No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Shear-Wave Velocity Characteristics of Geologic Units in California
Abstract
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.
... Surface-geology-derived classification schemes have been used to produce regional V S site-condition maps based on rock type and/or geological age (e.g., Tinsley and Fumal, 1985;Park and Elrick, 1998;Wills and Silva, 1998). The correlation between V S and geologic units relies on the fact that V S depends on physical properties of the materials, such as density, porosity, cementation, and fracture spacing. ...
... The correlation between V S and geologic units relies on the fact that V S depends on physical properties of the materials, such as density, porosity, cementation, and fracture spacing. Wills and Silva (1998) correlated V S30 data with geologic units in California and extrapolated based on surface geology to obtain a statewide map of V S30 . That approach has been further refined using depositional environment and geographic criteria as additional constraints (Wills et al., 2000;Wills and Clahan, 2006). ...
... Park and Elrick (1998) developed a geologically based (V S30 ) map for the southern California region. Their approach differs from that of Wills and Silva (1998) in that their goal was to achieve the simplest model supported by the dataset. To attain that objective, they used statistical tests (the t-test and the Kolmogorov-Smirnov test) to justify the subdivision of an initial set of geological units, if statistically significant. ...
The inclusion of site-specific conditions is essential to adequately represent the seismic hazard and the seismic risk for a region. We acquired, gathered, and organized a near-surface shear-wave velocity database for Portugal and applied a three-step methodological approach for developing a VS30 site-condition map using extrapolation based on surface geology. The methodology includes (1) defining a preliminary set of geologically defined units, (2) calculating the probability distribution of log VS30 for each unit, and (3) merging the units according to the results of statistical tests. The final model comprises three geologically defined units characterized by log VS30 distributions that are statistically significantly different from each other: F1, igneous, metamorphic, and old sedimentary rocks; F2, Neogene and Pleistocene formations; and F3, Holocene formations. The site conditions for the F3 unit may be further refined using correlations with topographic slope based on the Shuttle Radar Topography Mission at 3 arcsec resolution (SRTM3) dataset. We analyzed the performance site-condition models based on correlations with exogenous data (topographic slope and surface-geology analogs). The results show that the residual distributions between log VS30 values measured and estimated from those proxies are strongly biased for some geological units, emphasizing the need for acquiring regional VS data.
... Given the investigation frequencies, our results have important and practical implications for fields interested in the near surface. This includes earthquake hazard mapping because low-velocity features tend to indicate regions susceptible to strong ground motion during earthquake-related shaking (Wills and Silva, 1998). ...
... Another prominent feature in both group velocity maps is a low-velocity zone in the southeast region of the array. This zone corresponds to Alamitos Bay, and the geologic map indicates that it was built on artificial fill, which is expected to display relatively low velocities (Wills and Silva, 1998). Overall, the significant trends in our group velocity maps match the surface geology at Long Beach well. ...
... Overall, our results can benefit fields interested in the near surface, such as earthquake hazard analysis. Shear velocity is proportional to the impedance of the material, and seismic wave amplitudes typically increase with lower impedance (Wills and Silva, 1998). Thus, regions with low shear velocity (and hence low impedance) at shallow depths are more susceptible to earthquake-induced damage than regions with high shear velocity. ...
Using a dense seismic array in Long Beach, California, we have investigated the effectiveness of using traffic noise for passive subsurface imaging. Spectral analysis revealed that traffic-induced vibrations dominate the ambient seismic noise field at frequencies between 3 and 15 Hz. Using the ambientnoise crosscorrelation technique at these frequencies, we have extracted fundamental- and first-order-mode Rayleigh waves generated by Interstate 405 and local roads. We picked group traveltimes associated with the fundamental mode and used them in a straight-ray tomography procedure to produce group velocity maps at 3.0 and 3.5 Hz. The velocity trends in our results corresponded to shallow depths and coincided well with lithologies outlined in a geologic map of the survey area. The most prominent features resolved in our velocity maps were the low velocities to the north corresponding to less-consolidated materials, high velocities to the south corresponding to more-consolidated materials, a low-velocity zone corresponding to artificial fill in Alamitos Bay, and a low-velocity linear feature in the Newport-Inglewood Fault Zone. Our resulting near-surface velocities can be useful for identifying regions that are susceptible to serious damage during earthquake-related shaking.
... Surface-geology-derived classification schemes have been used to produce regional V S site-condition maps based on rock type and/or geological age (e.g., Tinsley and Fumal, 1985;Park and Elrick, 1998;Wills and Silva, 1998). The correlation between V S and geologic units relies on the fact that V S depends on physical properties of the materials, such as density, porosity, cementation, and fracture spacing. ...
... The correlation between V S and geologic units relies on the fact that V S depends on physical properties of the materials, such as density, porosity, cementation, and fracture spacing. Wills and Silva (1998) correlated V S30 data with geologic units in California and extrapolated based on surface geology to obtain a statewide map of V S30 . That approach has been further refined using depositional environment and geographic criteria as additional constraints (Wills et al., 2000;Wills and Clahan, 2006). ...
... Park and Elrick (1998) developed a geologically based (V S30 ) map for the southern California region. Their approach differs from that of Wills and Silva (1998) in that their goal was to achieve the simplest model supported by the dataset. To attain that objective, they used statistical tests (the t-test and the Kolmogorov-Smirnov test) to justify the subdivision of an initial set of geological units, if statistically significant. ...
The Probabilistic Seismic Hazard Map of Portugal is being prepared under the project SCENE - "Site Condition Evaluation for National Seismic Hazard Estimation". The project is developing a VS,30 database for Portugal, which started by gathering the geologic; geotechnical and geophysical data available in the literature. The detailed geologic and seismic characterization of 30 sites of the Portuguese strong motion network. The sites to be characterized are mainly concentrated in the southern area of Portugal because of the higher site effects felt in these regions in previous earthquakes. The Tagus valley and the Algarve are the areas to be studied in more detail. MASW testing was used in 7 strong-motion sites, mainly to characterize the sites with soft soils (Holocene and Pliocene deposits). Some results of MASW VS,30 determinations in the Tagus valley region are presented here.
... Park and Elrick (1998) showed that V S30 varies with grain size and age, and accordingly grouped the geologic units in southern California into eight different categories. Similarly, Wills and Silva (1998) assembled a database of shear-wave velocity measurements and correlated those with the materials described in borehole logs. Wills et al. (2000) published a site-condition map for all of California based on the National Earthquake Hazards Reduction Program (NEHRP) V S30 categories, correlation of geologic units with V S30 from Wills and Silva (1998), and generalization of the statewide 1:250,000-scale geologic maps. ...
... Similarly, Wills and Silva (1998) assembled a database of shear-wave velocity measurements and correlated those with the materials described in borehole logs. Wills et al. (2000) published a site-condition map for all of California based on the National Earthquake Hazards Reduction Program (NEHRP) V S30 categories, correlation of geologic units with V S30 from Wills and Silva (1998), and generalization of the statewide 1:250,000-scale geologic maps. The preliminary site-condition map of Wills et al. (2000) was found to correlate with seismic amplification (Field, 2000) and represented a credible first approximation for consideration of site conditions in seismic-hazard estimates. ...
... More recent work by Wills and Clahan (2006) attempted to outline areas corresponding to geologic units with distinct V S30 . This effort provided an estimate of V S30 for use in the Pacific Earthquake Engineering Research Center's Next Generation Attenuation (NGA) equation project by applying the shear-wave velocity characteristics of geologic units, similar to the units described by Wills and Silva (1998), to all sites in the NGA database. This effort resulted in a set of 17 generalized geologic units that can be described by their shear-wave velocity and a map of California showing those units. ...
Correlations between geologic units and shear wave velocity form the basis of a series of maps developed over the past 15 years to estimate average shear-wave velocity to 30m (Vs30). Wills et al.’s (2000) site-condition map for California was found to correlate with seismic amplification (Field, 2000) and was adopted as a standard depiction for many applications of seismic shaking estimates (ShakeMap for example). Wills and Clahan (2006) modified that map to show simplified geologic units and corresponding Vs30 values. Preparation of this map raised a number of questions on how best to distinguish units within younger alluvium. Wills and Gutierrez (2011) found that a simple system based on surface slope could be used to subdivide the younger alluvium into three classes that have distinct Vs30 ranges. The classes defined by slope have approximately the same variability in Vs30 as the previously defined classes, but the total number of classes is reduced and the system can be easily applied to other tectonically active areas. We have now applied the system of Wills and Gutierrez (2011) to create a new map of California using the most detailed available geologic maps. Use of more detailed geologic maps, from 1:250,000 scale to 1:24,000 for much of California, results in a much more detailed and accurate depiction of the surficial geology and, we anticipate, a more detailed and accurate depiction of seismic amplification due to the near-surface materials.
... The geologic units are then assigned to shear-wave velocity categories. Correlation of geologic units with V s 30 values is guided by shear-wave velocity measured in over a thousand shallow boreholes (generally about 30 m deep) statewide, mostly in the San Francisco Bay and Los Angeles metropolitan areas (Wills and Silva, 1998). This map represents a first cut at systematically classifying site-conditions across the state with parameters that have been correlated with strong ground-motion amplification (Borcherdt, 1994;Martin and Dobry, 1994). ...
... Older (Pleistocene) and coarse alluvial units have V s 30 values ranging from about 300 to 400 m/sec. Younger (Holocene) medium-and fine-grained units have V s 30 values from about 200 to 320 m/sec (Wills and Silva, 1998). Accordingly, younger alluvium is classified D on our map except where it is known to be notably coarsegrained and the boundaries of an area of coarse young alluvium were shown on the regional maps that we used in our compilation. ...
... In the Franciscan Complex in the San Francisco Bay Area, the shear-wave velocity commonly depends on the lithology and on the amount of shearing. The V s 30 values are highly variable (Wills and Silva, 1998) and do not fit into any V s category. Of the 18 profiles that fall within the map BC but have values outside the range for that category, nine are from the ...
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.
... The geologic-based site categories defined in this study can be approximately related to the average shear-wave velocity in the top 30 m of the site, V S30 , based on statistical analyses of measured V S30 for similar geologic units reported by Wills and Silva (1998) and Wills et al. (2000) for all of California and by Park and Elrick (1998) for southern California. These relationships are summarized in Table 3. ...
... Three observations are clear from this table: (1) there is considerable variability in the mean estimates of V S30 among the different compilations, although these differences are not necessarily statistically significant; (2) the standard deviation of an individual estimate of V S30 for a given site category varies anywhere from about 20% to 35% of its mean value; and (3) the mean value of V S30 for some studies and categories are based on a relatively small number of measurements. For the more robust Wills and Silva (1998) study, velocities are given for the two major geologic units of our firm rock category, namely, crystalline rock (located primarily in southern California) and Franciscan Complex (located primarily in northern California). A hypothesis test of the difference in the means of the Wills and Silva (1998) velocities for the different site categories listed in Table 3 indicated that the hypothesis that this difference is zero can be rejected at the 5% level of significance for all categories, except for the comparison between crystalline rock and Franciscan Complex. ...
... For the more robust Wills and Silva (1998) study, velocities are given for the two major geologic units of our firm rock category, namely, crystalline rock (located primarily in southern California) and Franciscan Complex (located primarily in northern California). A hypothesis test of the difference in the means of the Wills and Silva (1998) velocities for the different site categories listed in Table 3 indicated that the hypothesis that this difference is zero can be rejected at the 5% level of significance for all categories, except for the comparison between crystalline rock and Franciscan Complex. Therefore, we suggest that the means and standard deviations of V S30 given by Wills and Silva (1998) can be used as reasonable estimates of the velocities for the four site categories defined in our study. ...
In this study we used strong-motion data recorded from 1957 to 1995 to derive a mutually consistent set of near-source horizontal and vertical groundmotion (attenuation) relations for peak ground acceleration and 5%-damped pseudo-acceleration response spectra. The database consisted of up to 960 uncorrected accelerograms from 49 earthquakes and 443 processed accelerograms from 36 earthquakes of N-w 4.7-7.7. All of the events were from seismically and tectonically active, shallow crastal regions, located throughout the world. Some major findings of the study are (1) reverse- and thrust-faulting events have systematically higher amplitudes at. short periods, consistent with their higher dynamic stress drop; (2) very firm soil and soft rock sites have similar amplitudes, distinctively different from amplitudes on firm soil and firm rock sites; (3) the greatest differences in horizontal ground motion among the four site categories occur at long periods on firm rock sites, which have significantly lower amplitudes due to an absence of sediment amplification, and at short periods on firm soil sites, which: have relatively low amplitudes at large magnitudes and short distances due to nonlinear site effects; (4) vertical. ground motion exhibits similar behavior to horizontal motion for firm rock sites at long periods but has. relatively higher short-period amplitudes at short distances on firm soil sites due to a lack of nonlinear site effects, less anelastic attenuation, and phase conversions within the upper sediments. We used a relationship similar to that of Abrahamson and Silva (1997) to model hanging-wall effects but found these effects to be important only for the firmer site categories. The ground-motion relations do not include recordings from the 1999 M-w > 7 earthquakes in Taiwan and Turkey because there is, still no consensus among strong-motion seismologists as to why these events had such low ground motion. If these near-source amplitudes are later found to be atypical, their inclusion could lead to unconservative engineering estimates of ground motion. The study is intended to be a limited update of the ground-motion. relations previously developed. by us in 1994 and 1997, with the explicit purpose of providing engineers and seismologists with a mutually consistent set of near-source ground-motion relations to use in seismic hazard studies. The U.S. Geological Survey and the California Geological Survey have selected the updated relation as one of several that they are using in their 2002 revision of the U.S. and California seismic hazard maps. Being a limited update, the study does not explicitly address such topics as peak ground velocity, sediment depth, rupture directivity effects, or the use of the 30-m velocity or related National Earthquake Hazard Reduction Program site classes. These are topics of ongoing research and will be addressed in a future update.
... Although this more refined geological classification has not been utilized in most attenuation relations, Campbell and Bozorgnia [in press] clearly demonstrated the importance of this classification scheme in the prediction of near-source ground motion. Park and Elrick [1998] and Wills and Silva [1998] have also shown that a more refined geological classification is warranted based on measurements of shear-wave velocity in various geologic units in California. ...
... The relation accounts for site response through the 30-m velocity V S30 . Some typical values for V S30 are provided in Tables 5.2 and 5.4 [see also Wills and Silva, 1998]. This parameter must be set to some value in order for the prediction to be valid. ...
Only engineering models that directly predict ground-motion amplitude or that predict the modulation of this amplitude from such effects as fault geometry and source directivity are discussed in this chapter. Duration is an important aspect of strong ground motion, especially for the inelastic response of structures, but much less attention has been paid to predicting duration and, therefore, no consensus engineering models are available. Generally speaking, the inelastic behavior of structures is included in structural design through the use of time histories and structural ductility factors, which are the topics of other chapters in this book.
... Measuring V s30 at a regional scale, however, is practically and economically not feasible. This has led to attempts to use geology, geomorphology, and topography as a proxy for geotechnical properties and regolith thickness providing thereby means for estimating V s30 at a regional scale (Wills and Silva 1998;Wills et al. 2000;Matsuoka et al. 2005;Shafiee and Azadi 2007;Thompson et al. 2007;Wald and Allen 2007;Yong et al. 2008;Shafique et al. 2012). The control of underlying geological units on estimated V s30 was observed by Wills et al. (2000), Wills and Clahan (2006), and Shafiee and Azadi (2007). ...
... Contrary to topography, significant control of the underlying geology on the estimated V s30 is observed in the study area, as was previously observed by Wills and Silva (1998), Wills et al. (2000), Wills and Clahan (2006), and Shafiee and Azadi (2007). Within each geological formation, variation in V s30 is (Fig. 7). ...
Earthquakes, with their unpredictable and devastating nature, have resulted in large damages worldwide. Seismic site characterization maps (SSCMs) are frequently and effectively used to demarcate the locations that are prone to amplified seismic response. The time-averaged shear wave velocity of top 30 m of earth surface (Vs30) is effectively used as a parameter to evaluate seismic amplification. Northern Pakistan is one of the most seismically active region in the world with 2005 Kashmir earthquake as the most devastating natural disaster. However, for most of the country, the seismic site characterization maps are not available. Geological units and topographic slope are used as proxies for Vs30-based SSCMs around the world and in northern Pakistan. However, the studies in northern Pakistan are lacking field-based validation of the estimated Vs30 and hence the proxy-based SSCMs might be unrealistic. The aim of this study is to correlate instrument-based Vs30 measurements with geological units and remote sensing-derived topographic slope to develop a more realistic SSCM for the study area, located in the seismically active northern Pakistan. Geology of the study area has significant impact on the estimated Vs30 and hence is used as a proxy for SSCM. The developed SSCM shall assist in developing earthquake mitigation strategies in the region.
... Although this more refined geological classification has not been utilized in most attenuation relations, Campbell and Bozorgnia [in press] clearly demonstrated the importance of this classification scheme in the prediction of near-source ground motion. Park and Elrick [1998] and Wills and Silva [1998] have also shown that a more refined geological classification is warranted based on measurements of shear-wave velocity in various geologic units in California. ...
... The relation accounts for site response through the 30-m velocity V S30 . Some typical values for V S30 are provided in Tables 5.2 and 5.4 [see also Wills and Silva, 1998]. This parameter must be set to some value in order for the prediction to be valid. ...
... Kayen, 2012, written commun.). Based on numerous empiri- cal studies (Borcherdt and Gibbs, 1976;Borcherdt, 1994;Wills and Silva, 1998), Vs30 has become the most common means of classifying site conditions (soil class) and has been adopted in the National Earthquake Hazard Reduction Program (NEHRP) design provisions for new buildings (Martin, 1994). Because surface Vs30 measurements are sparse, proxy methods are often used to estimate Vs30 and soil class at most locations for USGS earthquake assessment and hazard products such as Shakemap and the national seismic hazard map. ...
... In Figure 7 we also determine how well our HVSR peak frequency proxy relationship predicts Vs30 measured at the sur- face. We estimate Vs30 at 21 seismic stations with clear HVSR based on broad soil classes that are most commonly defi ned by the average shear-wave velocity in the upper 30 m (Vs30) (Martin, 1994;Borcherdt, 1994;Wills and Silva, 1998). High Vs30 values are associated with fi rm, dense rock and lower levels of ground shaking, while lower Vs30 values are associated with softer soils and site amplifi cation of 1.5-2 ( Petersen et al., 2008). ...
Earthquake damage is often increased due to local ground-motion amplifi cation caused by soft soils, thick basin sediments, topographic effects, and liquefaction. A critical factor contributing to the assessment of seismic hazard is detailed information on local site response. In order to address and quantify the site response at seismograph stations in the eastern United States, we investigate the regional spatial variation of horizontal:vertical spectral ratios (HVSR) using ambient noise recorded at permanent regional and national network stations as well as temporary seismic stations deployed in order to record aftershocks of the 2011 Mineral, Virginia, earthquake. We compare the HVSR peak frequency to surface measurements of the shearwave seismic velocity to 30 m depth (Vs30) at 21 seismograph stations in the eastern United States and fi nd that HVSR peak frequency increases with increasing Vs30. We use this relationship to estimate the National Earthquake Hazards Reduction Program soil class at 218 ANSS (Advanced National Seismic System), GSN (Global Seismographic Network), and RSN (Regional Seismograph Networks) locations in the eastern United States, and suggest that this seismic station-based HVSR proxy could potentially be used to calibrate other site response characterization methods commonly used to estimate shaking hazard.
... A microzonation of the two towns was conducted to explain such differences. The mean value of the shear-wave velocity (Vs) in the first 30 m (Vs30) is a universally accepted parameter for soil classification (Borcherdt and Glassmoyer 1992;Anserson et al. 1996;FEMA 1997;Wills and Silva 1998;Eurocode-8 1998) and is directly related to soil stiffness; likewise, the impedance contrast is also related to the seismic amplification. ...
... The mean value of the shear-wave velocity (Vs) in the first 30 m (Vs30) is a parameter that is universally accepted in soil classification (Borcherdt and Glassmoyer 1992;Anserson et al. 1996; Federal Emergency Management Agency (FEMA) 1997; Wills and Silva 1998;Eurocode-8 1998). Vs is directly related to soil stiffness, and the impedance contrast is also related to the seismic amplification. ...
The recent seismic activity recorded in Jaén province in the southeast Iberian Peninsula has triggered great alarm among the people of the towns of Torreperogil and Sabiote despite the low magnitude of the events. The main objective of this paper is to examine why these low magnitude events are responsible for such a high degree of concern in this area of low seismicity. Of all possible explanations, including directivity effects and local geology, we found that the site effect was the most important candidate for clarifying this phenomenon.
An earthquake scenario was considered for the maximum 5.2 Mw shock that could occur in the event of the rupture of the identified responsible blind fault. In order to simulate the strong motion derived from such as extreme event, a stochastic finite fault simulation was generated using the standard values of the different media parameters for the region and a stress drop of 130 bar, deduced from the simulation of the greatest shock of the sequence.
In order to include the site effect, which was considered to be very important in this study, a local survey using refraction micro-tremor (ReMi) techniques was performed in both towns (at 33 and 35 sites in Torreperogil and Sabiote, respectively) to determine the Vs30 values. The site response results obtained were taken into account in the simulation process and the results are shown on peak ground acceleration (PGA) and peak ground velocity (PGV) contour maps for each town, with 200–500 cm/s2 as PGA extreme values. A map of intensities obtained from the PGV map is also shown; for the extreme event, macroseismic EMS98 intensities in the range of V to VII, were obtained for those towns.
The deterministic earthquake scenario developed here will be of great interest in planning civil defense responses in the event of an earthquake emergency and in regional development.
... This limits the number of locations where such data are available. Researchers have addressed this need primarily by developing spatial models to predict site class or spectral amplifications at unsampled locations (Tinsley and Fumal, 1985; Wills and Silva, 1998; Wills et al., 2000; Holzer et al., 2005; Wills and Clahan, 2006; Wald and Allen, 2007; Yong et al., 2008). Three of these methods are similar in scale to this study. ...
... The Wills and Silva (1998), Wills et al. (2000, and Wills and Clahan (2006) method for predicting V s (30) is based on previously mapped surficial geologic units. The underlying assumption of this method is that V s , or at least V s (30), is approximately homogeneous within the spatial extent of surficial geologic units. ...
We describe an approach to model liquefaction extent that focuses on identifying broadly available geospatial variables (e.g., derived from digital elevation models) and earthquake-specific parameters (e.g., peak ground acceleration, PGA). A key step is database development: We focus on the 1995 Kobe and 2010-2011 Christchurch earthquakes because the presence/absence of liquefaction has been mapped so that the database is unbiased with respect to the areal extent of liquefaction. We derive two liquefaction models with explanatory variables that include PGA, shear-wave velocity, compound topographic index, and a newly defined normalized distance parameter (distance to coast divided by the sum of distance to coast and distance to the basin inland edge). To check the portability/reliability of these models, we apply them to the 2010 Haiti earthquake. We conclude that these models provide first-order approximations of the extent of liquefaction, appropriate for use in rapid response, loss estimation, and simulations.
... Reliable shallow shear (SH)-wave velocity (V S ) information is often a critical need for improving site response estimation, ground-motion investigations, and seismic hazard modeling. The time-averaged shear-wave velocity to a depth of 30 m (V S30 ) is a current standard for characterizing site effects in seismic hazard models, building codes (International Code Council, 2015), and earthquake engineering design applications (Borcherdt, 1994;Kramer, 1996;Wills and Silva, 1998;Dobry et al., 2000). Although V S30 is the standard for these efforts, it is not universally accepted as an optimal parameter on which to evaluate site response (Castellaro et al., 2008;Di Alessandro et al., 2012), thus leading to efforts to seek a better site parameter. ...
We analyze multimethod shear (SH)-wave velocity (VS) site characterization data acquired at three permanent and 25 temporary seismograph stations in Oklahoma that recorded M 4+ earthquakes within a 50 km hypocentral distance of at least one of the 2016 M 5.1 Fairview, M 5.8 Pawnee, or M 5.0 Cushing earthquakes to better constrain earthquake ground-motion modeling in the region. We acquired active-source seismic data for time-averaged VS to 30 m depth (VS30) at 28 seismograph stations near the Fairview, Pawnee, and Cushing epicentral areas. The SH-wave refraction travel times coupled with Rayleigh- and Love-wave phase velocity dispersion were extracted and modeled in a nonlinear least-squares (L2) joint inversion to obtain a best-fit 1D VS versus depth profile for each site. At a subset of sites where the preferred L2 inverse model did not optimally fit each of the Love, Rayleigh, and SH travel-time datasets, we explore application of simulated annealing in a joint inversion to find a more global solution. VS30 values range from 262 to 807 m/s for the preferred measured (in situ) VS profiles, or National Earthquake Hazards Reduction Program (NEHRP) site class D to B, and are broadly comparable with estimates from previous data reports in the region. Site amplification estimates were calculated next from 1D SH transfer functions of the preferred VS profiles and then compared against observed horizontal-to-vertical spectral ratios (HVSRs) from nearby seismograph stations. We generally see good agreement between the predicted in situ model and the observed HVSR resonant frequencies, with nominal amplifications between 2 and 10 within the 2–15 Hz frequency band. Next, using 40 known in situ VS30 measurements in the region, we demonstrate that the in situ VS30 values improve the fit for selected suites of ground-motion models (GMMs) for M 4+ earthquakes within a 50 km hypocentral distance when compared with proxy methods, arguing for future development of GMMs implementing in situ VS profiles.
... We utilized the recordings of 83 stations from AFAD and 10 stations from KOERI that are located in the region where shaking was relatively stronger. The region considered in this study as well as the AFAD and KOERI strong-motion stations of interest are illustrated in Fig. 2. All AFAD stations have measured V S30 values (time-based average of shear wave velocity profile of the uppermost 30 m) to characterize their site conditions but the site characterization of KOERI stations are proxy V S30 values that we inferred from the shear wave velocity characteristics of regional geological units (Wills and Silva 1998). ...
We assess the significance of rupture-plane uncertainty in the estimated ground-motion intensity measures (IMs) by using the centroid moment-tensor and fault-plane solutions as well as the ground-motion recordings of the 30 October 2020 Samos Earthquake. We sampled ground-motion fields using stochastically generated rupture planes by considering the uncertainties imposed from alternative fault-plane solutions to reach our objective. Our observations indicate that the compromise between rupture-plane uncertainty and variability in the predicted ground-motion IMs depends on the modeling complexity of the ground-motion predictive model (GMPM). It also depends on the spatial location of the site relative to the ruptured fault. This conclusive remark is important for modelers who perform regional or site-specific seismic hazard and risk analyses. The presented case studies are also useful for GMPM developers because the ground-motion models contain predictor parameters, the most ubiquitous one is source-to-site distance, that are affected from rupture-plane geometry. Depending on the level of model complexity, the number of predictor parameters affected from rupture-plane geometry can increase and therefore the estimated ground-motion IMs can become more prone to rupture-plane uncertainty. Confined to our case-specific observations, we intend to make some suggestions to hazard, risk, and GMPM modelers for the consideration of rupture-plane uncertainty at the end of the paper.
... The region considered in this study as well as the AFAD and KOERI strong-motion stations of interest are111 illustrated in Figure 2. All AFAD stations have measured VS30 values (time-based average of shear wave velocity 112 profile of the uppermost 30 m) to characterize their site conditions but the site characterization of KOERI stations 113are proxy VS30 values that we inferred from the shear wave velocity characteristics of regional geological units 114(Wills and Silva, 1998). ...
... The proxy methods have been basically developed to address this requirement. Many studies such as Wills and Silva (1998) and Wills and Clahan (2006) correlate the V S30 with geologic units. In these studies, it is assumed that V S30 is dependent to the physical properties of soil. ...
This paper provides a review of the procedure of customizing ShakeMap V4.0 provided by U.S. Geological Survey based on seismic characteristics of Iran. Selecting appropriate GMPEs, adopting a suitable spatial cross-correlation model and proper modeling of site condition are important factors in the context of the ShakeMap algorithm. The present paper technically reviews the aforementioned parameters. In addition, a number of statistical tests were performed to provide the optimum configuration. The initial prototype of the configured ShakeMap has been used to provide the ground motion shaking map in the aftermath of a great earthquake in Iran (since Aug, 2021).
... Seismic site characterisation maps for seismic site conditions are normally based on the averaged shear-wave velocity of the top 30 m earth surface (V s30 ) (Borcherdt 1994;Hartzell et al. 2001;Wills and Clahan 2006;Wald and Allen 2007;Yong et al. 2008;Castellaro and Mulargia 2009). Wills and Silva (1998) have suggested the use of shear wave velocity for seismic site characterisation (Anbazhagan 2013). The V s30 based seismic site characterisation maps have been effectively used by the United States of Geological Survey (USGS) in developing ground shaking maps, estimating seismic loss in near real time (Earle et al. 2008) and defining generalised seismic site categories by the National Earthquake Hazard Reduction Program (NEHRP) (table 5) (Wills et al. 2000). ...
The seismic provisions for the Building Code of Pakistan were revised after the 2005 Kashmir earthquake and these have resulted in the introduction of a macrozonation ground motion hazard map in the seismic provisions. The macrozonation map proposes a peak ground acceleration (PGA) for the return period of 475 yr for Pakistan for flat rock sites. After the macrozonation, the next step is to develop the surface ground motion assessment studies for the cities, districts and tehsils of Pakistan. In this study, the
probabilistic seismic hazard analysis (PSHA) approach is used for the Peshawar District. The PSHA, consistent with the classical Cornell approach, is carried out to obtain the seismic hazard curves and uniform hazard spectra of PGA values for the return periods of 150, 475, 975 and 2475 yr at a grid spacing of 0.1◦ × 0.1◦. The PGA for Peshawar at 150, 475, 975 and 2475 yr return period is estimated as 0.23, 0.34, 0.39 and 0.45g, respectively, for rock flat outcrop site conditions. The surface ground motion maps proposed in this study incorporate the local soil effects using amplification factors based on shear wave
velocity obtained as a proxy to the topographic slope. The resultant ground surface hazard assessment proposes the PGA value of 0.63g for the return period of 475 yr and 0.89g for the return period of 2475 yr. The maps developed in the current study are important inputs for the structural designing, risk assessment and land use planning of the Peshawar District.
... Procedures and borehole datasets are described by Gibbs et al. (1980Gibbs et al. ( , 1996, Fumal et al. (1981Fumal et al. ( , 1982aFumal et al. ( ,b, 1984, Nigbor (1998), andBardet et al. (1998) (http://geoinfo.usc. edurosrine/), and Wills and Silva (1998). ...
Implications of theoretical, anelastic, seismic wave-field models for site-response estimates used in building code-provisions and in the design of critical facilities
... So, the V s results of different methods should be identical at the same site to prepare a V s 30 map using these V s 30 results. Several researchers stated that there is a good relationship between the V s 30 and geological units (e.g., Wills and Silva 1998;Holzer et al. 2005). Therefore, the relationship between the V s 30 and Holocene soil thickness is used in the present study to uniform the V s 30 results and to predict the V s 30 from the Holocene soil thickness (Fig. 12). ...
Dhaka, the capital city of Bangladesh, is one of the seismically vulnerable cities in the world due to its location close to the convergent boundary between the Eurasian and Indian Plates, unplanned urbanization, non-engineered construction practice, high population density, and weak emergency response system. The city is developed on an elevated Pleistocene terrace with surrounding Holocene floodplains. The terrace consists of the Pleistocene clayey soils, and the floodplains are composed of alluvial sandy and clayey soils. The average shear wave velocity of the near-surface soils up to a depth of 30 m (V s³⁰) is required for Dhaka City to estimate the amplification factors of seismic waves for site-specific seismic hazard analysis. Therefore, the V s³⁰ has been estimated in the city using downhole seismic (DS), multichannel analysis of surface waves (MASW), and small-scale microtremor measurement (SSMM) methods, and empirical correlation between the shear wave velocity (Vs) and standard penetration test blow count (SPT-N). The V s³⁰ has also been predicted using the relationship between the V s³⁰ and Holocene soil thickness. The V s³⁰ results of the DS, MASW, SSMM, and SPT-N vary from 127 to 320 m/s. The V s³⁰ values that are predicted based on the Holocene soil thickness vary from 145 to 260 m/s. Then, a V s³⁰ map has been prepared for Dhaka City using the V s³⁰ values that are predicted from the Holocene soil thickness at a grid of 30 m. The near-surface soils of the city are classified based on the V s³⁰ as site classes D (stiff soils) and E (soft soils) according to the NEHRP (National Earthquake Hazards Reduction Program, the USA) and as subsoil classes C and D according to the Eurocode 8.
... These stations are identified by appending their names in Table 3 with double asterisks. The V S30 values for the remaining sites are assigned approximately from surface geological descriptions (Wills and Silva 1998). Lacking more accurate values based on site-specific investigations, the V S30 values given in Table 3 can be considered reasonably good for practical engineering applications. ...
This paper presents the first uniformly processed comprehensive database on strong motion acceleration records for the extensive regions of western Himalaya, northeast India, and the alluvial plains juxtaposing the Himalaya. This includes 146 three components of old analog records corrected for the instrument response and baseline distortions and 471 three components of recent digital records corrected for baseline errors. The paper first provides a background of the evolution of strong motion data in India and the seismotectonics of the areas of recording, then describes the details of the recording stations and the contributing earthquakes, which is finally followed by the methodology used to obtain baseline corrected data in a uniform and consistent manner. Two different schemes in common use for baseline correction are based on the application of the Ormsby filter without zero pads (Trifunac 1971) and that on the Butterworth filter with zero pads at the start as well as at the end (Converse and Brady 1992). To integrate the advantages of both the schemes, Ormsby filter with zero pads at the start only is used in the present study. A large number of typical example results are presented to illustrate that the methodology adopted is able to provide realistic velocity and displacement records with much smaller number of zero pads. The present strong motion database of corrected acceleration records will be useful for analyzing the ground motion characteristics of engineering importance, developing prediction equations for various strong motion parameters, and calibrating the seismological source model approach for ground motion simulation for seismically active and risk prone areas of India.
... Then, the geologic unit designation and shear-wave velocity characteristics are applied to sites without shear-wave velocity data. This revised geologic designation improves the previous geology-based V s30 method by Wills et al. (2000) and Wills and Silva (1998). In addition, geology-topography hybrid (Scasserra et al., 2009) and geomorphometry-based proxy relationships (Yong et al., 2012) have been proposed for estimating V s30 . ...
... These amplifications were seen mostly in the north-western part of Jabalpur having 30 to 50m of thick alluvial deposits. With similar objective, numerous researchers attempted site specific response studies worldwide [13,14,15]. Any site response study requires two important inputs namely; regional ground motion records and dynamic properties of soil. ...
Effects of earthquakes (EQs) are not limited only to the epicentral region. Depending on the magnitude of the EQ and the frequency content of input motion, the damages can be widespread. The amplitude, duration and frequency content of input motion at a site further changes due to the presence of in-situ soil at the site. Thus, similar to the determination of regional seismic hazard, quantification of local site effect is equally important. Dynamic soil properties which determine the behavior of local soil under EQ loading are not readily available on regional level. Hence, standard dynamic soil properties curves developed for other regions are used for a large number of studies. In the present work, response of two soil columns consisting of clay and sand alone throughout the depth, are analyzed using equivalent linear method using 30 worldwide recorded ground motions. Based on the present analysis, two important conclusions are drawn. It is well established fact that in equivalent linear analysis, the response of soil is governed by one value of strain. First conclusion suggests that understanding equivalent linear response of same soil collectively during various recorded ground motions covering a wide range of ground motion parameters, complete nonlinear soil behavior can be understood. In such case each ground motion will provide dynamic soil properties corresponding to specific level of strain. As a second conclusion, it is found that this strain developed in the soil during each ground motion is a function of peak horizontal acceleration (PHA) of input motion as well as the thickness of overburden. Further, this strain governs the soil behavior during that particular ground motion. Thus, if this value of strain is known, the response of the soil can be determined based on one value of shear modulus and damping ratio avoiding iterative procedure. Based on the above analyses, two empirical correlations are proposed in this work, correlating above value of strain in a soil layer with the PHA of input ground motion as well as overburden thickness above the soil layer. Overburden thickness is used in place of overburden pressure since it is used in available ground response models while determining the value of strains. Knowing the PHA from seismic hazard study and overburden thickness from soil investigation, one value of strain can be estimated based on proposed correlation. The behavior of soil will be governed by this value of strain alone and thus considering complete nonlinear soil behavior may not be needed. It has to be highlighted here that the present work uses two hypothetical soil columns of sand and clay respectively to provide a general idea about the above two conclusions. For case specific correlations however, similar works can be attempted in the future.
... Information about surface geology has often been used to interpret the observed local increment of ground shaking, and several investigators have proposed empirical correlations between surface geology and local amplification (Wills and Silva 1998). The use of surface geology for characterizing the local amplification is practical and applicable to many areas because of the wide availability of geological maps, but the surface characteristics often fail to mimic the actual characteristics of the sedimentary cover. ...
The expected soil amplification has been computed for eastern Cuba considering two combined methods: a geological approach, based on the soil classification (actually two alternative methods: from surficial geology and deep lithology), and a geotechnical method, based on 1D modelling. Based on the regional geological maps, soil category maps and regional geological profiles, 45 geological models (26 for rock and 19 for surficial deposits) have been established for the entire study region. Adding the information from deep borehole data, 36 geotechnical models have been identified to represent the 19 surficial deposits in the study region, plus one for rock. In fact, after a preliminary soil characterization based only on surficial geology, the mechanical properties and thickness of the different layers within the first 30 m have been considered as main geological characteristics to identify the soil class and the related VS30, according to the NEHRP provisions, and the related proper amplification factors (AFs) have been derived. In addition, 1D soil modelling has been performed to obtain soil AFs in the homogeneous sectors in which the study region has been partitioned. A comparison performed between the AFs calculated by modelling and those estimated in agreement with the NEHRP provisions has shown quite large differences. These results, although not representing a substitution for a real microzonation study, can be useful in improving seismic hazard estimates for a general seismic risk quantification, urban planning, and seismic code updating.
... Thus, similar to the dynamic soil properties, ground motions recorded in other parts of the world are frequently used in the absence of regional ground motion records for site response analysis. In spite of the challenges mentioned above, local site effects were estimated worldwide with suitable assumptions in dynamic soil properties and bedrock motions (Philip and Aki 1986;Wills and Silva 1998;Semblat et al. 2000;Slob et al. 2002;Stewart et al. 2003;Topal et al. 2003;Pitilakis 2004;Anbazhagan and Sitharam 2008). Anbazhagan et al. (2011) performed site response analyses of typical sites at Dehradun, Lalru and Najibabad located in Uttarakhand, India using synthetic ground motions in the absence of regional ground motion records. ...
Catastrophic damages reported during an earthquake include building damages, excessive ground shaking, uneven settlements and liquefaction. While most of the seismic hazard studies map the probable level of ground shaking at the bedrock level, their use in assessing the above damages is very limited until the response of the local soil is also taken into account. Determination of the local soil response needs regionally recorded ground motions, dynamic soil properties, in situ geotechnical details, etc., which most of the time are not readily available for the region under study. In the present work, the response of local soil for Nepal has been studied indirectly taking into account the surface level of ground shaking during various past as well as recent EQs observed at various locations. Based on the present analysis, a low value of amplification factor for high peak horizontal acceleration and vice versa is observed in central, western as well as southern parts of Nepal. These observations suggest nonlinear soil behavior and are in accordance with the available literature. Further, the ground motion records during 2015 Nepal EQ show maximum soil response at 0.3 s which is exactly matching with the site class C obtained from in situ data for the above locations. Based on the above observations, various correlations between the high peak horizontal acceleration and the surface spectral acceleration are proposed to obtained site specific surface response spectrum for Nepal.
... Procedures and borehole datasets are described by Gibbs et al. (1980Gibbs et al. ( , 1996, Fumal et al. (1981Fumal et al. ( , 1982aFumal et al. ( ,b, 1984, Nigbor (1998), and Bardet et al. (1998) (http://geoinfo.usc. edurosrine/), and Wills and Silva (1998). ...
... However, the paucity of moderate or large earthquakes in Australia and, consequently, the lack of waveform records for detailed analysis of site amplification factors (AFs), makes V S30 the only parameter available for the estimation of ground-motion amplification for use in (1) Aus-tralian Building Codes (e.g., Australian Earthquake Loading Code, AS1170.4, National Earthquake Hazards Reduction Program [NEHRP] provisions) and (2) design applications by the earthquake engineering community (Boore et al., 1997;Wills and Silva, 1998;Dobry et al., 2000;Boore, 2004b). Consequently, establishing the best practices of V S30 estimation is paramount for Australian settings. ...
Although the time-averaged shear-wave velocity down to 30 m depth (V-S30) can be a proxy for estimating earthquake ground-motion amplification, significant controversy exists about its limitations when used as a single parameter for the prediction of amplification. To examine this question in absence of relevant strong-motion records, we use a range of different methods to measure the shear-wave velocity profiles and the resulting theoretical site amplification factors (AFs) for 30 sites in the Newcastle area, Australia, in a series of blind comparison studies. The multimethod approach used here combines past seismic cone penetrometer and spectral analysis of surface-wave data, with newly acquired horizontal-to-vertical spectral ratio, passive-source surface-wave spatial autocorrelation (SPAC), refraction microtremor (ReMi), and multichannel analysis of surface-wave data. The various measurement techniques predicted a range of different AFs. The SPAC and ReMi techniques have the smallest overall deviation from the median AF for the majority of sites. We show that V-S30 can be related to spectral response above a period T of 0.5 s but not necessarily with the maximum amplification according to the modeling done based on the measured shear-wave velocity profiles. Both V-S30 and AF values are influenced by the velocity ratio between bedrock and overlying sediments and the presence of surficial thin low-velocity layers (< 2 m thick and < 150 m/s), but the velocity ratio is what mostly affects the AF. At 0.2 < T < 0.4 s, the AFs are largely controlled by the surficial geology of a particular site. AF maxima are the highest in the hard classes, which is the inverse of the findings used in the Australian Building Code. Only for T > 0.5 s do the amplification curves consistently show higher values for soft site classes and lower for hard classes.
... So, the V s results of different methods should be identical at the same site to prepare a V s 30 map using these V s 30 results. Several researchers stated that there is a good relationship between the V s 30 and geological units (e.g., Wills and Silva 1998;Holzer et al. 2005). Therefore, the relationship between the V s 30 and Holocene soil thickness is used in the present study to uniform the V s 30 results and to predict the V s 30 from the Holocene soil thickness (Fig. 12). ...
Average shear wave velocities of the subsurface geological materials of Dhaka City up to a depth of 30 m (AVS30) have been estimated using in-situ site investigation techniques such as, Downhole Seismic, Multichannel Analysis of Surface Wave (MASW), Small Scale Microtremor Measurement (SSMM) and Standard Penetration Test (SPT) blow counts (N-values). Then shear wave velocity map of the city is prepared using AVS30 of different locations. The AVS30 of the subsurface geological materials of the city varies from 127 m/sec to 295 m/sec. The central part, from north to south and the middle western part of the city exhibit high shear wave velocities from 200 m/sec to 295 m/sec whereas the eastern and western parts of the city show low shear wave velocities from 127 m/sec to 240 m/sec. The geological materials of the city are classified as site classes D (stiff soils) and E (soft soils) based on AVS30 according to NEHRP (National Earthquake Hazards Reduction Program, USA). The AVS30 map is generally used to determine the amplification factors for site-specific seismic hazard analysis.
... The absolute band composite method (Kahle and Rowan 1980) was utilized to identify the surface GG of each terrain unit previously identified. Then, the spatial distribution of the discriminated surface lithology was correlated with the preassigned terrain units to allocate ranges of shearwave velocity (Wills and Silva 1998). The physical properties of the rock are one of the most important factors that control the seismic velocity (i.e. ...
The identification of natural hazard prone areas for future planning requires an efficient decision support tool to provide the appropriate weights for the various topographical, geological, and seismological factors responsible for the expected hazards. In the present study, an analytical hierarchy process (AHP) with six earthquake hazard parameters (EHPs) was used as a decision support system for the identification of earthquake triggered hazards in the Al-Madinah region of the Kingdom of Saudi Arabia. The pairwise comparison matrix and the final weights for all the EHPs during the implementation of AHP were calculated with an acceptable limit of consistency ratio. A GIS-based integrated analysis was carried out on all the selected attributes to generate the final hazard and microzonation map. From the analysis, it was observed that 15 % of the region fall under a very high or high hazard category. The very high seismic hazard zone is located in the northwestern region of Al-Madinah province, while the eastern and southern regions show low to very low hazard. The result of the study may be used as a first-level hazard and reliability map in selecting the appropriate earthquake resistant sites in designing the forthcoming new buildings against the potential seismic hazard of the province.
... El mapa geológico del Cuaternario del Valle de Caracas (Figura 2), producido por Singer et al. (2007) a tal efecto, refleja la complejidad de las condiciones geológicas de esta depresión aluvial de origen neotectónico, las cuales son susceptibles de modificar el comportamiento de las ondas sísmicas, de acuerdo a la respuesta dinámica de los diversos cuerpos de sedimentos que éstas atraviesan. Los fundamentos metodológicos de la pertinencia de una base de información detallada de geología del Cuaternario como la producida para el conjunto del Valle de Caracas, para fines de microzonificación sísmica, se basa en los resultados experimentales cada vez más numerosos y promisores obtenidos en diversas regiones del planeta como Japón, Taiwán, Australia, Italia, y en particular en California, concernientes a la existencia de correlaciones empíricas representativas para fines de predicción de valores de velocidad de ondas de corte Vs30, entre el desglose cartográfico de unidades geológicas aluviales cuaternarias definidas entre otros criterios, a partir de parámetros estratigráficos de edad relativa y por medio de geología de superficie, y la correspondiente categorización de las respuestas sísmicas de los suelos en diversos niveles escalares de resolución (Park & Elrick, 1998;Wills & Silva, 1998;Wills et al., 2000;Wills & Clahan, 2006). Figura 1. Ubicación del área de estudio (Garrity et al., 2004). ...
Due to the lack of subsoil geological information of the alluvial sediments, has been created a urban geology database for the Caracas Valley. These geological data base supports a geological proposal of 11 microzones considered homogeneous for seismic microzoning, which have been reflected on a quaternary map of geological formations and faults. The characterization of each microzone is based on the geological evaluation of 7 parameters considered as significant.
... In areas of low seismicity and a lack of strong ground motion records, one way to classify the seismic site effect distribution is by means of the correlations between surface geology, borehole data (lithologic) and shear-wave velocity measurements. This approach was used in several areas (e.g., Tinsley and Fumal, 1985;Park and Elrick, 1998;Rodríguez-Marek et al., 2001;Stewart et al., 2003) to generate local and regional maps (Wills and Silva, 1998;Wills et al., 2000) according to site categories of the National Earthquake Hazards Reduction Program (NEHRP) and to predict amplification factors which are included in attenuation relations. ...
A first microzonation map of seismic site class distribution in Monterrey Metropolitan area is presented. This was prepared using borehole information, seismic refraction profiling and surficial geology. According to geotechnical site categories proposed by Rodriguez-Marek et al. (2001) and NEHRP soil classification (VS30), C, C1-C2 sites classes are located to the south and central of the study area. In the northwest zone, B site classes are dominant. Lowest S-wave velocity (average of 268 m/s) correspond to silts, whereas highest velocities (average 2311 m/s) are related to Cretaceous limestones. Maximum thicknesses (16 to 20 m) of the soft sediments C-C2 classes are located at the center area being correlated to two paleo-channels. This study provides an initial attempt to understand and characterize the seismic site classes in the study area.
... The time-averaged shear-wave velocity to a depth of 30 m (Vs30) is used extensively in building design codes (e.g., International Code Council, 2006), earthquake-engineering applications (Borcherdt, 1994;Kramer, 1996;Boore et al., 1997;Wills and Silva, 1998;Dobry et al., 2000), and ground-motion prediction-equation relationships (Zhao and Xu, 2013). Proxies for Vs30, including surface geology-, slope-, and terrain-based methods have been developed to predict Vs30 where direct measurements are sparse (Wills et al., 2000;Wald and Allen, 2007;Yong et al., 2012). ...
We characterize shear-wave velocity versus depth (Vs profi le) at 16 portable seismograph sites through the epicentral region of the 2011 Mw 5.8 Mineral (Virginia, USA) earthquake to investigate ground-motion site effects in the area. We used a multimethod acquisition and analysis approach, where active-source horizontal shear (SH) wave reflection and refraction as well as active-source multichannel analysis of surface waves (MASW) and passive-source refraction microtremor (ReMi) Rayleigh wave dispersion were interpreted separately. The time-averaged shear-wave velocity to a depth of 30 m (Vs30), interpreted bedrock depth, and site resonant frequency were estimated from the best-fi t Vs profi le of each method at each location for analysis. Using the median Vs30 value (270-715 m/s) as representative of a given site, we estimate that all 16 sites are National Earthquake Hazards Reduction Program (NEHRP) site class C or D. Based on a comparison of simplifi ed mapped surface geology to median Vs30 at our sites, we do not see clear evidence for using surface geologic units as a proxy for Vs30 in the epicentral region, although this may primarily be because the units are similar in age (Paleozoic) and may have similar bulk seismic properties. We compare resonant frequencies calculated from ambient noise horizontal:vertical spectral ratios (HVSR) at available sites to predicted site frequencies (generally between 1.9 and 7.6 Hz) derived from the median bedrock depth andaverage Vs to bedrock. Robust linear regression of HVSR to both site frequency and Vs30 demonstrate moderate correlation to each, and thus both appear to be generallyrepresentative of site response in this region. Based on Kendall tau rank correlation testing, we fi nd that Vs30 and the site frequency calculated from average Vs to median interpreted bedrock depth can both be considered reliable predictors of weak-motion site effects in the epicentral region.
... Proper estimation of induced effects depends upon the accuracy in the site response analysis. Many researchers have attempted to estimate the local site effects in India and worldwide (Philips and Aki 1986;Wills and Silva 1998;Semblat et al. 2000;Slob et al. 2002;Stewart et al. 2003;Topal et al. 2003;Pitilakis 2004;Anbazhagan and Sitharam 2008). However, most of the earlier site response studies were region specific where a broad picture of ground motion amplification, predominant period and period of highest spectral accelerations were estimated. ...
Destructive moderate to major earthquakes across the globe have highlighted various possible forms and extent of damages. Subsoil properties play a vital role in controlling the actual damage scenario. Induced effects such as liquefaction and landslide are also the functions of surface ground shaking. In the present work, site response analyses based on equivalent linear model using SHAKE2000 are attempted to assess the surface scenario. In the absence of recorded data at the site under consideration, globally recorded ground motions from Pacific Earthquake Engineering Research database are considered. Site response analyses results show variation in amplification factor as high as 7.4. Post-filtering of the analyses results has been proposed in this work considering the site condition as well as the design requirements. Based on the filtering, the above value of amplification factor has been reduced to 2.5. This reduction will considerably affect the design values and subsequently the construction cost. In addition, the value of surface peak ground acceleration proposed in this work matches closely with the earlier published literature as well as the codal provisions.
... Higher intensity zones correspond mainly to surface deposits of sand and clay and are located primarily along the south-east shore, the south central section, and several areas in the south-west section of the island. Preliminary seismic microzonation maps can also be derived by correlating geological units and/or surface geology to regional data on V s30 (Ansal et al. 2010;Holzer et al. 2005;Wills and Clahan 2006;Wills et al. 2000;Wills and Silva 1998). Typically, a representative shear-wave velocity is determined from shear wave velocity profiles for each geologic unit (Holzer et al. 2005;Wills et al. 2000). ...
In most national building codes, site classification is based on the Vs30 parameter, the average shear wave velocity for the first 30 m of soil below the surface, and defines amplification factors (e.g. Fa and Fv) to be applied to ground motions for a reference condition. Seismic microzonation mapping is usually achieved by combining information from various sources, each with varying degrees of uncertainties. A preliminary microzonation can be derived from surface geology or surface elevation maps, while a more detailed and accurate map is usually based on extensive seismic surveys. A procedure is proposed that progressively allows the integration of information from various sources and to estimate the degree of uncertainty on the microzonation. This allows planners to determine where microzonation maps require further investigations given current or future urban development plans. The proposed procedure uses conditional second moment estimation and provides the best linear unbiased estimates of Vs30 and its uncertainty. Next, these estimates are used to derive soil classification probability maps and to compute the expected values and variance of soil amplification factors Fa ad Fv to be used in probabilistic seismic risk analyses. The proposed procedure is demonstrated for the seismic microzonation of the island of Montreal.
... Classified terrane units are therefore assigned V s30 to generate a seismic site characterization map (Fig. 4). The values applied are based on results from Yong et al. (2008) who derived V s30 values from geology (Wills and Silva, 1998) and spatially correlated the values with terrane units such as mountains, pied-monts and basins. For mountains, Yong et al. (2008) proposed V s30 values of >500 m s )1 , for piedmonts V s30 values between 200 and 600 m s )1 and for basins V s30 values of <300 m s )1 (Fig. 4). ...
Preparing seismic site characterization maps requires extensive geological and geotechnical data collection and interpretation. This study evaluates a remote sensing-based method to generate seismic site characterization map at 30-m spatial resolution. Geographical object-based image analysis was applied to topographic attributes computed from an Advance Spaceborne Thermal Emission and Reflection Radiometer Digital Elevation Model to demarcate terrane units of mountains, piedmonts and basins. Classified terrane units were verified through a field-based landform map resulting in an accuracy of 70%. To evaluate the importance of classified terrane units for seismic site characterization and their role in earthquake-induced building damage, the classified terrane units were compared with 2005 Kashmir earthquake damage data derived from field visits and SPOT-5 imagery. This shows that 81% of the less, moderate and severe damage intensity zones correspond with mountains, piedmonts and basins respectively. Classified terrane units were assigned Vs30 to generate a seismic site characterization map.
... Although this more refined geological classification has generally not been used, Campbell and Bozorgnia (2000) empirically demonstrate the importance of this more refined classification scheme in the estimation of near-source ground motion. Park and Elrick (1998) and Wills and Silva (1998) have also shown that a more refined geological classification might be warranted based on measurements of shear-wave velocity for different geologic units in California. ...
... The time-averaged shear-wave velocity to a depth of 30 m (Vs30) is used extensively in building design codes (e.g., International Code Council, 2006), earthquake-engineering applications (Borcherdt, 1994;Kramer, 1996;Boore et al., 1997;Wills and Silva, 1998;Dobry et al., 2000), and ground-motion prediction-equation relationships (Zhao and Xu, 2013). Proxies for Vs30, including surface geology-, slope-, and terrain-based methods have been developed to predict Vs30 where direct measurements are sparse (Wills et al., 2000;Wald and Allen, 2007;Yong et al., 2012). ...
... Le nombre de puits à partir duquel la structure géotechnique a été modélisée est plus de 180 avec des profondeurs variant de 20 à 120m. En se basant sur les informations et 7ème Colloque National AFPS 2007 -Ecole Centrale Paris 3 données de forages ainsi que sur la littérature existante, la stratification géotechnique a été établie [Tokimatsu, 1997] [Su et al., 1995], [Mancuso et al, 1997], [Pitilakis et al., 1992] [Wills et al., 1998]. Afin d'analyser de la réponse du site d'étude et l'estimation de l'amplification, un modèle de sol avec tous les paramètres géotechniques et dynamiques ainsi que leur variation en profondeur et en plan est requis [Kramer, 1997]. ...
en surface est significativement affectée par l'effet combiné de la rigidité dynamique et l'épaisseur des dépôts superficiels. Le règlement parasismique Algérien (RPA99-2003), distingue quatre catégories de sites. Ils sont établis à partir des données géotechniques moyennes et spécialement la vitesse d'onde de cisaillement sur les 20 premiers mètres. Pour certains de site tels que les dépôts épais, cette vitesse ne traduit pas réellement ses conditions dynamiques. Pour étudier l'effet de l'épaisseur sur la classe du site, différents modèles sont considérés. Il s'agit de comparer leurs fréquences fondamentales et l'accélération maximale en surface libre. Le programme SHAKE est utilisé, L'événement de Keddara enregistrée lors du séisme de Boumerdes 2003 (ML=6.8) est pris comme excitation à la base. Les résultats de cette étude ont montré d'une part que la vitesse moyenne ne suffit pas pour caractériser un site. D'autre part, l'épaisseur de référence dans le RPA99-2003 permet de classer les sites fermes et ne traduit pas les conditions réelles des sites meubles à très meuble. Une épaisseur de référence plus importante est conseillée. ABSTRACT. Seismic site response and amplification of ground motion are significantly affected by the combined effect of the dynamic stiffness of the soil and the thickness the deposit. In Algerian design practice (RPA99-2003), four site types are considered; they are established from properly substantiated geotechnical data especially average shear wave velocity over the upper 20 meters of a site profile. The study is based on the average S-wave velocity of four soil profiles with different thicknesses. For each model, we calculate its fundamental frequency and acceleration at free surface. A one-dimensional wave propagation analysis was performed using the equivalent-linear program SHAKE2000, the Keddara event recorded during the Boumerdes earthquake (ML=6.8) is used as input motion. The results show first significant differences in average s-wave velocities which affect the site classification. The average S wave velocity is not sufficient to characterise the site. The thickness of 20m makes good classification of stiff soils but does not represent soft to very soft soils. We recommend using a reference thickness higher than 20m. MOTS-CLÉS : Vitesse d'onde cisaillement, profil, sol, épaisseur, fréquence, amplification, RPA99-2003
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.
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.
Although Egypt has not been subjected to high seismic hazards, it does face a very high level of risk on this front. Even a small earthquake of moderate magnitude, such as the Faiyum earthquake of 1992 (Ms = 5.2), may turn into a catastrophic event causing collapse of or irreparable damage to thousands of buildings. This vulnerability is due to the country’s lack of seismic site classifications and bad engineering conditions of buildings, especially in villages. A total of 71 drilling boreholes and about 82 shear wave seismic velocity tests varying between the Downhole, Crosshole, Refraction Microtremors (ReMi), and Multichannel Analysis Surface Waves (MASW) methods were used to prepare the microseismic zonation maps for Egypt. Microseismic zonation maps were introduced using the geological map of Egypt, NEHRP Seismic site classifications based on “shear wave velocity” (Vs 30), and the “soil refusal depth map” (SPT (N30) = 50). Furthermore, new empirical equations to obtain Vs 30 versus SPT (N30) were introduced to help engineers and seismologists obtain the desired dynamic properties of the soil, such as the dynamic shear modulus (G). The seismic activities inside the Egyptian plate were combined with the microseismic zonation maps to analyze the important seismic hazards; this was done for variable soils. The present study is expected to be a regional reference for the expected shear wave velocity, SPT (N30) value, and shear rigidity constant for the different Egyptian soils and to help in the developing projects.
Site amplification coefficients and acceleration design response spectra (ADRS) for the deep Indo-Gangetic Basin (IGB) have been proposed. Non-linear site response analysis is carried out at 275 deep shear wave velocity (V S) profiles by selecting the input motion based on seismic hazard map for 10% probability of exceedence in 50 years. The spatial variation map of peak ground acceleration (PGA) and spectral acceleration (SA) at surface and various depths for the IGB are also presented. The bedrock PGA of 0.03-0.24 g increased to 0.1-0.97 g at surface and 0.05-0.35 g at a depth of 150 m. Maximum SA is observed between 0.08 s and 0.5 sec. The new site factors viz. F a and F v are derived for newly defined spectral period range. Further, ADRS is constructed which depends on PGA and seismic site class as per NEHRP. Proposed ADRS is compared with different deep basin studies and BIS:1893.
This chapter predominantly discuss about the role of Local site conditions on the amplification of seismic waves and the resulted earthquake disasters. In-depth discussions are made on the various local site conditions which influence the ground shaking. Different available methods for the assessing the local site conditions are presented in this chapter. Various codal provisions for site classifications are also discussed here. This chapter also presents the assessment of local site effect at micro and macro-level using the appropriate methodologies.
Multichannel Analysis of Surface Wave (MASW) is one of the latest geophysical methods used for determining the shear wave velocity of the soil. A series of MASW tests were carried out in this study using a multi channel seismograph with 24 numbers of 4.5 Hz vertical geophones. Collected data were analysed using Surface Plus software. One-dimensional shear wave velocity models were developed from the analyses of the collected data for the Jaipur city. The average shear wave velocity (VS30) for the top 30 m of soil deposit was estimated for the Jaipur city. Based on this VS30 value, the Jaipur city was finally divided into various sub-zones as per the NEHRP guidelines. From the study it has been observed that all the studied areas are falling either in site class C or D. In top 15 m depth, almost all studied area is having average shear wave velocity less than 360 m/s. The estimated shear wave velocity data were used in the assessment of liquefaction potential of soil at various locations in the city. From the liquefaction potential results it can be concluded that most of the city area is not susceptible to liquefaction.
The contribution of remote sensing and geographical information system (GIS) techniques to estimate the surface level seismic hazard was investigated using topographic gradient maps in the states of Tripura and Mizoram. This paper addresses a vital issue on the estimation of the seismic hazards of Northeast (NE) India, where the hazards are high and the risk is also high. In developing site response maps or seismic hazard (surface acceleration) maps, it is difficult to obtain near-surface soil data (site-specific data) through geophysical/geotechnical field investigations at a smaller resolution scale (a state/region or country level). The topographic slope provides a reliable proxy because the rocky materials maintain a steep gradient/slope compared to soft soil deposits. In this paper, peak ground acceleration (PGA) at the bedrock for the states of Tripura and Mizoram in NE India has been estimated using probabilistic seismic hazard analysis (PSHA), which considers linear sources and events (from 1731 to 2010) with appropriate ground motion prediction equations applicable for NE India. Further, the authors have adopted the square root impedance model to estimate the spectral amplification of the study area to bring the hazard from bedrock level to surface. Authors have classified the entire study area as site classes B, C, and D categories and thereafter estimated spectral amplifications for the site periods (0.40, 0.21, 0.11, and 0.01 s). The surface level PGA (g) and amplification maps have been developed using a probabilistic approach considering PGA at the bedrock level. The results indicate that this area is highly sensitive to spectral responses, such as spectral acceleration or spectral amplification rather than PGA.
This paper presents the first seismic regionalization map for Nuevo Leon state, at a scale of 1:250 000. It was made using geological information and P and S wave propagation velocity data. Seismic refraction methodology was used to obtain the wave velocity propagation. A total of 708 profiles were made on different geologic units that are included in the Nuevo Leon state type-lithological column. Outcrops on which the profiles were carried out include sedimentary, igneous, and metamorphic rocks, and Quaternary deposits. The generation of the seismic site conditions map is based on site effect codes, as proposed by the National Earthquake Hazards Reduction Program (NEHRP, U.S.A.), from VS30 determination and its correlation with lithological information. The regionalization map using VS30, has revealed that A (VS30 > 1500 m/s), B (760 < VS30 ≤ 1500), and C (360 < VS30 ≤ 760) class sites predominate in the study area. Areas characterized by alluvial material show lower values of VS30 (560 m/sec), whereas consolidated rocks, for example, those that constitute the Mesozoic sequences, display high seismic wave velocity propagation values (VS30 = 1200 - 3500 m/s). The results obtained in this work provide a first approximation of the seismic response of shallow materials in the state, whose use is important in the land use planning, urban development and for the calculation of seismic risk and other geological perils, particularly for areas with historical evidence of seismic activity, but with little or no seismic instrumentation.
This study presents an overview of seismic microzonation and existing methodologies with a newly proposed methodology covering all aspects. Earlier seismic microzonation methods focused on parameters that affect the structure or foundation related problems. But seismic microzonation has generally been recognized as an important component of urban planning and disaster management. So seismic microzonation should evaluate all possible hazards due to earthquake and represent the same by spatial distribution. This paper presents a new methodology for seismic microzonation which has been generated based on location of study area and possible associated hazards. This new method consists of seven important steps with defined output for each step and these steps are linked with each other. Addressing one step and respective result may not be seismic microzonation, which is practiced widely. This paper also presents importance of geotechnical aspects in seismic microzonation and how geotechnical aspects affect the final map. For the case study, seismic hazard values at rock level are estimated considering the seismotectonic parameters of the region using deterministic and probabilistic seismic hazard analysis. Surface level hazard values are estimated considering site specific study and local site effects based on site classification/ characterization. The liquefaction hazard is estimated using standard penetration test data. These hazard parameters are integrated in Geographical Information System (GIS) using Analytic Hierarchy Process (AHP) and used to estimate hazard index. Hazard index is arrived by following a multi-criteria evaluation technique - AHP, in which each theme and features have been assigned weights and then ranked respectively according to a consensus opinion about their relative significance to the seismic hazard. The hazard values are integrated through spatial union to obtain the deterministic microzonation map and probabilistic microzonation map for a specific return period. Seismological parameters are widely used for microzonation rather than geotechnical parameters. But studies show that the hazard index values are based on site specific geotechnical parameters.
This paper presents the first seismic regionalization map for Nuevo Leon state, at a scale of 1:250 000. It was made using geological information and P and S wave propagation velocity data. Seismic refraction methodology was used to obtain the wave velocity propagation. A total of 708 profiles were made on different geologic units that are included in the Nuevo Leon state type-lithological column. Outcrops on which the profiles were carried out include sedimentary, igneous, and metamorphic rocks, and Quaternary deposits. The generation of the seismic site conditions map is based on site effect codes, as proposed by the National Earthquake Hazards Reduction Program (NEHRP, U.S.A.), from VS30 determination and its correlation with lithological information. The regionalization map using VS30, has revealed that A (VS30 > 1500 m/s), B (760 < VS30 ¿ 1500), and C (360 < VS30 ¿ 760) class sites predominate in the study area. Areas characterized by alluvial material show lower values of VS30 (560 m/sec), whereas consolidated rocks, for example, those that constitute the Mesozoic sequences, display high seismic wave velocity propagation values (VS30 = 1200 - 3500 m/s). The results obtained in this work provide a first approximation of the seismic response of shallow materials in the state, whose use is important in the land use planning, urban development and for the calculation of seismic risk and other geological perils, particularly for areas with historical evidence of seismic activity, but with little or no seismic instrumentation.
Thirty-meter shear-wave velocity (V-S30) is commonly used to estimate near-surface conditions for site classification, seismic site response, liquefaction analysis, and other geotechnical earthquake engineering application. Quantifying the uncertainty in V-S30 measurements is important for determining the accuracy and precision of this geophysical test. This study gathers existing available comparative and blind shear-wave velocity tests to evaluate the apparent or observable intra- and intermethod variability. Presented in this article are estimates of V-S30 uncertainty for the invasive methods of downhole, suspension logging, and seismic cone penetration testing, the noninvasive method of spectral analysis of surface waves, and the method of shear-wave velocity correlated geologic units. Discussed is the issue of soil disturbance with respect to invasive methods and how this may result in measurement bias. Results of this study indicate that uncertainty of shear-wave velocity measurements are on the order of 1%-3% coefficient of variation (standard deviation/mean) for downhole, suspension logging, and seismic cone penetration testing, 5%-6% coefficient of variation for spectral analysis of surface waves, and 20%-35% coefficient of variation for shear-wave velocity correlated geologic units. Presented here are procedures for propagating the uncertainty and/or bias in forward analyses.
This study was prompted by the recent availability of a significant amount of openly accessible measured VS30 values and the desire to investigate the trend of using proxy-based models to predict VS30 in the absence of measurements. Comparisons between measured and model-based values were performed. The measured data included 503 VS30 values collected from various projects for 482 seismographic station sites in California. Six proxy-based models-employing geologic mapping, topographic slope, and terrain classification-were also considered. Included was a new terrain class model based on the Yong et al. (2012) approach but recalibrated with updated measured VS30 values. Using the measured VS30 data as the metric for performance, the predictive capabilities of the six models were determined to be statistically indistinguishable. This study also found three models that tend to underpredict VS30 at lower velocities (NEHRP Site Classes D-E) and overpredict at higher velocities (Site Classes B-C).
Introduction
The increasing importance of shear wave velocity ( Vs ) in shallow subsurface materials for determining the seismic shaking characteristics of a site (Borcherdt, 1994; Anderson et al. , 1996) has led to a search for new, more efficient methods of measuring Vs . One of these new techniques, called “CXW” by Poran et al. (1994), uses surface-wave dispersion to infer the shear-wave velocity profile at a site. This technique has been used extensively in the Los Angeles Basin, and the profiles have been incorporated in the geotechnical database by Vucetic and Doroudian (1995). Examination of these profiles and comparison with profiles measured using traditional downhole and crosshole techniques shows that the profiles measured using the CXW technique are not similar to profiles measured using more established methods.
This note is a spin-off of an effort at the California Department of Conservation, Division of Mines and Geology (DMG) to develop a statewide map...