Article

Directivity in NGA Earthquake Ground Motions: Analysis Using Isochrone Theory

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Abstract

We present correction factors that may be applied to the ground motion prediction relations of Abrahamson and Silva, Boore and Atkinson, Campbell and Bozorgnia, and Chiou and Youngs (all in this volume) to model the azimuthally varying distribution of the GMRotI50 component of ground motion (commonly called "directivity") around earthquakes. Our correction factors may be used for planar or nonplanar faults having any dip or slip rake (faulting mechanism). Our correction factors predict directivity-induced variations of spectral acceleration that are roughly half of the strike-slip variations predicted by Somerville (1997), and use of our factors reduces record-to-record sigma by about 2-20% at 5 sec or greater period.

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... There have been substantial efforts over the last couple of decades to develop adjustments to empirical GMMs (also known as ground motion prediction equations (GMPEs)) to capture near-fault directivity effects. Adjustment approaches have been based on fitting empirical ground motion data to simple functional forms (e.g., Somerville et al., 1997) and/or theoretical models (e.g., isochrone theory that accounts for the radiation pattern and general behaviors expected for near-fault seismic waves; e.g., Spudich & Chiou, 2008). These directivity adjustments mostly vary with the azimuthal angle and distance of an observing site to the fault, typically predicting (for strike-slip events) amplifications distributed as a wedge centered along the fault trace, as illustrated in Figure 1. ...
... Indeed, as noted by Spudich et al. (2014), large near-rupture ground motion records such as the Lucerne record of the Landers earthquake are frequently observed within the along-strike end points of the causative rupture trace, even though current directivity amplification adjustment models generally place the amplification maximum at (or just beyond) the rupture ends. Spudich and Chiou (2008) explain this phenomenon using isochrone synthetics, which inherently includes the scaling of peak period with epicentral distance, leading to a complex pattern of peak PSV. ...
... A number of modifications to empirical GMPE have been proposed to account for rupture directivity and the strong FN pulse (e.g., Rowshandel, 2010;Somerville et al., 1997;Spudich et al., 2014;Spudich & Chiou, 2008). As an example for this process, Somerville et al. (1997) introduced (e.g., in the strike-slip case) directivity parameter (Xcosθ), with X representing the proportion of the fault rupture distance that is toward a site of interest and θ representing the effect of the radiation direction relative to the fault strike. ...
Article
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Near‐fault motion is often dominated by long‐period, pulse‐like particle velocities with fault‐normal polarization that, when enhanced by directivity, may strongly excite mid‐ to high‐rise structures. We assess the extent to which plastic yielding may affect amplitude, frequency content, and distance scaling of near‐fault directivity pulses. Dynamic simulations of 3D strike‐slip ruptures reveal significant plasticity effects, and these persist when geometrical fault roughness is added. With and without off‐fault yielding, these models (~ M 7) predict fault‐normal pulse behavior similar to that of observed pulses (periods of 2‐5 seconds, amplitudes increasing with rupture distance until approaching a limit), but yielding systematically reduces pulse amplitude and increases the dominant period. Yielding causes near‐fault (< ~2 km) peak ground velocity (PGV) to saturate with respect to increases in both stress drop and epicentral distance, and, in that distance range, yielding may contribute significantly to the observed magnitude saturation of PGV. The results support the following elements for functional forms in empirical pulse models: (i) a fault‐normal distance saturation factor, (ii) a period‐dependent and along‐strike distance‐dependent factor representing directivity, and (iii) an along‐strike saturation factor to truncate growth of the directivity factor. In addition to the foregoing effects on long‐period fault‐normal pulses, the model with off‐fault plasticity is very efficient in suppressing the high‐frequency fault‐parallel acceleration pulses that otherwise develop when rupture breaks free surface. This effect is likely to inhibit the initiation of a sustained supershear rupture triggered by a strong free surface breakage.
... Compared with far-field earthquakes, pulse-like ground motions observed in near-field regions display more complex characteristics, such as the apparent velocity pulse and permanent displacement [1][2][3]. Many structures under the action of pulse-like excitations have been found to suffer more considerable inelastic deformation and more severe damage [4]. ...
... the seismic demand of columns under the action of velocity with larger V p, particularly in the most unfavorable range of T p . (3). Finally, the proposed spectra are also applied to obtain the optimal design range of longitudinal reinforcement ratio, and the influence of T p on structural response is directly incorporated into the design state of columns in near-field regions. ...
Article
The seismic ductility spectra (SDS) method is a crucial tool to quickly evaluate the ductility demand of bridge columns with varied constitutive models. However, conventional SDS methods usually do not consider the characteristics of pulse-like excitations, which tend to cause severe structural damage. To address this challenge, near-fault pulse seismic ductility spectra (NFPSDS) based on Machine learning (ML) are developed in this study, where two ML models, i.e., the Random Forest (RF) and the artificial neural network (ANN), are utilized to map the relationship between seismic demand and a pulse-structure coupled index α 1-p (the structural fundamental period (T 1) relative to pulse period (T p)). Then, the influence of column parameters (such as fundamental period and longitudinal reinforcement ratio) and pulse parameters (such as pulse period and peak pulse velocity) on NFPSDS is quantitatively investigated. Thus, by employing the NFPSDS method, the reasonable design range of longitudinal reinforcement ratio can be obtained under different pulse periods and pulse velocities. Overall, the NFPSDS method significantly benefits the practice for seismic design of structures in near-fault regions.
... The characteristics of the FN component are also reflected in acceleration and velocity response spectra, where there is a shift in peak spectral amplitude as a function of magnitude towards a higher time period [16]. In a strike-slip fault, based on the polarization of seismic waves, a directivity pulse is perceived in the FN component at stations located in the direction of rupture [17,18]. In contrast, fling action [19] persists in the Fault Parallel (FP) components at stations located perpendicular to the direction of rupture. ...
... Fig. 5 shows a bar chart of the Isochrone Directivity Parameter (IDP) parameter, a measure of directivity content at a station. IDP is computed using directivity parameters [18]. The IDP parameter typically depends on two factors, the fraction of the fault (s) lying between the epicenter and station and 'c', which addresses the azimuth of the station with respect to the epicenter and fault trace. ...
Article
The variability in source characteristics induces spatial variability in the characteristics of near-field ground motion intensities which in turn impacts the fragility behaviour of structures. The study aims to quantify such variability in fragility curves of low-rise structures with a natural period of 0.2 sec with change in nucleation asperity, a source parameter of earthquake rupture corresponding to (Mw ⋍ 7). Four rupture scenarios are considered which differ from each other based on the position of nucleation asperity. The rupture scenarios are termed as bilateral, partial bilateral, partial unilateral, and unilateral, respectively. For bilateral rupture, the nucleation asperity is placed exactly in the middle of the fault face. In contrast, in the unilateral case, the nucleation asperity is placed at the end of the fault. Additionally, fragility curves corresponding to each horizontal component (fault-parallel and fault-normal) of ground motions at stations with varying rupture distances are also highlighted. The study is also extended to evaluate structures’ fragility behaviour with a natural period of 0.6 sec, 1 sec and 4 sec. Additionally bi-directional response to the simulated ground motions were emphasized.
... The Isochrone Directivity Parameter (IDP) given by Spudich and Chiou (2008) [80] is based on the projected point from the station onto the fault plane. In 2013, the same authors formulated Direct Point Parameter (DPP) with respect to the "direct point" expressed in terms of a different isochrone velocity ratio ĉ' [27] (CS2013). ...
... The Isochrone Directivity Parameter (IDP) given by Spudich and Chiou (2008) [80] is based on the projected point from the station onto the fault plane. In 2013, the same authors formulated Direct Point Parameter (DPP) with respect to the "direct point" expressed in terms of a different isochrone velocity ratio ĉ' [27] (CS2013). ...
Article
Directivity is a phenomenon perceived during fault ruptures wherein the ground motion and spectral response in the direction of the rupture is more significant than in any other direction. The objective of this study is to evaluate the variability in characteristics of near-fault ground motions as well as the ductility demand on structures due to directivity based on simulations of strike-slip earthquake events by employing SPECFEM3D, a physics-based ground motion simulation code. To understand the finite fault propagation effect, a source effect, the vertical strike-slip fault is considered to be embedded in an elastic half-space, to prevent the influence of path and site effects. Two scenarios are designed based on the positioning of nucleation asperity (NA): (1) in the middle of the fault face to simulate bilateral (BL) rupture and (2) shifted to one end for the case of unilateral (UL) rupture. The ground motions at near-fault stations, located in a racetrack configuration around the surface trace of the fault, are analyzed. In addition to a high spectral content in the forward directivity stations as a result of UL rupture, directivity velocity pulses identified in the fault-normal components are higher than the fling step velocity pulses in the fault-parallel component for the racetrack stations considered. Furthermore, the study examines the correlation between ductility demands computed based on elastoplastic rheology with direct point parameter and ground motion intensity measures for directivity and fling step stations.
... According to Spudich et al. (2014), in the initial NGA-West project, directivity was not included as an explicit term in the GMPEs that were developed. Instead, directivity functions were developed (e.g., Spudich and Chiou, 2008;Rowshandel, 2010) as post hoc "corrections" to the median of an NGA GMPE by fitting directivity functional forms to the residuals of that GMPE. However, applying these directivity corrections in practice is challenging. ...
... NGA-West or interim GMPEs. It is generally considered that the directivity is stronger when the distance the rupture travels is longer (e.g., Somerville et al., 1997;Schmedes and Archuleta, 2008;Spudich and Chiou, 2008;Spudich et al., 2014;Zhang et al., 2017). Without a full understanding of this phenomenon for heterogeneous rupture, all the five directivity models summarized in Spudich et al. (2014) have chosen the conservative approach of forbidding directivity amplification to decay with distance from the hypocenter along the fault trace. ...
Article
Full-text available
The improvement of ground-motion prediction accuracy is crucial for seismic hazard and risk assessment and engineering practices. Empirically regressed ground-motion prediction equations (GMPEs) are widely used for such purposes in decades. However, the inherent drawbacks of GMPEs, such as the ergodic assumption, lack of near-source observation, and insufficiency to deal with the spatial correlation issue, have motivated geophysicists to find better alternatives. Recent studies on well-recorded earthquakes have illustrated that physics-based simulation (PBS) methods can provide predictions that are comparable to or ever superior to GMPE predictions. The increasing interests in applying PBSs also pose the need to statistically compare these simulations against GMPE predictions or actual observations. We notice the limitations in previous studies focusing on the predictive capability check of PBS. This article is to illustrate how more reasonable check of PBS should be conducted. We consider GMPE works in generally judging the reasonability of PBS, but PBS has the advantage in characterizing the heterogeneity of ground motion of a moderate-to-large earthquake, especially when considering the complexities in fault geometry, regional stress fields, rock properties, surface of the Earth, and site effects. We would rather recommend that, in the future, different GMPEs are only used to preliminarily judge the reasonability of PBS scenarios; then the ground motions simulated by those reasonable PBS scenarios (not limited to one) are further used for the following seismic hazard and risk assessment.
... this framework, several authors have proposed simplified empirical approaches to adjust the ground-motion model (GMM) prediction with narrow-band amplification factors dependent on the pulse period [7][8][9][10][11][12]. This approach is currently the most practical one, and is different from the prior studies that proposed GMMs explicitly including directivity effects in the functional form [13] or models adjusted through broadband scaling factors [5]. ...
... The estimated mean amplification factor µlnAf (obtained by Equation (11) or Equation (12)) can thus be used in conjunction with the reference GMM µlnSA,GMM (converted in natural logarithm units) to compute the mean ground motion prediction corrected for the pulse-like effects (µlnSA,pulse) as follows: μ lnSA,pulse = ln(μ lnSA,GMM * μ lnA f ) = μ lnSA,GMM + μ lnA f (13) Regarding uncertainty, we did not perform a quantification of the total variability associated to the proposed GMM adjusted for the directivity pulse (σlnSA,pulse); thus, for eventual applications we suggest it is conservatively assumed equal to the σ(T) of Equation (7). Indeed, according to the findings of Shashi and Baker [10], the σlnSA,pulse is always lower than the standard deviation of the reference GMM, by a reduction factor dependent on the pulse-period. ...
Article
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Near-source effects can amplify seismic ground motion, causing large demand to structures and thus their identification and characterization is fundamental for engineering applications. Among the most relevant features, forward-directivity effects may generate near-fault records characterized by a large velocity pulse and unusual response spectral shape amplified in a narrow frequency band. In this paper, we explore the main statistical features of acceleration and displacement response spectra of a suite of 230 pulse-like signals (impulsive waveforms) contained in the NESS1 (NEar Source Strong-motion) flat-file. These collected pulse-like signals are analyzed in terms of pulse period and pulse azimuthal orientation. We highlight the most relevant differences of the pulse-like spectra compared to the ordinary (i.e., no-pulse) ones, and quantify the contribution of the pulse through a corrective factor of the spectral ordinates. Results show that the proposed empirical factors are able to capture the amplification effect induced by near-fault directivity, and thus they could be usefully included in the framework of probabilistic seismic hazard analysis to adjust ground-motion model (GMM) predictions.
... However, since the spectra maintain the Brune-style shape, the model is applicable and the average over many azimuth and takeoff angles reduces the bias to an acceptable value. In fact, the amplitude variation in the forward direction is larger than in the backward direction, and the average of the directivity effect over azimuth is close to but not zero (see Rowshandel, 2010 andSpudich &Chiou, 2008). However, the resulting bias is negligible compared to random estimate fluctuations. ...
... However, since the spectra maintain the Brune-style shape, the model is applicable and the average over many azimuth and takeoff angles reduces the bias to an acceptable value. In fact, the amplitude variation in the forward direction is larger than in the backward direction, and the average of the directivity effect over azimuth is close to but not zero (see Rowshandel, 2010 andSpudich &Chiou, 2008). However, the resulting bias is negligible compared to random estimate fluctuations. ...
Article
Full-text available
We investigate the variability of Brune stress drop (∆σ) and apparent stress (τa) of 23 earthquakes occurred in a small crustal volume adjacent to the hypocenter of the destructive Mw 6.1 L'Aquila earthquake. Their magnitude range is 2.7 ≤ Mw ≤ 4.1. Interevent variability of stress drop and apparent stress results in a factor of 10, well beyond the individual‐event uncertainty. Radiation efficiency ηsw = τa/∆σ varies mostly between 0.1 and 0.2, but in the days immediately before and after the main shock, ηsw tends to be smaller decreasing to values as low as 0.06. This may be the consequence of ruptures migrating in those days into a focal volume with higher dynamic strength. The temporal change of ηsw is tentatively interpreted as a spatial variation due to the earthquake migration into the locked portion of the fault that originated the main shock. Consistently, no variation in stress drop and apparent stress is observed between foreshocks and aftershocks but the smallest and largest ∆σ result in a good correlation with the largest and smallest b‐values, respectively, imaged by other authors in the rupture nucleation volume.
... Rupture directivity is a source effect that results from the interaction of the slip direction with the rupture propagation direction (Spudich and Chiou, 2008). Ground-motion amplitudes will depend on the source-to-site azimuth; seismic waves originating from the forward propagation direction will have higher amplitudes and shorter durations, whereas waves originating from the backward direction will have lower amplitudes and longer durations (Haskell, 1964). ...
... Earthquake directivity effects, observed in more than one-third of the study events, have implications for the strength and frequency content of ground motions, and thus impact the associated hazard. In general, ground motions will have shorter duration, higher corner frequency, and stronger high-frequency content in the forward propagation direction (e.g., Spudich and Chiou, 2008;Spudich et al., 2014;Wang et al., 2017). This means that ground motions could be significantly higher than the median at some azimuths, especially at high frequencies. ...
Article
Full-text available
The Western Canada sedimentary basin (WCSB) has experienced an increase in seismicity during the last decade due primarily to hydraulic fracturing. Understanding the ground motions of these induced earthquakes is critical to characterize the increase in hazard. Stress drop is considered an important parameter in this context because it is a measure of the high‐frequency content of the shaking. We use the empirical Green’s function (EGF) method to determine S‐wave corner frequencies and stress drops of 87 earthquakes of moment magnitude (⁠M⁠) 2.3–4.4 in the WCSB. The EGF method is an effective technique to isolate earthquake source effects by dividing out the path and site components in the frequency domain, using a smaller collocated earthquake as an EGF. The corner frequency of the target event is determined for an assumed spectral ratio shape, from which the stress drop is computed. Assuming a fixed velocity, we find that the average stress drop for induced earthquakes in the WCSB for small‐to‐moderate events is 7.5±0.5 MPa⁠, with a total range from 0.2 to 370 MPa. However, because of the dependence of stress drop on model conventions and constants, we consider the absolute stress‐drop value meaningful only for comparison with other results using the same underlying models. By contrast, corner frequency is a less‐ambiguous variable with which to characterize the source spectrum. The range of corner frequencies obtained in this study for events of M 4.0±0.5 is 1.1–5.8 Hz. Significant rupture directivity is observed for more than one‐third of the earthquakes, with station corner frequencies varying by about a factor of 4 with azimuth. This emphasizes the importance of having suitable station coverage to determine source parameters. We model directivity where evident using a Haskell source model and find that the rupture azimuths are primarily oriented approximately north–south throughout the region.
... In the NGA-west2 guidelines (Spudich et al., 2013), the directivity effect is modelled by isochrone theory (Bernard and Madariaga, 1984;Spudich and Chiou, 2008) or the azimuth between epicentre and site (Somerville et al., 1997). We use the latter approach and model directivity for estimated energy and corrected Arias intensity in a simplified way: ...
... The forward-directivity waves contain a very strong lowfrequency pulse (Fig. 8). The pulse amplitude depends on the ratio of rupture and shear wave velocity and the length of the rupture (Spudich and Chiou, 2008). The forward-directivity pulse is superimposed by high-frequency signals in acceleration traces but becomes more prominent in velocity traces (Baker, 2007) due to its low-frequency nature, i.e. below 1.6 Hz (Somerville et al., 1997). ...
Article
Full-text available
The propagation of a seismic rupture on a fault introduces spatial variations in the seismic wave field surrounding the fault. This directivity effect results in larger shaking amplitudes in the rupture propagation direction. Its seismic radiation pattern also causes amplitude variations between the strike-normal and strike-parallel components of horizontal ground motion. We investigated the landslide response to these effects during the 2016 Kumamoto earthquake (Mw 7.1) in central Kyushu (Japan). Although the distribution of some 1500 earthquake-triggered landslides as a function of rupture distance is consistent with the observed Arias intensity, the landslides were more concentrated to the northeast of the southwest–northeast striking rupture. We examined several landslide susceptibility factors: hillslope inclination, the median amplification factor (MAF) of ground shaking, lithology, land cover, and topographic wetness. None of these factors sufficiently explains the landslide distribution or orientation (aspect), although the landslide head scarps have an elevated hillslope inclination and MAF. We propose a new physics-based ground-motion model (GMM) that accounts for the seismic rupture effects, and we demonstrate that the low-frequency seismic radiation pattern is consistent with the overall landslide distribution. Its spatial pattern is influenced by the rupture directivity effect, whereas landslide aspect is influenced by amplitude variations between the fault-normal and fault-parallel motion at frequencies < 2 Hz. This azimuth dependence implies that comparable landslide concentrations can occur at different distances from the rupture. This quantitative link between the prevalent landslide aspect and the low-frequency seismic radiation pattern can improve coseismic landslide hazard assessment.
... In the NGA-west2 guidelines (Spudich et al., 2013), the directivity effect is modeled by isochrone theory (Bernard and Madariaga, 1984;Spudich and Chiou, 2008) or the azimuth between epicenter and site (Somerville et al., 1997). We use the latter approach and model directivity for estimated energy and corrected Arias intensity in a simplified way: ...
... The forward-directivity waves contain a very strong low-frequency pulse (Figure 4.8). The pulse amplitude depends on the ratio of rupture and shear wave velocity and the length of the rupture (Spudich and Chiou, 2008). The forward-directivity pulse is superimposed by high-frequency signals in acceleration traces but becomes more prominent in velocity traces (Baker, 2007) due to its low-frequency nature, i.e. below 1.6 Hz (Somerville et al., 1997). ...
Thesis
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Landslides are frequent natural hazards in rugged terrain, when the resisting frictional force of the surface of rupture yields to the gravitational force. These forces are functions of geological and morphological factors, such as angle of internal friction, local slope gradient or curvature, which remain static over hundreds of years; whereas more dynamic triggering events, such as rainfall and earthquakes, compromise the force balance by temporarily reducing resisting forces or adding transient loads. This thesis investigates landslide distribution and orientation due to landslide triggers (e.g. rainfall) at different scales (6-4∙10^5 km^2) and aims to link rainfall movement with the landslide distribution. It additionally explores the local impacts of the extreme rainstorms on landsliding and the role of precursory stability conditions that could be induced by an earlier trigger, such as an earthquake. Extreme rainfall is a common landslide trigger. Although several studies assessed rainfall intensity and duration to study the distribution of thus triggered landslides, only a few case studies quantified spatial rainfall patterns (i.e. orographic effect). Quantifying the regional trajectories of extreme rainfall could aid predicting landslide prone regions in Japan. To this end, I combined a non-linear correlation metric, namely event synchronization, and radial statistics to assess the general pattern of extreme rainfall tracks over distances of hundreds of kilometers using satellite based rainfall estimates. Results showed that, although the increase in rainfall intensity and duration positively correlates with landslide occurrence, the trajectories of typhoons and frontal storms were insufficient to explain landslide distribution in Japan. Extreme rainfall trajectories inclined northwestwards and were concentrated along some certain locations, such as coastlines of southern Japan, which was unnoticed in the landslide distribution of about 5000 rainfall-triggered landslides. These landslides seemed to respond to the mean annual rainfall rates. Above mentioned findings suggest further investigation on a more local scale to better understand the mechanistic response of landscape to extreme rainfall in terms of landslides. On May 2016 intense rainfall struck southern Germany triggering high waters and landslides. The highest damage was reported at the Braunsbach, which is located on the tributary-mouth fan formed by the Orlacher Bach. Orlacher Bach is a ~3 km long creek that drains a catchment of about ~6 km^2. I visited this catchment in June 2016 and mapped 48 landslides along the creek. Such high landslide activity was not reported in the nearby catchments within ~3300 km^2, despite similar rainfall intensity and duration based on weather radar estimates. My hypothesis was that several landslides were triggered by rainfall-triggered flash floods that undercut hillslope toes along the Orlacher Bach. I found that morphometric features such as slope and curvature play an important role in landslide distribution on this micro scale study site (<10 km^2). In addition, the high number of landslides along the Orlacher Bach could also be boosted by accumulated damages on hillslopes due karst weathering over longer time scales. Precursory damages on hillslopes could also be induced by past triggering events that effect landscape evolution, but this interaction is hard to assess independently from the latest trigger. For example, an earthquake might influence the evolution of a landscape decades long, besides its direct impacts, such as landslides that follow the earthquake. Here I studied the consequences of the 2016 Kumamoto Earthquake (MW 7.1) that triggered some 1500 landslides in an area of ~4000 km^2 in central Kyushu, Japan. Topography, i.e. local slope and curvature, both amplified and attenuated seismic waves, thus controlling the failure mechanism of those landslides (e.g. progressive). I found that topography fails in explaining the distribution and the preferred orientation of the landslides after the earthquake; instead the landslides were concentrated around the northeast of the rupture area and faced mostly normal to the rupture plane. This preferred location of the landslides was dominated mainly by the directivity effect of the strike-slip earthquake, which is the propagation of wave energy along the fault in the rupture direction; whereas amplitude variations of the seismic radiation altered the preferred orientation. I suspect that the earthquake directivity and the asymmetry of seismic radiation damaged hillslopes at those preferred locations increasing landslide susceptibility. Hence a future weak triggering event, e.g. scattered rainfall, could further trigger landslides at those damaged hillslopes.
... In the NGA-west2 guidelines (Spudich et al., 2013), the directivity effect is modeled by isochrone theory (Bernard and Madariaga, 1984;Spudich and Chiou, 2008) or the azimuth between epicenter and site (Somerville et al., 1997). We use the latter approach and model directivity for estimated energy and corrected Arias intensity in a simplified way: ...
... The forward directivity waves contain a very strong low frequency pulse (Fig. 8). The pulse amplitude depends on the ratio of rupture and shear wave velocity and the length of the rupture (Spudich and Chiou, 2008). The forward directivity pulse is superimposed by high frequency signals in acceleration traces but becomes more prominent in velocity traces (Baker, 2007), due to its low frequency nature, i.e. below 1.6 Hz (Somerville et al., 1997). ...
Preprint
Full-text available
The propagation of a seismic rupture on a fault introduces spatial variations in the seismic wavefield surrounding the fault during an earthquake. This directivity effect results in larger shaking amplitudes in the rupture propagation direction. Its seismic radiation pattern also causes amplitude variations between the strike-normal and strike-parallel components of horizontal ground motion. We investigated the landslide response to these effects during the 2016 Kumamoto earthquake (MW 7.1) in central Kyūshū (Japan). Although the distribution of some 1,500 earthquake-triggered landslides as function of rupture distance is consistent with the observed Arias intensity, the landslides are more concentrated to the northeast of the southwest-northeast striking rupture. We examined several landslide susceptibility factors: hillslope inclination, median amplification factor (MAF) of ground shaking, lithology, land cover, and topographic wetness. None of these factors can sufficiently explain the landslide distribution or orientation (aspect), although the landslide headscarps coincide with elevated hillslope inclination and MAF. We propose a new physics-based ground motion model that accounts for the seismic rupture effects, and demonstrate that the low-frequency seismic radiation pattern consistent with the overall landslide distribution. The spatial landslide distribution is primarily influenced by the rupture directivity effect, whereas landslide aspect is influenced by amplitude variations between the fault-normal and fault-parallel motion at frequencies 2Hz. This azimuth-dependence implies that comparable landslide concentrations can occur at different distances from the rupture. This quantitative link between the prevalent landslide aspect and the low-frequency seismic radiation pattern can improve coseismic landslide hazard assessment.
... It is critical to distinguish the site into near-fault and far-field areas when selecting suitable ground motions to represent seismic hazard for use in site response research. Spudich and Chiou (2008) recommended focusing on inside the domain of ≥ 6.0 and ≤ 40 km for evaluating pulse probability. An empirical relationship for estimating pulse probability was established by Shahi and Baker (2011). ...
Conference Paper
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It is critical to assess seismic risks and determine their site effects in order to reduce damage to buildings in earthquake-prone regions. Recognizing a site as near-fault or far-field is critical for selecting appropriate ground motions for use in the site response analysis (SRA). The dynamic soil parameters of Burdur city center, which is situated inside the tectonically active Fethiye Burdur Fault Zone (FBFZ), were studied in this research using one-dimensional equivalent linear site response analysis (1-D ELSRA), with the near fault effect taken into account. The aim of this study is to assess 1-D ELSRA for Burdur city center. Seismic hazard analysis was performed using deterministic approach and target spectrum for the bedrock level was developed. In this study, 14 real earthquake motion records were selected considering the near fault effect, scaled to the target spectrum and used in the SRA that were performed by the DEEPSOIL computer program. Performing SRA, peak ground acceleration (PGA), 0.2-second and 1-second spectral acceleration, predominant period, and amplification maps of the study area were created as part of the research.
... The distinctive feature of near fault pulse-like records is the presence of one or several strong pulses with large amplitude in velocity time-history (Somerville et al. 1997;Spudich and Chiou 2008). These strong Abstract Pulse-like ground motions may have only a distinct strong pulse or multiple pulses within the velocity time-history. ...
Article
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Pulse-like ground motions may have only a distinct strong pulse or multiple pulses within the velocity time-history. These intrinsic pulses are hidden in low-frequency components that can impose extreme seismic demands on structures. This study presents a simple approach based on the empirical Fourier decomposition (EFD) to extract the intrinsic pulses of pulse-like ground motions. Based on the proposed approach, first, the original ground velocity is decomposed into several Fourier spectrum components (FSCs) via the EFD method. Among these FSCs, the significant low-frequency components are identified based on a proposed relative energy indicator (Ere). Ere is defined as the ratio of the Fourier square amplitude of the FSC to that of the original ground velocity. Next, pulse component is obtained by superimposing the minimum number of significant low-frequency components so that their total energy is above than 70% of the original ground velocity energy. Finally, the strong pulse is extracted from the pulse component by the peak point method. Results obtained by the EFD decomposed method are compared to those obtained from wavelet method for 91 pulse-like ground motions. The results show that the proposed method can extract the intrinsic pulses of pulse-like ground motions with reasonable accuracy. The proposed approach is further applied for classification of near-fault pulse-like ground motions in a dataset of ground motion records. According to the classification results, ground motions with a relative energy value greater than 0.30 can be characterized as pulse-like. Highlights • The intrinsic pulses of pulse like ground motions are extracted based on the empirical Fourier decomposition (EFD) technique. • The Fourier component with the high relative energy can be considered as significant low-frequency component. • Ground motions with Ep values above 0.30 are considered as pulse-like ground motions.
... Readers are directed to the works of Karthik Reddy et al. [26]; Somala et al. [51], where stations are placed in similar race-track locations. While the former reported the ductility demand of inelastic response of simple sdof in conjunction with the Bayless and Somerville [52] and Direct Point [53] directivity parameters, the latter extended this study to compute fragility analysis of 2 span single-column box girder skew bridges. Furthermore, the risk assessment computed for commercial steel frames corresponding to various storey heights by Payyappilly et al. [54] demonstrated variability even in terms of economic loss and injury estimation depending on their location around the fault. ...
Article
Directionality is prominent in the fault normal component of ground motion. It has a different effect on stations in the rupture direction on the tectonic fault than it does on stations in the opposite direction. Such pulse-like features observed in forward and backward directivity stations affect both low-rise and high-rise structures, depending on their fundamental period and the pulse period of ground motion. However, systematic availability of both forward and backward directivity ground motion for unilateral and bilateral earthquakes of the same magnitude at a similar rupture distance for a given fault is rare. So, multiple directivity scenarios are simulated using fracture mechanics-based principles. Using OpenSees, steel moment-resisting frames of 1, 5, and 9 stories, well designed according to building codes, are modeled, and their non-linear response is evaluated. Stations at constant rupture distances are used to compute fragility for each scenario separately. Variation inter-storey drift and peak floor acceleration, along with the hysteretic behavior of panel-zone springs, have also been studied for each of the directivity scenarios. Finally, the results obtained are compared to what is expected by HAZUS.
... However, ground motions close to faults display extremely different characteristics, such as hanging wall effect and directivity effect (Somerville et al. 1997;Wang et al. 2002). Among them, the long period and large amplitude of velocity pulse greatly increase the probability of structural damage under destructive earthquakes (Somerville 2003;Spudich and Chiou 2012), for example, Chi-Chi earthquake (1999), Kocaeli and Duzce earthquake (1999), Wenchuan earthquake (2008), etc. ...
Article
A novel model is constructed to investigate the coupling effect of pulse period (Tp) and peak pulse velocity (Vp) on structural demands with the varied fundamental period (T1) under pulse-like ground motions. The Gaussian function is proposed to quantitatively describe the bell-shape curve of column ductility demand in terms of ln(T1/Tp). Further investigation reveals that the two critical parameters of Gaussian function, i.e. the height of the curve’s peak and the position of the center of the peak, are significantly influenced by Vp, and analytically illustrated by Power function and Boltzmann function, respectively. verification of the proposed two-dimensional structure-pulse coupling model exhibits its accuracy and feasibility in predicting the seismic demand conditioned on vector-valued intensity measure ([Vp, ln(T1/Tp)]) under pulse-like ground motion. Moreover, the coupling model can be used to identify and quantify the response regularity, for instance, the phenomenon that the center position of the peak shifts from 1.0 to 0.5 by increasing Vp is analytically captured in this study. Lastly, the coupling model is also capable to identify the unfavorable range of structural parameters, which is quite practical for near-fault seismic design and risk assessment.
... It is termed as forward-directivity effect due to the propagation of the rupture toward the recording site [1,8]. Pulse-like ground motions are caused mainly by the forward-directivity effect, which are observed at a site when the fault rupture propagates toward the site with a velocity close to shear wave velocity [9,10]. Nevertheless, it should be noted that not all pulse-like ground motions are the result of forward-directivity effects and the appearance of pulses is likely caused by effects other than forward-directivity, such as basins effects, surface wave effects or surficial soil effects [11][12][13][14]. ...
Article
The seismic assessment of steel gabled frames (SGFs) is of great importance and a key problem in any high seismicity region, given the enormous costs of industrial equipment and the remarkable number of individuals working in such structures. Near-fault ground motions, especially their strike-normal component that usually contain a long-period pulse in the velocity time-history, can lead to a significant demand in these structures in comparison to the far-fault ground motions. Although numerous studies have confirmed the destructive effects of near-fault ground motions on concrete and steel structures, no research has been devoted to the impact of these ground motions on steel gabled structures yet. Hence, the findings of this research can unveil novel dimensions of such structures. In this regard, in the present paper, an incremental dynamic analysis (IDA) was conducted for the first time on four SGFs with the spans of 20 m and 60 m and heights of 6 m and 12 m using far-fault ground motions (OR set), as well as near-fault ground motions along the strike-normal and strike-parallel components (SN and SP sets, respectively). The results were presented in the form of multi-record IDA curves, summarized IDA curves, probabilistic seismic demand models (PSDMs) and probabilistic seismic demand analysis (PSDA)curves. The outcomes indicated that compared to far-fault ground motions, near-fault ground motions (especially pulse-like ones) produced significant changes on the seismic behavior of long-period SGFs, resulting in raises the changes of stiffness and demand sensitivity, reduces the dynamic capacity, enhances the data dispersion and uncertainty, and increases the mean annual frequencies (MAFs) in such structures. However, the results of PSDA analysis showed that under any type of ground motion (OR, SN and SP), short-period SGFs are more vulnerable than long-period SGFs and should be prioritized for retrofitting. Finally, the importance of combining the hazard curve of the study region with the results of IDA analysis of the structure in evaluating the seismic behavior of SGFs is highlighted.
... Due to these challenges, other parameters have been used to infer on the possible existence of isotropic source components. Examples include large P/S amplitude ratios (Castro & Ben-Zion, 2013;Castro et al., 1991), reduced directivity effects of high-frequency waves (Spudich & Chiou, 2008), and strong transient rotation of double-couple (DC) focal mechanisms (Ross & Ben-Zion, 2013). The recent increase of high-quality near-fault seismic data improved the ability to derive reliable source mechanisms of earthquakes, some of which include considerable explosive isotropic components (Hayashida et al., 2020;Ross et al., 2015;Stierle et al., 2014). ...
Article
Full-text available
We investigate the non-double-couple components of 224 M ≥ 3.0 earthquakes in the 2019 M_w7.1 Ridgecrest sequence, which occurred on a complex fault system in the Eastern California Shear Zone. Full moment tensors are derived using waveform data from near-fault and regional stations with a generalized cut-and-paste inversion and 3-D velocity and attenuation models. The results show limited Compensated Linear Vector Dipole components, but considerable explosive isotropic components (5%–15% of the total moments) for approximately 50 earthquakes. Most of these events occur between the M_w6.4 foreshock and 1 day after the M_w7.1 mainshock and are mainly distributed around the rupture ends and fault intersections. The percentage of isotropic components is reduced considerably when data recorded by near-fault stations are not included in the inversions, highlighting the importance of near-fault data. The results suggest that high-frequency damage-related radiation and other local dilatational processes are responsible for the observed isotropic source terms.
... We finally selected the following GMPEs: four for active shallow and oceanic crust (Zhao 2006;Cauzzi and Faccioli 2008;Chiou and Youngs 2008;Akkar and Bommer 2010) (Campbell 2003;Cauzzi and Faccioli 2008;Spudich and Chiou 2008;Akkar and Bommer 2010); the model developed by Toro (2002, unpublished) was selected as it is an update of that by Toro et al. (1997). For in-slab and interface subduction earthquakes we selected four models (Youngs et al. 1997;Atkinson and Boore 2003;Zhao 2006;Lin and Lee 2008), and one for volcanic and swarm type areas (Faccioli et al. 2010). ...
Article
Full-text available
The 2013 European Seismic Hazard Model (ESHM13) results from a community- based probabilistic seismic hazard assessment supported by the EU-FP7 project “Seismic Hazard Harmonization in Europe” (SHARE, 2009–2013). The ESHM13 is a consistent seismic hazard model for Europe and Turkey which overcomes the limitation of national borders and includes a through quantification of the uncertainties. It is the first completed regional effort contributing to the “Global Earthquake Model” initiative. It might serve as a reference model for various applications, from earthquake preparedness to earthquake risk mitigation strategies, including the update of the European seismic regulations for building design (Eurocode 8), and thus it is useful for future safety assessment and improvement of private and public buildings. Although its results constitute a reference for Europe, they do not replace the existing national design regulations that are in place for seismic design and construction of buildings. The ESHM13 represents a significant improvement compared to previous efforts as it is based on (1) the compilation of updated and harmonised versions of the databases required for probabilistic seismic hazard assessment, (2) the adoption of standard procedures and robust methods, especially for expert elicitation and consensus building among hundreds of European experts, (3) the multi-disciplinary input from all branches of earthquake science and engineering, (4) the direct involvement of the CEN/TC250/SC8 committee in defining output specifications relevant for Eurocode 8 and (5) the accounting for epistemic uncertainties of model components and hazard results. Furthermore, enormous effort was devoted to transparently document and ensure open availability of all data, results and methods through the European Facility for Earthquake Hazard and Risk (www.efehr.org).
... that is, NGA-West2 and NGA-East. This research program developed new robust GMMs including typical near-fault features (Spudich and Chiou, 2008;Rowshandel, 2010;Shahi and Baker, 2011), which, however, required the specification of source parameters in addition to standard predictive ones (such as slip direction, focal mechanism parameters, and so forth) that are scarcely available in current public repositories of strong-motion records. ...
Article
We present an extended and updated version of the worldwide NEar-Source Strong-motion (NESS) flat file, which includes an increased number of moderate-to-strong earthquakes recorded in epicentral area, new source metadata and intensity measures, comprising spectral displacements and fling-step amplitudes retrieved from the extended baseline correction processing of velocity time series. The resulting dataset consists of 81 events with moment magnitude ≥ 5:5 and hypocentral depth shallower than 40 km, corresponding to 1189 three-component waveforms, which are selected to have a maximum source-to-site distance within one fault length. Details on the flat files, metadata, and ground-motion parameters, processing scheme, and statistical findings are presented and discussed. The analysis of these data allows recognizing the presence of distinctive features (such as pulse-like waveforms, large vertical components, and hanging-wall effects) that can be exploited to assess their impact on near-source seismic motion. As an example, we use the NESS2.0 dataset for calibrating an empirical correction factor of a regional ground-motion model (GMM) mainly based on far-field records. In this way, we can adjust the median predictions to account for near-source effects not fully captured by the reference model. The final goal of this work is to promote the use of the NESS2 flat file as a tool to disseminate qualified and referenced near-source data and metadata in the light of improving the constraints of GMMs (both empirical and physics-based) close to the source. KEY POINTS • We propose an extended version of the worldwide NEar-Source Strong motion flat file (NESS2). • The new dataset exhibits the typical near-source features.
... 1. Forward directivity (Somerville et al. 1997;Somerville 2003Somerville , 2005Spudich and Chiou 2008), 2. Fling step effect, 3. Similar rupture velocity and shear-wave velocity of the bedrock of the site of interest. ...
Article
Full-text available
Near-fault ground motions may contain impulse behavior on velocity records. To calculate the probability of occurrence of the impulsive signals, a large dataset is collected from various national data providers and strong motion databases. The dataset has a large number of parameters which carry information on the earthquake physics, ruptured faults, ground motion parameters, distance between the station and several parts of the ruptured fault. Relation between the parameters and impulsive signals is calculated. It is found that fault type, moment magnitude, distance and azimuth between a site of interest and the surface projection of the ruptured fault are correlated with the impulsiveness of the signals. Separate models are created for strike-slip faults and non-strike-slip faults by using multivariate naïve Bayes classifier method. Naïve Bayes classifier allows us to have the probability of observing impulsive signals. The models have comparable accuracy rates, and they are more consistent on different fault types with respect to previous studies.
... record and the residual (Res.) component.Salient properties of NF excitations with forward researchers [2][3][4][5][6][7]. Mavroeidis et al. [8] reported that the pulse duration (T ably affects the performance of the SDOF systems. ...
Conference Paper
In this paper, attempts are made to evaluate the effects of the extracted pulses and the residual components of near-fault (NF) pulse-like ground motions on seismic response of setback structures. To this end, nine ten-story steel frames with one-side setbacks are subjected to 55 NF ground shakings and their corresponding components. The effect of the ratio of pulse period to the fundamental period of the structure (TP/T1) is also investigated through conducting incremental dynamic analyses. The results are compared in three hazard levels, namely, OBE, DBE, and MCE. It is concluded that the relative effect of pulse and residual components of NF records depends on the intensity level as well as the ratio of TP to T1. In the OBE hazard level of the studied structures, when TP/T1 is about 0.5, the structural responses are more affected by pulse records, while in the case that TP/T1 is not less than 1, the residual component plays an important role in seismic responses. However, in DBE and MCE hazard levels, when TP/T1 is not about 1, the relative effect of pulse components is greater than the residual records in most of the studied setback frames.
... who applied the directivity correction factors for long periods developed by Spudich and Chiou64 implementing them in four GMPEs to improve the PSHA in F I G U R E 1 0 LEC results as function of the return period according to the different PSHA approaches for three representative sites shown inFigure 8and adopting the Reinforced Concrete (RC) low-rise (LR) vulnerability curve as proposed by Özcebe et al 51 . ...
Article
A set of 3D physics-based numerical simulations (PBS) of possible earthquakes scenarios in Istanbul along the North Anatolian Fault (Turkey) is considered in this paper to provide a comprehensive example of application of PBS to probabilistic seismic hazard (PSHA) and loss assessment in a large urban area. To cope with the high-frequency (HF) limitations of PBS, numerical results are first post-processed by a recently introduced technique based on Artificial Neural Networks (ANN), providing broadband waveforms with a proper correlation of HF and LF portions of ground motion as well as a proper spatial correlation of peak values also at HF, that is a key feature for the seismic risk application at urban scale. Secondly, before application to PSHA, a statistical analysis of residuals is carried out to ensure that simulated results provide a set of realizations with a realistic within-event and between-event variability of ground motion. PBS results are then applied in a PSHA framework, adopting both the "generalized attenuation function" (GAF) approach, and a novel "footprint" (FP) based approach aiming at a convenient and direct application of PBS into PSHA. PSHA results from both approaches are then compared with those obtained from a more standard application of PSHA with empirical ground motion models. Finally, the probabilistic loss assessment of an extended simplified portfolio of buildings is investigated, comparing the results obtained adopting the different approaches: (i) GMPE, (ii) GAF and (iii) FP. Only FP turned out to have the capability to account for the specific features of source and propagation path, while preserving the proper physically-based spatial correlation characteristics, as required for a reliable loss estimate on a building portfolio spatially distributed over a large urban area.
... We finally selected the following GMPEs: four for active shallow and oceanic crust (Zhao 2006;Cauzzi and Faccioli 2008;Chiou and Youngs 2008;Akkar and Bommer 2010) (Campbell 2003;Cauzzi and Faccioli 2008;Spudich and Chiou 2008;Akkar and Bommer 2010); the model developed by Toro (2002, unpublished) was selected as it is an update of that by Toro et al. (1997). For in-slab and interface subduction earthquakes we selected four models (Youngs et al. 1997;Atkinson and Boore 2003;Zhao 2006;Lin and Lee 2008), and one for volcanic and swarm type areas (Faccioli et al. 2010). ...
... (i) Forward directivity (Somerville, , 2005Somerville et al., 1997;Spudich and Chiou, 2008), As mentioned before, impulsive signals may create bigger demands on infrastructure than anticipated by building codes. Impulsive signals may affect the infrastructures as below: ...
Thesis
Full-text available
Increasing number of seismic stations located in close proximity to active faults allows analysis of seismic signals that are recorded in near fault regions. Unique seismic signals, called "impulsive" or "pulse shaped" signals, are captured in velocity waveforms in numerous large magnitude earthquakes. In such waveforms, the earthquake is recorded as a one or several long period high amplitude signals. Long period signals are important in engineering seismology due to their large loads on structures. Ground motion prediction equations and design codes fail to capture the amplitudes in long periods of the impulsive signals. In this thesis impulsive signals and their spatial distribution in near fault regions are investigated. To do that two different algorithms are developed in order to distinguish impulsive signals from non-impulsive signals. Moreover, the probability of the pulse shaped signal occurrence is estimated. In order to investigate the impulsive signals, near fault records from major crustal earthquakes are merged into a dataset. It contains waveforms that are coming from well-known seismogenic zones. Waveforms in the dataset are also analyzed by implementing several previous studies to make a comparison. The first pulse shaped signal classification algorithm is developed using wavelet analysis. Wavelet analysis decomposes the signal into time-frequency domain, which provides the energy variation with time and frequency. The wavelet power spectrum of velocity waveforms are analyzed by using Ricker and Morlet wavelets. A threshold of minimum amplitude is applied. A comparison is made between the total energy of a signal and the energy of the time incidence where peak ground velocity is measured. Furthermore time incidence, where maximum spectral energy is located in time, is also taken into consideration. Energy ratios are used for determination of impulsive signals. It is found that a Ricker wavelet explains the features of the impulsive part of the velocity waveforms more accurately than the Morlet wavelet. It can measure the period of the pulse and the phase shift of the impulsive parts of the waveform. Spectral features of the impulsive signals are also captured successfully using a Ricker wavelet. The second classification algorithm uses convolutional neural networks. In order to train the convolutional neural networks, synthetic impulsive signals are created. A model is developed using real non-impulsive velocity waveforms from the dataset and synthetic impulsive waveforms. Impulsive signals are manually labeled as impulsive or non-impulsive. The trained model is run on the real manually-picked impulsive signals of the dataset and the performance of the convolutional neural network, the wavelet method, and various previously published methods are benchmarked. The convolutional neural networks approach correctly identifies almost 97% of the impulsive signals. Accuracy rate of the model is superior than other models. In order to understand the probability of the impulsive signals on earthquakes, a multi-variate Bayes classifier method is implemented on the dataset. Various information about the fault, earthquake and station are analyzed and 3 parameters that are correlated with the impulsive signals are used for the probability calculations. Probability models are developed for normal, reverse and strike slip faults. The validity of this model is tested on the data set. Developed models can provide pulse probability distributions without requiring earthquake-specific parameters. A relation between the period of the pulses and the moment magnitude is also developed.
... This saturation is a manifestation of the recording site's peak motions being controlled by a relatively smaller part of the causative fault as it is forced to grow in length as magnitude increases. It is dependent on the geometry between the recording site and the isochrons on the fault plane [56,84,85]. The resulting peak ground motions thus start to exhibit a saturation known as deviation from self-similar ground motion scaling, the rate of which appears to increase with magnitude [16]. ...
Article
The Icelandic strong-motion dataset is relatively small and the largest recorded earthquake magnitude is Mw 6.5, whereas events of around Mw 7.0 are known to have occurred in the South Iceland Seismic Zone (SISZ). As a result, the required features for use in probabilistic seismic hazard assessment (PSHA), such as deviation from self-similar magnitude scaling and magnitude-distance dependent saturation of ground motions at larger magnitudes, is challenging. Compounding the issue, GMMs from other seismic regions exhibit a strong bias to the available Icelandic strong-motions, underpredicting in the near-fault and overpredicting in the far-field regions. In this study, we approach this issue by considering several GMMs that have either been used or recommended for PSHA in Iceland or have functional forms that satisfy the minimum requirements of GMMs used in PSHA. We recalibrate these GMMs to fit the Icelandic data in the context of the Bayesian statistical framework and a Markov Chain Monte Carlo (MCMC) algorithm, where model inference is carried out using both non-informative and informative priors for selected model coefficients from the original GMMs. Moreover, we used a random effects model to partition the aleatory variability into inter-event and intra-event components. We show that the GMMs with informative priors for magnitude scaling and magnitude-distance scaling terms, not only capture the high near-fault amplitudes and rapid ground motion attenuation with distance, but also introduce a controlled saturation of large magnitude ground motions, which is consistent with observations in other interplate regions. In this study we also introduce a simple GMM, based on informative priors from a model for magnitude-dependent earthquake depth in the SISZ, that fully captures the salient characteristics of the recalibrated GMMs. The presented models thus form a suite of new, essentially hybrid, empirical GMMs that can be used with confidence in predicting PGA and PSA for Icelandic earthquakes, with particular implications for the reassessment of the seismic hazard of Iceland.
... There are two approaches to incorporate the effects of near-fault earthquakes in the design of infrastructures. In the first approach, near-fault effects are indirectly taken into account by modifications to the elastic acceleration response spectrum (EARS) at 5% damping (Somerville et al. 1997, Somerville 2003, Spudich and Chiou 2008. In this approach, the shape of EARS is amplified by a number which is mainly a function of structures' period. ...
Article
Full-text available
Past severe earthquakes, such as Bam earthquake of 2003 and Tabas earthquake of 1978, have demonstrated that many cities in Iran are prone to be struck by near-fault earthquakes. Such earthquakes are impulsive in nature, and therefore, they are more destructive than the ordinary ground shaking. In the fourth edition of Iranian seismic code (Standard No. 2800), some changes, including a modification factor for the elastic acceleration response spectrum (EARS) have been recently recommended to reflect the effects of such probable near-fault earthquakes for the designing procedure. In this study, a numbers of 2D RC moment resisting frames (MRFs), from four to twelve story buildings, are designed linearly based on Iranian National Building Code (INBC) and Standard No. 2800 as well. Subsequently, their nonlinear models are reproduced for conducting nonlinear dynamic time history (NDTH) analysis. For this purpose, twenty impulsive ground motions are selected and scaled to be compatible with the design basis earthquake (DBE) spectrum of the abovementioned code. It is concluded that the seismic performance of the analyzed structures are not satisfactory at all; no buildings are successful to satisfy the life safety (LS) performance level posed by guidelines such as ASCE41-06 or ASCE41-13. Moreover, it is worth mentioning that even collapse prevention (CP) limit states are not also met in some cases. Therefore, the recently added modifications in the Standard No. 2800 may be inadequate to incorporate the near-fault earthquakes' effects.
... Most of the energy in this kind of ground motion gathers in a narrow frequency band and produces high intensity velocity pulses that are oriented at the fault-normal direction. (Somerville et al. 1997, Somerville 2003, Spudich and Chiou 2008. In reinforced concrete wall buildings, the characteristics of forward directivity NF seismic ground motion lead to a larger seismic demand when compared with the ordinary far-field (FF) seismic ground motion (Beiraghi et al. 2016a-c). ...
Article
Reinforced concrete walls and buckling restrained braces are effective structural elements that are used to resist seismic loads. In this paper, the behavior of the reinforced concrete walls coupled with buckling restrained braces is investigated. In such a system, there is not any conventional reinforced concrete coupling beam. The coupling action is provided only by buckling restrained braces that dissipate energy and also cause coupling forces in the wall piers. The studied structures are 10-, 20- and 30-story ones designed according to the ASCE, ACI-318 and AISC codes. Wall nonlinear model is then prepared using the fiber elements in PERFORM-3D software. The responses of the systems subjected to the forward directivity near-fault (NF) and ordinary far-fault (FF) ground motions at maximum considered earthquake (MCE) level are studied. The seismic responses of the structures corresponding to the inter-story drift demand, curvature ductility of wall piers, and coupling ratio of the walls are compared. On average, the results show that the inter-story drift ratio for the examined systems subjected to the far-fault events at MCE level is less than allowable value of 3%. Besides, incremental dynamic analysis is used to examine the considered systems. Results of studied systems show that, the taller the structures, the higher the probability of their collapse. Also, for a certain peak ground acceleration of 1 g, the probability of collapse under NF records is more than twice this probability under FF records.
... Some recent models go further to account for other factors affecting earthquake ground motions, such as directivity effects (e.g. Rowshandel, 2006;Spudich et al., 2004;Spudich and Chiou, 2008;Rowshandel, 2010;Shahi and Baker, 2011) and hanging wall effects (e.g. Abrahamson and Silva, 1997;McVerry et al., 2006;Abrahamson and Silva, 2008;Chiou and Youngs, 2014). ...
Article
Many years have passed since previous national seismic hazard maps were prepared for South Africa. In those maps, zone-less techniques were applied. The availability of more reliable seismicity and geological data has made it possible to update those maps using probabilistic seismic hazard analysis methodologies that take into consideration all available data. This paper presents a summary of the work conducted to produce the latest seismic hazard maps for South Africa. This involved the systematic compilation and homogenisation of an earthquake catalogue, which comprised both historical and instrumental events. The catalogue played a prominent role in the preparation and characterisation of the seismic source model. Two ground motion prediction equations were identified from available international models for regions that are tectonically similar to South Africa. These two models were then implemented in the hazard calculations, which were done using the OPENQUAKE software. Uncertainties associated with input parameters in both the seismic source and ground motion models were taken into account and implemented using the logic tree technique. Maps showing distribution of acceleration at three periods (0.0s, 0.15s and 2.0s) computed for 10% probability of exceedance in 50 years were produced.
... Even though many studies have shown the significant impact of directivity and have proposed specific GMPEs to account for its effect (e.g. see [68,69]) as well as methodologies to perform PSHA for such sites [70], due to difficulties of these approaches and their need for extra data related to the nearby faults, they have been applied only in specific cases (e.g. [71]). ...
Article
Regional, multi-country seismic hazard models provide a comparison basis for national seismic hazard models that are generally used to underpin the seismic design prescriptions of national building codes. Our study presents an attempt to formalize a framework for performing such a comparison. This comparison consists of sequential steps for identifying and understanding similarities of the key elements informing the seismic hazard models and the code design ground motions in addition to their numerical comparison. The challenge may arise, on one hand, from the lack of transparency of some national seismic codes and, on the other hand, from the intrinsic difficulties in comparing seismic hazard models. In this study, as an example we compare the seismic design spectrum of the Iranian national design code with the uniform hazard spectra from the recent, fully-harmonized, cross-borders Earthquake Hazard Model for the Middle East region (EMME). This comparison focuses on the two 10% in 50-year exceedance probability maps for PGA and on the pairs of design spectra for four cities with different seismicity levels. While, in general, the two reference maps for PGA on rock seem similar, the comparison of the uniform hazard spectra and design spectra for the four selected cities for different soil conditions show large differences. We offer some plausible causes for these differences as well as generic recommendations for overcoming them.
... There are two approaches to incorporate the effects of near-fault earthquakes in the design of infrastructures. In the first approach, near-fault effects are indirectly taken into account by modifications to the elastic acceleration response spectrum (EARS) at 5% damping (Somerville et al. 1997, Somerville 2003, Spudich and Chiou 2008. In this approach, the shape of EARS is amplified by a number which is mainly a function of structures' period. ...
Preprint
Full-text available
Past severe earthquakes, such as Bam earthquake of 2003 and Tabas earthquake of 1978, have demonstrated that many cities in Iran are prone to be struck by near-fault earthquakes. Such earthquakes are impulsive in nature, and therefore, they are more destructive than the ordinary ground shaking. In the fourth edition of Iranian seismic code (Standard No. 2800), some changes, including a modification factor for the elastic acceleration response spectrum (EARS) have been recently recommended to reflect the effects of such probable near-fault earthquakes for the designing procedure. In this study, a numbers of 2D RC moment resisting frames (MRFs), from four to twelve story buildings, are designed linearly based on Iranian National Building Code (INBC) and Standard No. 2800 as well. Subsequently, their nonlinear models are reproduced for conducting nonlinear dynamic time history (NDTH) analysis. For this purpose, twenty impulsive ground motions are selected and scaled to be compatible with the design basis earthquake (DBE) spectrum of the abovementioned code. It is concluded that the seismic performance of the analyzed structures are not satisfactory at all; no buildings are successful to satisfy the life safety (LS) performance level posed by guidelines such as ASCE41-06 or ASCE41-13. Moreover, it is worth mentioning that even collapse prevention (CP) limit states are not also met in some cases. Therefore, the recently added modifications in the Standard No. 2800 may be inadequate to incorporate the near-fault earthquakes' effects.
... Pulse-shape signals can appear in some earthquake scenarios, like those considering forward directivity, which occurs when receivers are located in the forward direction of the fault rupture (Somerville et al. 1997;Somerville 2003Somerville , 2005Spudich and Chiou 2008), the fling step effect, which is a permanent displacement of the ground resulting from fault rupture (Mavroeidis and Papageorgiou 2002) and when rupture velocity and shear-wave velocity of the bedrock of the site of interest are similar. ...
Article
Full-text available
Near fault ground motions may contain impulse behavior on velocity records. Such signals have a particular indicator which makes it possible to distinguish them from non-impulsive signals. These signals have significant effects on structures; therefore, they have been investigated for more than 20 years. In this study, we used Ricker and Morlet wavelets in order to analyze the wavelet power spectrum of the strong motion signals to investigate the impulsiveness. Both the area around the PGV and the area that exceeds the minimum threshold for the energy function are used in order to determine the position of the pulse. On both of these cases, particular criteria are used in order to characterize the signal. Then, we calculate the pulse period of the pulse region. Ricker and Morlet wavelets are also used to mimic the pulse signal. This method provides advanced information about the position of the maximum energy of the pulse part of the signal. We found that the impulsive part of the signal is frequently at the position where PGV occurs and the Ricker wavelet is better than the Morlet wavelet on mimicking the pulse part of the waveform. Spectral responses of strong motion waveform and the wavelets have strong correlation at around pulse period. Results show consistency with previous studies; hence, it can be used as a solid alternative on pulse shape signal investigations.
... Ground motions in seismic hazard assessment are typically described by GMPEs that depend mainly on event magnitude, source-to-site distance, and site effects (e.g., the Vs 30 value), but other source-related and path-related effects may be important, too. However, standard GMPEs fail to describe ground motions of earthquakes with strong directivity effects, varying rupture speed or 3-D velocity structures including low-velocity basins (e.g., Graves et al., 2008;Ramirez-Guzman et al., 2015;Roten et al., 2019;Spudich & Chiou, 2008;. Therefore, dynamic rupture simulations like ours are useful to possibly complement GMPEs by exploring physically possible parameter spaces. ...
Article
Full-text available
The 1992 Mw 7.3 Landers earthquake is perhaps one of the best studied seismic events. However, many aspects of the dynamics of the rupture process are still puzzling, for example, the rupture transfer between fault segments. We present 3‐D spontaneous dynamic rupture simulations, incorporating the interplay of fault geometry, topography, 3‐D rheology, off‐fault plasticity, and viscoelastic attenuation. Our preferred scenario reproduces a broad range of observations, including final slip distribution, shallow slip deficits, and mapped off‐fault deformation patterns. We demonstrate good agreement between synthetic and observed waveform characteristics and associated peak ground velocities. Despite very complex rupture evolution, ground motion variability is close to what is commonly assumed in Ground Motion Prediction Equations. We examine the effects of variations in modeling parameterization within a suite of scenarios including purely elastic setups and models neglecting viscoelastic attenuation. Source dynamics of all models include dynamic triggering over large distances and direct branching; rupture terminates spontaneously on most of the principal fault segments. Sustained dynamic rupture of all fault segments in general, and rupture transfers in particular, constrain amplitude and orientation of initial fault stresses and friction. We conclude that physically consistent in‐scale earthquake rupture simulations can augment earthquake source observations toward improving the understanding of earthquake source physics of complex, segmented fault systems.
... Since the occurrence of pulse-like motions depends on the geometry of the site and the fault (e.g., Iervolino andCornell 2008, Shahi andBaker 2011), it may not be suitable to apply the FN (FP) direction in all site-specific cases. Heyden et al. (2014) once used the isochrones directivity predictor (IDP) (Spudich and Chiou 2008) to examine the preferred orientation, and they concluded that although the forward-directivity-induced pulses on average tend to be orientated along the FN direction, uncertainty usually exists with regard to the orientation of any single motion. Several other studies (Kalkan and Kwong 2013, Reyes and Kalkan 2015a, Reyes and Kalkan 2015b) also draw similar conclusions that, for a given ground motion pair, the use of the FN (FP) or MD direction does not always yield conservative nonlinear responses. ...
Article
Near-fault ground motions can impose particularly high seismic demands on structures due to the pulses that are typically observed in the velocity time-histories. In this study it is empirically found that the critical response can be estimated from the directions corresponding to the maximum (max) or minimum (min) pulse-energy. Determination of the pulse-energy requires removing of the high-frequency content. For achieving this, the wavelet analysis and the least-square-fitting (LSF) algorithm are adopted. Results obtained by the two strategies are compared and differences between them are analyzed. Finally, the relationship between the critical response and the response derived from directions having the max or min pulse-energy confirms that using the pulse-energy for deriving the critical response of the building structures is reasonable.
... In FD ground motions, the energy from the fault rupture arrives at the nearfault site in the form of one or more large pulses, which results in a large seismic demand on a structure [3][4][5][6][7][8][9][10][11][12]. Near-fault pulse-like ground motions have both higher IM levels than non-pulse ground motions and produce higher responses for the same IM level compared to non-pulse ground motions [2,[13][14][15][16]. ...
Article
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Ground motions at sites close to a fault are sometimes affected by forward directivity, where the rupture energy arrives at the site in a form of a very short duration pulse. These pulses impose a heavy demand on structures located in the vicinity of the fault. In this research a probabilistic seismic demand analysis (PSDA) for a self-centering bridge is carried out. The bridge columns consisted of unbonded post-tensioned concrete filled fiber reinforced polymer tubes. A bridge model was developed and non-linear time history analyses were performed. Three different methodologies that use spectral accelerations to predict structural response was used and a time domain approach was used for PSDA. In addition to the three approaches, a time domain PSDA methodology was also used. The results of the PSDA from the four approaches are compared, and the advantages of using the time domain methodology are discussed. The results of the PSDA showed that for a site located very close to the fault (6 km in this study), earthquakes having as small magnitude (Mw) as 6.5 can have significant contribution to the hazard because the periods of pulses generated by small magnitude earthquake coincide with the period of the bridge. Since the small magnitude events occur with greater frequency than large magnitude events they can have high contribution to the hazard.
... Conventional ground motion models (GMMs) do not explicitly account for the characteristics of near-fault ground motions such as velocity pulses (e.g., Somerville et al. 1997, Ambraseys andDouglas 2003); however, having such records in the databases utilized for developing GMMs implicitly influences their resulting predictions (Shahi andBaker 2011, Spudich et al. 2014). Attempts have been made to modify the prediction of conventional GMMs in order to explicitly account for directivity effects by using posthoc modifications (e.g., Somerville et al. 1997, Somerville 2003, Tothong et al. 2007, Spudich and Chiou 2008, Shahi and Baker 2011. A more rigorous approach to address this problem is the direct consideration of the near-fault characteristics in the development of GMMs (e.g., Shahi 2013, Chiou and, which requires improvements in existing directivity models ). ...
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This paper focuses on the selection of ground motions for seismic response analysis in the near-fault region, where directivity effects are significant. An approach is presented to consider forward directivity velocity pulse effects in seismic hazard analysis without separate hazard calculations for 'pulse-like' and 'non-pulse-like' ground motions, resulting in a single target hazard (at the site of interest) for ground motion selection. The ability of ground motion selection methods to appropriately select records which exhibit pulse-like ground motions in the near-fault region is then examined. Applications for scenario and probabilistic seismic hazard analysis cases are examined through computation of conditional seismic demand distributions and the seismic demand hazard. It is shown that ground motion selection based on an appropriate set of intensity measures (IMs) will lead to ground motion ensembles with an appropriate representation of the directivity-included target hazard in terms of IMs, which are themselves affected by directivity pulse effects. This alleviates the need to specify the proportion of pulse-like motions and their pulse periods a priori as strict criteria for ground motion selection.
... Other studies focused instead on providing modification factors to already available GMPEs to account for the pulse effects. 1,5,6 To include these GMPEs in probabilistic seismic hazard analysis of near-fault sites, many researchers 5,[7][8][9][10][11][12][13] have tried to obtain the probability of occurrence of pulse-like records at a specific site depending on the geometry of the site with respect to the likely rupture orientation in nearby faults. But how often do pulses occur in near fault recordings? ...
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Based on the assumption that directivity effect is mainly a function of the fraction of ruptured area toward the site, I presented a directivity model that generalizes the earlier model of Somerville et al. (1997). The directivity effect is simply defined in terms of one rupture parameter ξ (which depends on fault geometry, a rupture initiation point, and site location), a free coefficient C1, and a directivity coefficient C2 (which is dependent on the period and the soil type). The model is tested extensively using faults of different sizes and geometry, including single-segment strike-slip and dip-slip, and also multisegment strike-slip and dip-slip faults. The NGA data and four attenuation relations were used to compute the two coefficients in the model. Specifically, the directivity coefficients for ground motions in rock and in soil for periods up to 3 s were determined. It is found that rupture directivity effect is present in ground motions at all periods. However, the effect becomes significant at 0.3 s and increases with the period, at least up to a period of 3 s (for which this study was done), and likely beyond that, although with a lower rate. Based on an analysis of the uncertainty, I found that correcting for directivity would result in a decrease of the attenuation standard error term, sigma, by as much as 10%. Based on these results, I conclude that local variations in the near-source ground motions, especially at longer periods, should be partly attributed to rupture directivity. I also investigated the dependence of fault-normal and fault-parallel spectral accelerations in the NGA database on rupture direction. The results showed a strong dependence of FN/FP and FN/AVE acceleration ratios on rupture directivity, especially for long periods. The model can also be used to investigate the effect of rupture heterogeneity on ground motions. Information on fault rupture heterogeneities during earthquakes, such as various features of asperities, distributions of slip, slip-rate, stress drop, etc., can be used to conduct such an investigation. Further study should involve a more detailed analysis of the effects of rupture on near-source ground motions, particularly in terms of fault-parallel and fault-normal components, taking into account the effects of heterogeneities and comparing predicted ground motions with recorded ground motions for various earthquakes.
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We present a model for estimating horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The model provides predictive relationships for the orientation-independent average horizontal component of ground motions. Relationships are provided for peak acceleration, peak velocity, and 5-percent damped pseudo-spectral acceleration for spectral periods of 0.01 to 10 seconds. The model represents an update of the relationships developed by Sadigh (1997) and incorporates improved magnitude and distance scaling forms as well as hanging-wall effects. Site effects are represented by smooth functions of average shear wave velocity of the upper 30 m (V-S30) and sediment depth. The new model predicts median ground motion that is similar to Sadigh (1997) at short spectral period, but lower ground motions at longer periods. The new model produces slightly lower ground motions in the distance range of 10 to 50 km and larger ground motions at larger distances. The aleatory variability in ground motion amplitude was found to depend upon earthquake magnitude and on the degree of nonlinear soil response, For large magnitude earthquakes, the aleatory variability is larger than found by Sadigh (1997).
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Empirical ground-motion models for the rotation-independent average horizontal component from shallow crustal earthquakes are derived using the PEER NGA database. The model is applicable to magnitudes 5-8.5, distances 0-200 km, and spectral periods of 0-10 sec. In place of generic site categories (soil and rock), the site is parameterized by average shear-wave velocity in the top 30 m (V-S30) and the depth to engineering rock (depth to V-S=1000 m/s). In addition to magnitude and style-of-faulting, the source term is also dependent on the depth to top-of-rupture: for the same magnitude and rupture distance, buried ruptures lead to larger short-period ground motions than surface ruptures. The hanging-wall effect is included with an improved model that varies smoothly as a function of the source properties (M, dip, depth), and the site location. The standard deviation is magnitude dependent with smaller magnitudes leading to larger standard deviations. The short-period standard deviation model for soil sites is also distant-dependent due to nonlinear site response, with smaller standard deviations at short distances.
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This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the "PEER NGA" (Pacific Earthquake Engineering Research Center's Next Generation Attenuation) project. For periods less than 1s , the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude M, closest horizontal distance to the surface projection of the fault plane RJB, and the time-averaged shear-wave velocity from the surface to 30 m VS30. The equations are applicable for M =5-8 , RJB 200 km, and VS30= 180- 1300 m / s. DOI: 10.1193/1.2830434
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We use a database of more than 80 finite-source rupture models for more than 50 earthquakes (Mw 4.1–8.1) with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip. Rupture in strike-slip and crustal dip-slip earthquakes tends to nucleate in the deeper sections of the fault; subduction earthquakes do not show this tendency. Ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement. Rupture nucleates in regions of very large slip (D ≥ 2/3 Dmax) in only 16% of the events, in regions of large slip (1/3 Dmax < D < 2/3 Dmax) in 35% of the events, and in regions of low slip (D ≤ 1/3 Dmax) in 48% of the events. These percentages significantly exceed the percentages of fault area with very large (∼7%) and large (∼28%) slip. Ruptures that nucleate in regions of low slip, however, tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length. Applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip.
Earthquake Spectra, submitted Simulation of ground motion scaling characteristics for the Modification of empirical strong ground motion attenuation relations to include the amplitude and duration effects of rupture directivity
  • — Somerville
  • P G Collins
  • N Graves
  • R Pitarka
  • A Silva
  • W Zeng
  • Y Nga
––—, 2008. Directivity in NGA ground motions based on four NGA relations, Earthquake Spectra, submitted. Somerville, P. G., Collins, N., Graves, R., Pitarka, A., Silva, W., and Zeng, Y., 2006. Simulation of ground motion scaling characteristics for the NGA-E Project, Proceedings of the 8th Na-tional Conference on Earthquake Engineering, San Francisco, California. Somerville, P. G., Smith, N. F., Graves, R. W., and Abrahamson, N. A., 1997. Modification of empirical strong ground motion attenuation relations to include the amplitude and duration effects of rupture directivity, Seismol. Res. Lett. 68, 199–222.
The distribution of modified Mercalli intensity in the San Francisco, earthquake, Bull. Seismol. Soc. Am Ground motion prediction equations for the average horizontal component of PGA, PGV, and 5%-damped PSA at spectral periods between 0
  • J Boatwright
  • H Bundock
  • D M Boore
  • G A Atkinson
Boatwright, J., and Bundock, H., 2008. The distribution of modified Mercalli intensity in the April 18, 1906, San Francisco, earthquake, Bull. Seismol. Soc. Am., 98, 890–900, DOI: 10.1785/0120060404. Boore, D. M., and Atkinson, G. A., 2008. Ground motion prediction equations for the average horizontal component of PGA, PGV, and 5%-damped PSA at spectral periods between 0.01 s and 10.0 s, Earthquake Spectra 24, 99–138.
Effects of rupture directivity on probabilistic seismic hazard analysis
  • N Abrahamson
Abrahamson, N., 2000. Effects of rupture directivity on probabilistic seismic hazard analysis, Proceedings from the 6th International Conference on Seismic Zonation, Palm Springs, California.
Abrahamson & Silva NGA ground motion relations for the geometric mean horizontal component of peak and spectral ground motion parameters
  • N Abrahamson
  • W Silva
Abrahamson, N., and Silva, W., 2007. Abrahamson & Silva NGA ground motion relations for the geometric mean horizontal component of peak and spectral ground motion parameters, PEER Report, Pacific Earthquake Engineering Research Center, 378 pp. ---, 2008. Summary of the Abrahamson & Silva NGA ground motion relations, Earthquake Spectra 24, 67-97.
Campbell-Bozorgnia NGA horizontal ground motion model for PGA, PGV, PGD, and 5% damped linear elastic response spectra
  • K C Campbell
  • Y Bozorgnia
Campbell, K. C., and Bozorgnia, Y., 2008. Campbell-Bozorgnia NGA horizontal ground motion model for PGA, PGV, PGD, and 5% damped linear elastic response spectra, Earthquake Spectra 24, 139-171.
Directivity in preliminary NGA residuals
  • P Spudich
  • B Chiou
Spudich, P., and Chiou, B. S-J., 2006. Directivity in preliminary NGA residuals, Final Project Report for PEER Lifelines Program Task 1M01, available at http://quake.usgs.gov/~spudich/ pdfs_for_web_page/Spudich&Chiou1M01_FinalReport-v6.pdf, 49 pp. ---, 2008. See EPAPS Document No. E-EASPEF-24-112803 for electronic appendices. For more information on EPAPS, see http://www.aip.org/pubservs/epaps.html.
E-EASPEF-24-112803 for electronic appendices. For more information on EPAPS, see http://www.aip.org/pubservs/epaps A formulation of directivity for earthquake sources using isochrone theory
  • – Spudich
  • P Chiou
  • J Graves
  • R Collins
  • N Somerville
––—, 2008. See EPAPS Document No. E-EASPEF-24-112803 for electronic appendices. For more information on EPAPS, see http://www.aip.org/pubservs/epaps.html. Spudich, P., Chiou, B. S-J., Graves, R., Collins, N., and Somerville, P. G., 2004. A formulation of directivity for earthquake sources using isochrone theory, U.S. Geological Survey Open File Report 2004-1268, available at http://pubs.usgs.gov/of/2004/1268/.
Modification of ground motion prediction equations for the effects of rupture directivity, Earthquake Spectra, submitted
  • J Watson-Lamprey
Watson-Lamprey, J., 2008. Modification of ground motion prediction equations for the effects of rupture directivity, Earthquake Spectra, submitted. (Received 18 July 2007; accepted 28 November 2007͒
Simulation of ground motion scaling characteristics for the NGA-E Project
  • P G Somerville
  • N Collins
  • R Graves
  • A Pitarka
  • W Silva
  • Y Zeng
Somerville, P. G., Collins, N., Graves, R., Pitarka, A., Silva, W., and Zeng, Y., 2006. Simulation of ground motion scaling characteristics for the NGA-E Project, Proceedings of the 8th National Conference on Earthquake Engineering, San Francisco, California.
The distribution of modified Mercalli intensity in the
  • J Boatwright
  • H Bundock
Boatwright, J., and Bundock, H., 2008. The distribution of modified Mercalli intensity in the April 18, 1906, San Francisco, earthquake, Bull. Seismol. Soc. Am., 98, 890-900, DOI: 10.1785/0120060404.
A formulation of directivity for earthquake sources using isochrone theory
  • P Spudich
  • B. S-J Chiou
  • R Graves
  • N Collins
  • P G Somerville
Spudich, P., Chiou, B. S-J., Graves, R., Collins, N., and Somerville, P. G., 2004. A formulation of directivity for earthquake sources using isochrone theory, U.S. Geological Survey Open File Report 2004-1268, available at http://pubs.usgs.gov/of/2004/1268/.
  • Frazer