Is Ground‐Motion Variability Distance Dependent? Insight from Finite‐Source Rupture Simulations

Imtiaz, Afifa; Causse, Mathieu; Chaljub, Emmanuel; Cotton, Fabrice

doi:10.1785/0120140107

Cited by 16 publications

(7 citation statements)

References 27 publications

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Section: Discussionsupporting

confidence: 82%

“…Our estimates of the intraevent ϕ lnPGV for R JB 11 km (ϕ lnPGV ∼ 0:6-1:0) are consistent with those of Imtiaz et al (2015) for unilateral ruptures (ϕ lnPGV ∼ 0:5-1:0). Imtiaz et al (2015) also found distance dependence of ϕ lnPGV , which they interpreted to be a consequence of the directivity effect. In our study, we develop a quantitative understanding of the distance decay of ϕ lnPGV from a statistical point of view (by fitting a functional form) as well as a physical point of view (by analyzing effect of rupture parameters).…”

Section: Discussionsupporting

confidence: 82%

“…They also discovered that the correlation of ϕ lnY with magnitude and distance is not consistent across different spectral periods. Imtiaz et al (2015) found that the intraevent ϕ lnY also shows distance dependence with rupture style: for bilateral ruptures, ϕ lnY tends to increase with distance, whereas for unilateral ruptures, ϕ lnY tends to decrease with distance. Youngs et al (1995) reported that ϕ lnY decreases with increasing magnitude and that the magnitude dependence is stronger for the interevent ϕ lnY than for the intraevent ϕ lnY .…”

Section: Introductionmentioning

confidence: 99%

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Distance and Azimuthal Dependence of Ground‐Motion Variability for Unilateral Strike‐Slip Ruptures

Vyas¹,

Martin²,

Gális³

2016

Bulletin of the Seismological Society of America

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We investigate near-field ground-motion variability by computing the seismic wavefield for five kinematic unilateral-rupture models of the 1992 M w 7.3 Landers earthquake, eight simplified unilateral-rupture models based on the Landers event, and a large M w 7.8 ShakeOut scenario. We include the geometrical fault complexity and consider different 1D velocity-density profiles for the Landers simulations and a 3D heterogeneous Earth structure for the ShakeOut scenario. For the Landers earthquake, the computed waveforms are validated using strong-motion recordings. We analyze the simulated ground-motion data set in terms of distance and azimuth dependence of peak ground velocity (PGV).Our simulations reveal that intraevent ground-motion variability ϕ lnPGV is higher in close distances to the fault (< 20 km) and decreases with increasing distance following a power law. This finding is in stark contrast to constant sigma-values used in empirical ground-motion prediction equations. The physical explanation of a large near-field ϕ lnPGV is the presence of strong directivity and rupture complexity. High values of ϕ lnPGV occur in the rupture-propagation direction, but small values occur in the direction perpendicular to it. We observe that the power-law decay of ϕ lnPGV is primarily controlled by slip heterogeneity. In addition, ϕ lnPGV , as function of azimuth, is sensitive to variations in both rupture speed and slip heterogeneity. The azimuth dependence of the ground-motion mean μ lnPGV is well described by a Cauchy-Lorentz function that provides a novel empirical quantification to model the spatial dependency of ground motion.Online Material: Figures of slip distributions, residuals to ground-motion prediction equations (GMPEs), distance and azimuthal dependence, and directivity predictor of ground-motion variability for different source models.

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Section: Discussionsupporting

confidence: 82%

Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Distance and Azimuthal Dependence of Ground‐Motion Variability for Unilateral Strike‐Slip Ruptures

Vyas¹,

Martin²,

Gális³

2016

Bulletin of the Seismological Society of America

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“…Hence, the variability decreases and it is mainly controlled by the radiation pattern shape and site complexities. Similar observations have been made by Imtiaz et al (2015) and by Vyas et al (2016) though for different magnitude and distance ranges.…”

Section: Discussionsupporting

confidence: 87%

Regional broad-band ground-shaking modelling over extended and thick sedimentary basins: an example from the Lower Rhine Embayment (Germany)

Pilz

Cotton

Razafindrakoto

et al. 2020

Bull Earthquake Eng

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The simulation of broad-band (0.1 to 10 + Hz) ground-shaking over deep and spatially extended sedimentary basins at regional scales is challenging. We evaluate the ground-shaking of a potential M 6.5 earthquake in the southern Lower Rhine Embayment, one of the most important areas of earthquake recurrence north of the Alps, close to the city of Cologne in Germany. In a first step, information from geological investigations, seismic experiments and boreholes is combined for deriving a harmonized 3D velocity and attenuation model of the sedimentary layers. Three alternative approaches are then applied and compared to evaluate the impact of the sedimentary cover on ground-motion amplification. The first approach builds on existing response spectra ground-motion models whose amplification factors empirically take into account the influence of the sedimentary layers through a standard parameterization. In the second approach, site-specific 1D amplification functions are computed from the 3D basin model. Using a random vibration theory approach, we adjust the empirical response spectra predicted for soft rock conditions by local site amplification factors: amplifications and associated ground-motions are predicted both in the Fourier and in the response spectra domain. In the third approach, hybrid physics-based ground-motion simulations are used to predict time histories for soft rock conditions which are subsequently modified using the 1D site-specific amplification functions computed in method 2. For large distances and at short periods, the differences between the three approaches become less notable due to the significant attenuation of the sedimentary layers. At intermediate and long periods, generic empirical ground-motion models provide lower levels of amplification from sedimentary soils compared to methods taking into account site-specific 1D amplification functions. In the near-source region, hybrid physics-based ground-motions models illustrate the potentially large variability of ground-motion due to finite source effects.

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“…To examine the increase in the forecast accuracy with data assimilation time, we calculated the GMRotD50 (Boore et al, 2006), the median velocity response spectra of horizontal components for a given period in rotating the orientation of horizontal components from 0° to 90°, for the forecasted waveforms at a period of 8 s. The GMRotD50 has recently been used to assess the strength of the ground motions independent of the direction of the epicenter (e.g., Barani et al, 2015; Imtiaz et al, 2015). The GMRotD50 ratio relative to that of the expected ground motion is shown in Figure 10d, confirming that the ratio increases gradually from 15% to 60% with increasing data assimilation time from 30 to 90 s. After 100 s, the GMRotD50 ratio increased suddenly to nearly 100% as the rupture of the earthquake fault plane had been completed (section S4 for snapshots of the seismic wave propagation).…”

Section: Real‐time Forecasting Of the Lp Ground Motions For Large Nanmentioning

confidence: 99%

Data Assimilation‐Based Early Forecasting of Long‐Period Ground Motions for Large Earthquakes Along the Nankai Trough

2020

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Long-period (LP) ground motions with periods of~2-10 s caused by large earthquakes are strongly amplified in sedimentary basins, posing serious threats to modern cities to cause resonance and damage to skyscrapers, oil storage tanks, long-span bridges, and other structures with long natural periods. Since the LP ground motions are composed of surface waves traveling for longer distances with much slower speeds than body waves, an alert could be issued by detecting the spread of strong ground motion near the source and before large ground motions occur in distant basins. In this study, an early forecasting of LP ground motions is proposed based on data assimilation of observed ground motions obtained by high-density, nationwide seismic networks and a computer simulation of the seismic wave propagation using a high-resolution subsurface structure model. The shaking of the LP ground motions in the distant basins is immediately forecasted by high-speed supercomputers from current data-assimilated wavefield. In addition, the forecasting speed is significantly improved by using Green's functions, representing the wave propagation response from the data assimilation stations to a forecast target site. The effectiveness of this data assimilation-based forecasting of LP ground motions in conjunction with using Green's functions is demonstrated by numerical tests using the observed strong motion records from the 2004 Off Kii Peninsula earthquake in Japan (Mw 7.4) together with synthetic seismograms of anticipated large earthquake scenarios in the Nankai Trough.

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Is Ground‐Motion Variability Distance Dependent? Insight from Finite‐Source Rupture Simulations

Cited by 16 publications

References 27 publications

Distance and Azimuthal Dependence of Ground‐Motion Variability for Unilateral Strike‐Slip Ruptures

Distance and Azimuthal Dependence of Ground‐Motion Variability for Unilateral Strike‐Slip Ruptures

Regional broad-band ground-shaking modelling over extended and thick sedimentary basins: an example from the Lower Rhine Embayment (Germany)

Data Assimilation‐Based Early Forecasting of Long‐Period Ground Motions for Large Earthquakes Along the Nankai Trough

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