. Comparison with experiments revealed that measured signals are not always within the predicted ranges of variability. Variance-based global sensitivity analysis has shown that the most significant parameters for signal amplitude predictions in the developed stochastic model are the uncertainty in the shear quality factor and the Poisson ratio above the water table depth.
The study area, Derince town, is one of the most densely industrialized (oil refineries, ports, etc.) and, therefore, populated urban areas located on the North Anatolian Fault Zone in Turkey. The study area is one of the areas that was most affected by the August 17, 1999 Kocaeli Earthquake (Mw = 7.4). A total of 10,984 buildings were heavily damaged, 6131 buildings were moderately damaged, 6803 buildings were slightly damaged and 5239 people were killed during the earthquake. The study area is located on thick sediments and therefore new settlements and industrial facilities have high earthquake hazard. The consequences of any possible earthquake will be very significant for the study area. Therefore, it is important to determine soil properties in earthquake hazard mitigation studies. The seismic vulnerability index (Kg), which depends on resonant frequency, amplification and Vs30 velocity, is a simple but powerful parameter that reflects local soil conditions which affect damage caused by an earthquake. The Kg value shows weak areas of the ground and therefore Kg can be considered to be a vulnerability index for the soil. To obtain Kg characteristics of the study area, the microtremor horizontal-to-vertical spectral ratio (HVSR) method was applied to single site measurements at 43 stations over an area of 40 km². Calculated seismic vulnerability indices were compared with structural damage occurring during the August 17, 1999 Kocaeli Earthquake (Mw = 7.4). The results indicate that the Kg values are in good agreement with damage distribution. Large Kg values indicate weak points in the study area and most of the damage occurred in areas with large Kg values. The areas with Kg values greater than 10 seem to be the most vulnerable locations in the study. Ground conditions should be taken into account during the planning and design of urban areas. The results obtained by considering ground conditions can be used as a quick method to identify risky areas for urban planning.
Earthquake ground motion depends strongly on near‐surface structure, which is challenging to image in urban areas at high resolution. Distributed acoustic sensing (DAS) is an emerging technique that provides a scalable solution by converting preexisting fiber‐optic cables into dense seismic arrays. After the July 2019 M7.1 Ridgecrest earthquake, we converted an underground dark fiber across the city of Ridgecrest, CA, into a DAS array. The recorded aftershocks show substantial lateral variability in site amplification over only 8‐km in distance. To understand the cause of such variability, we used three months of continuous data, dominated by traffic‐generated seismic noise, to image near‐surface structure along the fiber path. We find that the lateral variations of earthquake shaking correlate well with the shallow shear velocity model at sub‐kilometer scales, in particular micro‐basins filled with soft sediments. These results highlight the great potential of DAS for high‐resolution seismic hazard mapping in urban areas.
The Australian territory is just over 400 km from an active convergent plate margin with the collision of the Sunda–Banda Arc with the Precambrian and Palaeozoic Australian continental crust. Seismic energy from earthquakes in the northern Australian plate-margin region are channeled efficiently through the low-attenuation North Australian craton (NAC), with moderate-sized (Mw≥5.0) earthquakes in the Banda Sea commonly felt in northern Australia. A far-field ground-motion model (GMM) has been developed for use in seismic hazard studies for sites located within the NAC. The model is applicable for hypocentral distances of approximately 500–1500 km and magnitudes up to Mw 8.0. The GMM provides coefficients for peak ground acceleration, peak ground velocity, and 5%-damped pseudospectral acceleration at 20 oscillator periods from 0.1 to 10 s. A strong hypocentral depth dependence is observed in empirical data, with earthquakes occurring at depths of 100–200 km demonstrating larger amplitudes for short-period ground motions than events with shallower hypocenters. The depth dependence of ground motion diminishes with longer spectral periods, suggesting that the relatively larger ground motions for deeper earthquake hypocenters may be due to more compact ruptures producing higher stress drops at depth. Compared with the mean Next Generation Attenuation-East GMM developed for the central and eastern United States (which is applicable for a similar distance range), the NAC GMM demonstrates significantly higher short-period ground motion for Banda Sea events, transitioning to lower relative accelerations for longer period ground motions.
We address the relation between seismic local amplification and topographical and geological indicators describing the site morphology. We focus on parameters that can be derived from layers of diffuse information (e.g., digital elevation models, geological maps) and do not require in situ surveys; we term these parameters as “indirect” proxies, as opposed to “direct” indicators (e.g., f0, VS30) derived from field measurements. We first compiled an extensive database of indirect parameters covering 142 and 637 instrumented sites in Switzerland and Japan, respectively; we collected topographical indicators at various spatial extents and focused on shared features in the geological descriptions of the two countries. We paired this proxy database with a companion dataset of site amplification factors at 10 frequencies within 0.5–20 Hz, empirically measured at the same Swiss and Japanese stations. We then assessed the robustness of the correlation between individual site-condition indicators and local response by means of statistical analyses; we also compared the proxy-site amplification relations at Swiss versus Japanese sites. Finally, we tested the prediction of site amplification by feeding ensembles of indirect parameters to a neural network (NN) structure. The main results are: (1) indirect indicators show higher correlation with site amplification in the low-frequency range (0.5–3.33 Hz); (2) topographical parameters primarily relate to local response not because of topographical amplification effects but because topographical features correspond to the properties of the subsurface, hence to stratigraphic amplification; (3) large-scale topographical indicators relate to low-frequency response, smaller-scale to higher-frequency response; (4) site amplification versus indirect proxy relations show a more marked regional variability when compared with direct indicators; and (5) the NN-based prediction of site response is the best achieved in the 1.67–5 Hz band, with both geological and topographical proxies provided as input; topographical indicators alone perform better than geological parameters.
The conversion relation of Site Classes in China building Seismic Code and NEHRP Seismic Provisions is necessary if a Chinese researcher needs to utilize the US earthquake engineering data and research outcomes, vice versa. A serial of studies were carried out in this area. However, some of them stay in the stage of qualitative judgment, some lack in considering the thickness of site overlaying layers (D) which is one of two parameters of determining site class in China Building Seismic Code, some are based on sparse profile data. In this study, based on a database which contains 6,824 borehole profiles, we build the conversion relation of site classes in China Building Seismic Code and NEHRP Seismic Provisions. We first subdivide the China code site classes into more homogeneous sub-classes. We build the probabilistic conversion relations for China code site classes and NEHRP provision site classes. We also find that: (1)It is not appropriate to take the time averaged shear wave velocity to a depth of 20m (VS20) as the proxy for the equivalent shear wave velocity (vse) in site classification of China code; (2)for China code site class II and III, different sub-classes have significantly different corresponding relations with the NEHRP provision site classes; (3)the D effectively distinguishes the sites those velocity structures are similar at shallow layers while different at deeper layers; (4)the main part of China code site class II and III are both corresponding to NEHRP site class D. The China class II leans to the NEHRP class C, while the China class III leans to NEHRP class E; (5)China code site class IV is corresponding to NEHRP site class E; (6)most of NEHRP site class C and D are both corresponding to China code site class II. It implies that the range of China code site class II is relatively vast.(The article uploaded is an English translation and simplified version of a Chinese article published on Acta Seismologica Sinica. )
A depletion of high-frequency ground motions on soil sites has been observed in recent large earthquakes and is often attributed to a nonlinear soil response. Here, I show that the reduced amplitudes of high-frequency horizontal-to-vertical spectral ratios (HVSRs) on soil can also be caused by a smooth crustal velocity model with low shear-wave velocities underneath soil sites. I calculate near-fault ground motions using both 2D dynamic rupture simulations and point-source models for both rock and soil sites. The 1D velocity models used in the simulations are derived from empirical relationships between seismic wave velocities and depths in northern California. The simulations for soil sites feature lower shear-wave velocities and thus larger Poisson’s ratios at shallow depths than those for rock sites. The lower shear-wave velocities cause slower shallow rupture and smaller shallow slip, but both soil and rock simulations have similar rupture speeds and slip for the rest of the fault. However, the simulated near-fault ground motions on soil and rock sites have distinct features. Compared to ground motions on rock, horizontal ground acceleration on soil is only amplified at low frequencies, whereas vertical ground acceleration is deamplified for the whole frequency range. Thus, the HVSRs on soil exhibit a depletion of high-frequency energy. The comparison between smooth and layered velocity models demonstrates that the smoothness of the velocity model plays a critical role in the contrasting behaviors of HVSRs on soil and rock for different rupture styles and velocity profiles. The results reveal the significant role of shallow crustal velocity structure in the generation of high-frequency ground motions on soil sites.
One of the developing areas in Bengkuku City, Indonesia is the downstream of Muara Bangkahulu River. Therefore, this study aims to present an investigation of the local site and analysis of ground response in this area. Geophysical measurements were adopted in this research using multichannel analysis of surface wave and microtremor. Furthermore, field measurements were processed to interpret the characteristics of the ground surface, such as shear wave velocity (Vs) profiles, time-averaged shear wave velocity for the first 30 m depth (Vs30), and site classifications. The results show that the study area is categorised into Site Classes C and D. Also, the loose sedimentary soils exist at shallow depth and tend to be more vulnerable to undergo seismic phenomenon, which includes liquefaction and ground amplification. Generally, the results are expected to provide a better understanding of geophysical characteristics and earthquakes, which will help the local government to compose a spatial plan on the basis of seismic hazard mitigation.
The paper involves the application of the surface geological method for regional site classification in Beijing. Geological maps are collected through GIS to create a relationship of classification between the geological factors of the geological maps and the site classification index of the US NEHRP code. First, the site classification of the US NEHRP is obtained, and based on the relationship of conversion, given by Chinese researchers, between the site classification of the US NEHRP and the China’s Code for Seismic Design of Buildings (GB50011-2010), the results of the site classification of Beijing are obtained based on China’s Code (GB50011-2010). Finally, based on the collected borehole data in Beijing, the results of the site classification map are verified and analyzed.
Newmark analyses of lateral spreading induced by liquefaction were conducted using a database of 22 documented case histories. Site stratigraphy and SPT values for the liquefiable soil were based upon the case-history documentation. The yield acceleration was estimated based on post-liquefaction residual shear strength estimated using three different correlations with SPT blow count. Representative acceleration time histories were selected from time histories recorded in the earthquake. The probabilistic analysis using a truncated normal distribution indicates that the lateral spreading displacement calculated using the Olson and Johnson correlation will be no more than twice the reported displacement with a confidence of 97%.
This article investigates the impacts of the column system on bridge life-cycle costs in high seismic areas. It focuses on hybrid sliding-rocking (HSR) columns, which are an accelerated bridge construction (ABC) technology. The authors conduct a life-cycle cost assessment, quantifying costs of bridge construction and potential earthquake damage and subsequent repairs, as well as the cost of bridge closure time due to construction or repairs. Two prototypical modern seismically designed bridges are considered, each designed with both conventional reinforced concrete (RC) and HSR columns. Construction costs of HSR columns are higher. However, drift demands on the HSR columns are generally lower, damage is less severe and costs of repairing the columns are greatly reduced. Moreover, construction times are about 80% quicker for HSR columns, and repair times are reduced relative to conventional construction. The results suggest substantial advantages to the HSR column system, reducing construction time and expected costs and time for seismic repairs sufficiently to counteract the increase in upfront construction costs. The benefits of the HSR, and by extension other ABC column systems, are particularly significant for highly trafficked bridges in high seismic areas, but hold for a wide range of input assumptions.
A new model of the average shear-wave velocity in the uppermost 30 m was generated by extrapolation of discrete velocity using surface geology at several scales. Statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data; several geologic units with similar responses are grouped together. The resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier, more complicated maps. Analysis within a geographic information system will permit updates and modification of the map as new velocity data are added.
A new theory is presented to study the scattered elastic wave energy propagation in a random isotropic scattering medium. It is based on a scattered elastic wave energy equation that extends the work of Zeng et al. (1991) on multiple scattering by considering S to P and P to S wave scattering conversions. We obtain a complete solution of the scattered elastic wave energy equation by solving the equation in the frequency/wave-number domain. Using a discrete wave-number sum technique combined with a modified repeated averaging and the FFT method, we compute numerically the complete solution. By considering that the scattering conversion from P- to S-wave energy is about (α/β)4 times greater than that from S to P waves (Aki, 1992), we found that the P-wave scattering field was converted quickly to the S-wave scattering field, leading to the conclusion that coda waves generated from both P- and S-wave sources are actually dominated by scattered S waves. We also compared our result with that obtained under the acoustic wave assumption. The acoustic wave assumption for seismic coda works quite well for the scattered S-wave field but fails for the scattered P-wave field. Our scattered elastic wave energy equation provides a theoretical foundation for studying the scattered wave field generated by a P-wave source such as an explosion. The scattered elastic wave energy equation can be easily generalized to an inhomogeneous random scattering medium by considering variable scattering and absorption coefficients and elastic wave velocities in the earth.
In October and November 2001 we performed the first urban shear-velocity transect, across 16 km of the Reno, Nevada area basin. The transect was completed by an average of 3-1/2 people in 9 days employing 45 Reftek RT-125 "Texan" portable recorders mated to 4.5 Hz vertical geophones. The records were analyzed using the refraction microtremor method of Louie (2001). Shear velocity, averaged over 30 meters depth (V 30) is a predictor of earthquake ground motion amplification and potential hazard in similar alluvium-filled basins. V 30 is the basis of site hazard classification under NEHRP-UBC provisions. A simple geologic map-based classification of nearly all of our transect line would be NEHRP-D. Our measurements of V 30 revealed that 82% of the transect is classified NEHRP-C. We also employed the results of a gravity basin-depth study to show that alluvium-depth modeling can be combined with transect V 30 measurements to effectively predict V 30 across the Reno basin. We concluded that unlike the Los Angeles basin, the Reno basin's greatest depths have stiffer, Tertiary sediments underlying the surface. Weaker soils appear to occur east of downtown Reno in the broad floodplain of the Truckee River.
This study determines site-response factors that can be applied as corrections to a rock-attenuation relationship for use in probabilistic seismic-hazard analysis. The site-response factors are amplitude and site-class dependent. These amplification factors are determined by averaging ratios between observed and predicted ground motions for peak ground acceleration (PGA) and for 5% damped response spectral acceleration at 0.3, 1.0, and 3.0 sec oscillator periods. The observations come from the strong-motion database of the Southern California Earthquake Center (SCEC), and the predictions are based on the Sadigh (1993) rock-attenuation relation. When separated and averaged according to surface geology, significantly different site-response factors are found for Quaternary and Mesozoic units, but a subclassification of Quaternary is generally not justified by the data. The low input motion amplification factors are consistent with those obtained from independent aftershock studies at the PGA and 0.3-second period. An observed trend of decreasing Quaternary site amplification with higher input motion is consistent with nonlinear soil behavior; however, the trend exists for Mesozoic sites as well, implying that this may be an artifact of the Sadigh relationship, There is a correlation between larger site-response factors and lower average shear-wave velocity in the upper 30 m for low predicted PGA input motions, with an increase in the correlation with increasing period. The 0.3-sec site response factors for Quaternary data in southern California determined in this study are consistent with 0.3-sec NEHRP site-response correction factors; however, at 1.0-sec period some inconsistencies remain. A trend is also seen with respect to sediment basin depth, where deeper sites have higher average site-response factors. These results constitute a customized attenuation relationship for southern California, The implication of these customized attenuation models with respect to probabilistic hazard analysis is examined in Field and Petersen (2000).
Recent borehole‐geotechnical data and strong‐motion measurements constitute a new empirical basis to account for local geological conditions in earthquake‐resistant design and site‐dependent, building‐code provisions. They provide new unambiguous definitions of site classes and rigorous empirical estimates of site‐dependent amplification factors in terms of mean shear‐wave velocity. A simple four‐step methodology for estimating site‐dependent response spectra is specified herein. Alternative techniques and commentary are presented for each step to facilitate application of the methodology for different purposes. Justification for the methodology is provided in terms of definitions for the new site classes and derivations of simple empirical equations for amplification as a function of mean shear‐wave velocity and input ground‐motion level. These new results provide a rigorous framework for improving estimates of site‐dependent response spectra for design, site‐dependent building‐code provisions, ...
Strong ground motions recorded at 37 sites in the San Francisco Bay region during the Loma Prieta earthquake show marked variations in characteristics dependent on crustal structure and local geologic conditions. Comparative weak- and strong-motion measurements show that mean shear-wave velocity or average low-strain spectral ratios are useful predictors of amplification at the damaging levels of ground motion observed during the earthquake. Analyses suggest that soil amplification and reflected crustal shear energy were major contributors to levels of ground motion sufficient to cause damage to vulnerable structures at distances near 100 km. These strong-motion-amplification factors provide rigorous estimates of amplification for improvements in site-specific design spectra for building-code considerations. -from Authors
Las Vegas Valley has a rapidly growing population exceeding 1.5 mil-lion, subject to significant seismic risk. Surveys of shallow shear velocity performed in the Las Vegas urban area included a 13-km-long transect parallel to Las Vegas Blvd. (The Strip), and borehole and surface-wave measurements of 30 additional sites. The transect was completed quickly and economically using the refraction microtremor method, providing shear velocity versus depth profiles at 49 locations. The lowest velocities in the transect, NEHRP D class, are near intrabasin faults found near Interstate 15 and Lake Mead Blvd. Calcite cementation of alluvium (a.k.a. ca-liche) along the Las Vegas Strip elevates Vs30 values to 500–600 m/sec, NEHRP C class. Our transect measurements correlate poorly against geologic map units, which do not predict the conditions of any individual site with accuracy sufficient for en-gineering application. Some USDA soil map units do correlate, and Vs30 predictions based on measurements of soil units match transect measurements in the transect area. Extending soil-map predictions away from the area of dense measurement cov-erage generally failed to predict new measurements. Further, for several test sites the predictions were not conservative, in that the soil model predicted higher Vs30 than was later measured (predicting lesser potential ground motion). Subsurface infor-mation is needed to build a Vs30 model extending predictions throughout Las Vegas Valley. A detailed stratigraphic model built by correlating 1100 deep well logs in Las Vegas predicts Vs30 better than surface maps, but again only in parts of the Valley well-measured for velocity. The stratigraphic model yields good predictions of our transect Vs30 measurements. It is less accurate, although at least conservative, when extended to sites away from the transect.
This paper describes methods for the predictive mapping of quantities used in the engineering design of earthquake-resistant structures. The most useful such quantities are horizontal response spectral values, but also discussed are peak horizontal acceleration and velocity. An example is given which shows the response spectrum computed for one of the horizontal components of ground motion recorded in the 1979 Imperial Valley earthquake. Refs.
The authors have developed a method for assigning shear-wave velocities to the mapped geologic units in the San Francisco Bay region. In this chapter, the analysis is extended to include the Los Angeles region. Refs.
A number of predictive relationships derived from regression analysis of strong-motion data are available for horizontal peak acceleration, velocity, and response spectral values. Theoretical prediction of ground motion calls for stochastic source models because source heterogeneities control the amplitude of ground motion at most, if not all, frequencies of engineering interest. Theoretical methods have been developed for estimation of ground-motion parameters and simulation of ground-motion time series. These methods are particularly helpful for regions such, as eastern North America where strong-motion data are sparse. The authors survey the field, first reviewing developments in ground-motion measurement and data processing. The authors then consider the choice of parameters for characterizing strong ground motion and describe the wave-types involved in strong ground motion and the factors affecting ground-motion amplitudes. They conclude by describing methods for predicting ground motion.
The effect of alluvium on strong ground motion can be seen by comparing two strong-motion records of the Coyote Lake, California, earthquake of 6 August 1979 (ML = 5.9). One record at a site on Franciscan bedrock had a peak horizontal acceleration of 0.13 g and a peak horizontal velocity of 10 cm/sec. The other, at a site 2 km distant on 180 meters of Quaternary alluvium overlying Franciscan, had values of 0.26 g and 32 cm/sec, amplifications by factors of 2 and 3. Horizontal motions computed at the alluvial site for a linear plane-layered model based on measured P and S velocities show reasonably good agreement in shape with the observed motions, but the observed peak amplitudes are greater by a factor of about 1.25 in acceleration and 1.8 in velocity. About 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance; the remainder may represent focusing by refraction at a bedrock surface concave upward. There is no clear evidence of nonlinear soil response. Fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model. In particular, the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value, indicating that no significant nonlinearity occurs in the secant shear modulus. Computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0.5 to 1.0 or greater. The data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections, and more the simple effect of the low near-surface velocity. Application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear-wave velocity.
The seismic ground motion hazard with site conditions incorporated is mapped for a 10% probability of exceedance in 50 years for the three counties affected by the 1994 Northridge earthquake (Mw 6.7). The source model of Petersen et al. (1996) was used to calculate peak horizontal acceleration (pga) and 5% damped spectral acceleration (SA) levels at 0.3- and 1-sec periods for alluvium, soft-rock, and hard-rock site conditions. A geologic map that differentiates the three site conditions was produced using shear-wave velocity maps of Tinsley and Fumal (1985) and extended into other areas that were not mapped by Tinsley and Fumal using 1:250,000 scale geologic maps. Ground-motion maps for each site condition were overlaid with the geologic map to produce the resulting hazard maps. The effect of geology on the hazard is observed only slightly in the peak ground acceleration map, more in the 0.3-sec SA map, and significantly more in the 1-sec SA map. The uncertainties for ground motions represented on these three maps ranges from 0.1 to 0.3 g for pga and 0.2 to 1.0 for SA; in general, 95% confidence limits are about ± 50% of the mean ground-motion value.
For many earthquake engineering applications, site response is estimated through empirical correlations with the time-averaged shear-wave velocity to 30 m depth (V-S30). These applications therefore depend on the availability of either site-specific V-S30 measurements or V-S30 maps at local, regional, and global scales. Because V-S30 measurements are sparse, a proxy frequently is needed to estimate V-S30 at unsampled locations. We present a new V-S30 map for California, which accounts for observational constraints from multiple sources and spatial scales, such as geology, topography, and site-specific V-S30 measurements. We apply the geostatistical approach of regression kriging (RK) to combine these constraints for predicting V-S30. For the V-S30 trend, we start with geology-based V-S30 values and identify two distinct trends between topographic gradient and the residuals from the geology V-S30 model. One trend applies to deep and fine Quaternary alluvium, whereas the second trend is slightly stronger and applies to Pleistocene sedimentary units. The RK framework ensures that the resulting map of California is locally refined to reflect the rapidly expanding database of V-S30 measurements throughout California. We compare the accuracy of the new mapping method to a previously developed map of V-S30 for California. We also illustrate the sensitivity of ground motions to the new V-S30 map by comparing real and scenario ShakeMaps with V-S30 values from our new map to those for existing V-S30 maps.
In this paper, we have combined the U.S. Geological Survey's National Seismic Hazard Maps model with the California geologic map showing 17 generalized geologic units that can be defined by their V S30. We regrouped these units into seven V S30 values and calculated a probabilistic seismic hazard map for the entire state for each V S30 value. By merging seismic hazard maps based on the seven different V S30 values, a suite of seismic hazard maps was computed for 0.2 and 1.0 s spectral ordinates at 2% probability of exceedance (PE) in 50 years. The improved hazards maps explicitly incorporate the site effects and their spatial variability on ground motion estimates. The spectral acceleration (SA) at 1.0 s map of seismic shaking potential for California has now been published as California Geological Survey Map Sheet 48.
We present an approach based on geomorphometry to predict material properties and characterize site conditions using the V-S30 parameter (time-averaged shear-wave velocity to a depth of 30 m). Our framework consists of an automated terrain classification scheme based on taxonomic criteria (slope gradient, local convexity, and surface texture) that systematically identifies 16 terrain types from 1-km spatial resolution (30 arcsec) Shuttle Radar Topography Mission digital elevation models (SRTM DEMs). Using 853 V-S30 values from California, we apply a simulation-based statistical method to determine the mean V-S30 for each terrain type in California. We then compare the V-S30 values with models based on individual proxies, such as mapped surface geology and topographic slope, and show that our systematic terrain-based approach consistently performs better than semiempirical estimates based on individual proxies. To further evaluate our model, we apply our California-based estimates to terrains of the contiguous United States. Comparisons of our estimates with 325 V-S30 measurements outside of California, as well as estimates based on the topographic slope model, indicate our method to be statistically robust and more accurate. Our approach thus provides an objective and robust method for extending estimates of V-S30 for regions where in situ measurements are sparse or not readily available.
The attenuation relationship presented by Boore et al. (1997) has been evaluated and customized with respect to southern California strong-motion data (for peak ground acceleration (PGA)
and 0.3-, 1.0-, and 3.0-sec period spectral acceleration). This study was motivated by the recent availability of a new site-classification
map by Wills et al. (2000), which distinguishes seven different site categories for California based on the 1994 NEHRP classification. With few exceptions,
each of the five site types represented in the southern California strong-motion database exhibit distinct amplification factors,
supporting use of the Wills et al. (2000) map for microzonation purposes. Following other studies, a basin-depth term was also found to be significant and therefore
added to the relationship. Sites near the center of the LA Basin exhibit shaking levels up to a factor of 2 greater, on average,
than otherwise equivalent sites near the edge. Relative to Boore et al. (1997), the other primary difference here is that PGA exhibits less variation among the Wills et al. (2000) site types. In fact, the PGA amplification implied by the basin-depth effect is greater than that implied by site classification.
The model does not explicitly account for nonlinear sediment effects, which, if important, will most likely influence rock-site
PGA predictions the most. Evidence for a magnitude-dependent variability, or prediction uncertainty, is also found and included
as an option.
In this paper we summarize our recently-published work on estimating horizontal response spectra and peak acceleration for shallow earthquakes in western North America. Although none of the sets of coefficients given here for the equations are new, for the convenience of the reader and in keeping with the style of this special issue, we provide tables for estimating random horizontal-component peak acceleration and 5 percent damped pseudo-acceleration response spectra in terms of the natural, rather than common, logarithm of the ground-motion parameter. The equations give ground motion in terms of moment magnitude, distance, and site conditions for strike-slip, reverse-slip, or unspecified faulting mechanisms. Site conditions are represented by the shear velocity averaged over the upper 30 m, and recommended values of average shear velocity are given for typical rock and soil sites and for site categories used in the National Earthquake Hazards Reduction Program's recommended seismic code provisions. In addition, we stipulate more restrictive ranges of magnitude and distance for the use of our equations than in our previous publications. Finally, we provide tables of input parameters that include a few corrections to site classifications and earthquake magnitude (the corrections made a small enough difference in the ground-motion predictions that we chose not to change the coefficients of the prediction equations).
Consideration of site conditions is a vital step in analyzing and predicting earthquake ground motion. The importance of amplification by soil conditions has long been recognized, but though many seismic-instrument sites have been characterized by their geologic conditions, there has been no consistent, simple classification applied to all sites. As classification of sites by shear-wave velocity has become more common, the need to go back and provide a simple uniform classification for all stations has become apparent. Within the Pacific Earthquake Engineering Research Center's Next Generation Attenuation equation project, developers of attenuation equations recognized the need to consider site conditions and asked that the California Geological Survey provide site conditions information for all stations that have recorded earthquake ground motion in California. To provide these estimates, we sorted the available shear-wave velocity data by geologic unit, generalized the geologic units, and prepared a map so that we could use the extent of the map units to transfer the velocity characteristics from the sites where they were measured to sites on the same or similar materials. This new map is different from the California Geological Survey "preliminary site-conditions map of California" in that 19 geologically defined categories are used, rather than National Earthquake Hazards Reduction Program categories. Although this map does not yet cover all of California, when completed it may provide a basis for more precise consideration of site conditions in ground-motion calculations.
We have used a 3D finite-difference method to simulate ground motion from elastodynamic propagating ruptures with constant slip on faults in the metropolitan area of Los Angeles, California. Simulations are carried out for hypothetical M 6.75 earthquakes on the Palos Verdes and Elysian Park faults and, for comparison, an approximation to the 17 January 1994 M 6.7 Northridge earthquake. The dominant subsurface features of this area are the deep sedimentary Los Angeles basin and the smaller and shallower San Fernando basin. Simulated ground motions are restricted to the frequency range 0.0 to 0.4 Hz. Ground-motion time histories show that, in general, sites associated with the largest particle velocities and cumulative kinetic energies are located (1) in the epicentral area, (2) above the deepest parts of the basins, and (3) near the steepest edges of the Los Angeles basin. We find maximum particle velocities for the Palos Verdes, Elysian Park, and Northridge simulations of 0.44, 0.67, and 0.58 m/sec, respectively. In each case, both the directivity of the rupture and the lower impedance of the basins significantly amplify the ground motion. Although the gross radiation pattern from these ruptures is observable, the 3D basin structure distorts the wave field and becomes a source for edge-generated waves. Signal durations at some basin sites last beyond 90 sec due to Love waves and refracted 5 waves that propagate into the sediments from the basin edges. Compared with the Palos Verdes event, the durations are generally smaller for the Elysian Park earthquake due to a smaller amount of Love waves generated at the basin edges. A simple approximation to the Northridge earthquake reproduces the overall spatial pattern of the long-period particle velocities, successfully predicts the timing of late-arriving waves, and matches the peak velocities with discrepancies generally less than a factor of 2. However, for localized areas immediately north and south of the Santa Monica Mountains, the computed ground motion underpredicts the observed horizontal peak velocities but matches the vertical ones. The pattern of simulated total cumulative kinetic energies is similar to that for the damage intensities observed near the epicenter of the Northridge event. While the Northridge earthquake caused damage in the Los Angeles area, the 3D simulations show that earthquakes with the same magnitude on the Palos Verdes or Elysian Park faults produce more severe ground shaking in the Los Angeles basin.
Site conditions can be classified by the average shear-wave velocity to 30 meters (Vs30) and used for estimating site effects in seismic hazard calculations. Large scale seismic hazard maps, which include site effects, may be produced, providing Vs30 can be well correlated with geologic units. Vs30 values for several geologic units can be easily classified into soil profile types of the UBC (ICBO 1997). Most geologic units have wide variations in Vs30 and some extensive geologic units, such as older alluvium, the Franciscan Complex or the Puente Formation cannot be easily classified.
Ground-motion records from aftershocks of the 1994 Northridge earthquake and mainshock records from the 1971 San Fernando, 1987 Whittier Narrows, 1991 Sierra Madre, and 1994 Northridge earthquakes are used to estimate site response relative to a rock site for the urban Los Angeles area. Site response is estimated at 232 mainshock and 201 aftershock sites relative to a low-amplitude site in the Santa Monica Mountains. Average amplification values are calculated for the frequency bands: 1 to 3, 3 to 5, and 5 to 7 Hz. These bands are chosen based on limitations in aftershock recording equipment at lower frequencies and reduced significance to the building inventory at higher frequencies. Site amplification factors determined at the instrumented locations are grouped by the surficial geology and contoured to produce a continuous spatial estimation of amplification. The maps in this article represent the first attempt to produce estimates of site amplification based on observations of ground motion for such a large areal extent of the Los Angeles region. These maps are expected to evolve as more data become available and more analysis is done.
Rapid (3-5 minutes) generation of maps of instrumental ground-motion and shaking intensity is accomplished through advances in real-time seismographic data acquisition combined with newly developed relationships between recorded ground-motion parameters and expected shaking intensity values. Estimation of shaking over the entire regional extent of southern California is obtained by the spatial interpolation of the measured ground motions with geologically based frequency and amplitude-dependent site corrections. Production of the maps is automatic, triggered by any significant earthquake in southern California. Maps are now made available within several minutes of the earthquake for public and scientific consumption via the World Wide Web; they will be made available with dedicated communications for emergency response agencies and critical users.
Shear-wave velocities of shallow surficial geologic units were measured at 210 sites in a 140-km2 area in the greater Oakland, California, area near the margin of San Francisco Bay. Differences between average values of shear-wave velocity for each geologic unit computed by alternative ap- proaches were in general smaller than the observed variability. Averages es- timated by arithmetic mean, geometric mean, and slowness differed by 1 to 8%, while coefficients of variation ranged from 14 to 25%. With the excep- tion of the younger Bay mud that underlies San Francisco Bay, velocities of the geologic units are approximately constant with depth. This suggests that shear-wave velocities measured at different depths in these surficial geologic units do not need to be normalized to account for overburden stress in order to compute average values. The depth dependence of the velocity of the younger Bay mud most likely is caused by consolidation. Velocities of each geologic unit are consistent with a normal statistical distribution. Average values increase with geologic age, as has been previously reported. Velocities below the water table are about 7% less than those above it. (DOI: 10.1193/1.1852561)
We have evaluated two methods of estimating linear site-response amplifications and the standard index for classifying sites by comparing the results of each technique to observed ground motions at 33 sites in the Los Angeles region. Using velocity and density profiles from 33 boreholes, we evaluated the use of the average 30-m shear-wave velocity and associated site classifications, the quarter-wavelength method, and the Haskell propagator matrix method. We correlated the average 30-m shear-wave velocity and NEHRP site classification at the borehole sites colocated within 290 m of a site with observed ground motion. The observed data follow the expected trend of higher ground-motion amplifications for lower average shear-wave velocities, but there is a significant degree of variability. Also, there is a great deal of scatter in the observed amplifications within each National Earthquake Hazards Reduction Program (NEHRP) class. We used the velocity and density information in the database to calculate the average frequency-dependent site response in the frequency ranges 1-3 Hz, 3-5 Hz, and 5-7 Hz for a one-dimensional flat-layered structure using the Haskell propagator matrix method and the quarter-wavelength method. There is a general correlation with the ground-motion data; however, once again there is a great degree of scatter, although slightly less for the quarter-wavelength method. We note that both the observed and predicted amplifications can change dramatically over a distance as small as 1 km or less. Even though all techniques considered give results that follow the expected trend of higher amplifications for softer sediments, the "predicted" site response at any particular site with the current level of information may not be representative of the shaking that will actually occur during an earthquake. The disparity between observed and predicted amplifications appears to be a result of oversimplification inherent in the amplification-estimation methods, such as the use of average or assumed values for the site conditions in the absence of measured values, the "smoothing" effect of using an average velocity, limiting the properties considered to the uppermost 30 m of material, and complexities in the wave propagation that are not addressed by these methods.
We describe a technique to derive first-order site-condition maps di-rectly from topographic data. For calibration, we use global 30 arc sec topographic data and V S 30 measurements (here V S 30 refers to the average shear-velocity down to 30 m) aggregated from several studies in the United States, as well as in Taiwan, Italy, and Australia. V S 30 values are correlated against topographic slope to develop two sets of parameters for deriving V S 30 : one for active tectonic regions where to-pographic relief is high, and one for stable shields where topography is more subdued. By taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear-velocity observations, we can recover, to first order, many of the spatially varying features of site-condition maps developed for California. Our site-condition map for the low-relief Mississippi Embayment also predicts the bulk of the V S 30 observations in that region despite rather low slope ranges. We find that maps derived from the slope of the topography are often well cor-related with other independently derived, regional-scale site-condition maps, but the latter maps vary in quality and continuity, and subsequently, also in their ability to match observed V S 30 measurements contained therein. Alternatively, the slope-based method provides a simple approach to uniform site-condition mapping. After validating this approach in regions with numerous V S 30 observations, we subsequently estimate and map site conditions for the entire continental United States using the respective slope correlations.
The late Jurassic and Cretaceous Eastern Franciscan belt of the northern California Coast Range consists of two multiply deformed, blueschist-facies terranes; the Pickett Peak and Yolla Bolly terranes. Four deformations have been recognized in the Pickett Peak terrane, and three in the Yolla Bolly terrane. The earliest recognized penetrative fabric, D1, occurs only in the Pickett Peak terrane. The later penetrative fabrics, D2 and D3, occur in both the Yolla Bolly and Pickett Peak terranes. D1 and D2 apparently represent fabrics that formed during subduction and accretion of the terranes. Fabrics from both D1 and D2 are consistent with SW-NE movement directions with respect to their present geographic positions. D3 postdates blueschist-facies metamorphism of the terranes and may be related to emplacement of the terranes to higher structural levels. A broad regional warping, D4, is evident from the map pattern and folding of large metamorphosed thrust sheets. D4 folds may be related to deformation associated with oblique convergence along the continental margin in late Cretaceous and (or) early Tertiary time.
A urinary luteinizing hormone (LH) test (LH Color, Organon, Oss, The Netherlands), was used to time intrauterine insemination in 177 cycles. Morning and evening urine samples were tested. In 58 women (33%) the test was positive in the morning urine sample. Fifteen of these patients were inseminated 8-10 h thereafter and one patient (6.7%) conceived. The remaining 43 women were inseminated the following day, 25-31 h after LH detection, and seven pregnancies (16.3%) ensued. In 119 cycles showing a positive urinary test in the evening sample, insemination was performed the next day, between 17 and 23 h after the LH surge, and 18 patients (15.1%) became pregnant. Statistical analysis showed no significant differences in pregnancy rates between the three different schedules, or in the time of insemination between conceptional and non-conceptional cycles within each group. Most ovulations occurred between 16 and 28 h after the positive test was observed. These findings suggest that while the lifespan of the gametes allows a relatively long period for fertilization, from 8 to 31 h after urinary LH surge detection, better results may be expected when inseminating about 24 (+/- 6) h after the positive test.
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