Distance and Azimuthal Dependence of Ground‐Motion Variability for Unilateral Strike‐Slip Ruptures
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
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AbstractWe investigate near‐field ground‐motion variability by computing the seismic wavefield for five kinematic unilateral‐rupture models of the 1992 Mw 7.3 Landers earthquake, eight simplified unilateral‐rupture models based on the Landers event, and a large Mw 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 Graphic 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 Graphic is the presence of strong directivity and rupture complexity. High values of Graphic occur in the rupture‐propagation direction, but small values occur in the direction perpendicular to it. We observe that the power‐law decay of Graphic is primarily controlled by slip heterogeneity. In addition, Graphic, as function of azimuth, is sensitive to variations in both rupture speed and slip heterogeneity. The azimuth dependence of the ground‐motion mean μln(PGV) 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.
CitationDistance and Azimuthal Dependence of Ground‐Motion Variability for Unilateral Strike‐Slip Ruptures 2016, 106 (4):1584 Bulletin of the Seismological Society of America
SponsorsWe thank Rob Graves for providing us with the source model of the ShakeOut scenario and Paul Spudich for sharing with us his MATLAB scripts to compute the directivity corrections. We thank Fabrice Cotton for his critical review that helped us to improve the manuscript. We also thank Kiran Kumar Thingbaijam for insightful discussions. The research presented in this article is supported by King Abdullah University of Science and Technology (KAUST) in Thuwal, Saudi Arabia. Earthquake rupture and ground‐motion simulations have been carried out using the KAUST Supercomputing Laboratory (KSL), and we acknowledge the support of the KSL staff.
PublisherSeismological Society of America (SSA)