Physics-based Prediction of Ground Motions Using Realistic Fault Rupture Models and 3D Geological Structures

Physics-based Prediction of Ground Motions Using Realistic Fault Rupture Models and 3D Geological Structures

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Credit:
K.B. Olsen, S.M. Day, J.B. Minster, Y. Cui, A. Chourasia, D. Okaya, P. Maechling, and T. Jordan, 2008. ©Seismological Society of America

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Description

Ground motion intensities (warm colors correspond to high intensities) for a simulated M 7.7 earthquake with SE to NW rupture on a 200-km section of the San Andreas Fault. Strong rupture directivity and intensity amplification occur due to funneling of seismic waves through sedimentary basins south of the San Bernardino and San Gabriel Mountains. The simulation to the left assumes a kinematic (space-time history of slip being prescribed) rupture model, while the one on the right uses a dynamic (physics-based) rupture. The difference in the predicted intensities in this highly populated region underscores the importance of properly characterizing source processes in such simulations. (Image modified from K.B. Olsen, S.M. Day, J.B. Minster, Y. Cui, A. Chourasia, D. Okaya, P. Maechling, and T. Jordan, 2008. TeraShake2: Spontaneous rupture simulation of Mw 7.7 earthquakes on the Southern San Andreas Fault, Bulletin of the Seismological Society of America, 98(3):1162–1185, ©Seismological Society of America)

Understanding and mitigating earthquake risk depends critically on predicting the intensity of strong ground motion, a daunting scientific challenge. The faulting that generates seismic waves is complex and incompletely understood. Moreover, seismic waves are strongly distorted as they propagate through Earth’s heterogeneous crust, which is incompletely mapped. In practice, strong ground motion is characterized using intensity measures, such as peak ground acceleration, or peak ground velocity, in an attempt to capture damage potential. Earthquake engineering relies on parametric relationships that predict the strength of shaking during future earthquakes, based on how the ground motion during past earthquakes varied with factors such as magnitude, distance to fault rupture, and surficial geology.

This empirical approach is adequate for moderate earthquakes; however, there are very few on-scale recordings near large earthquakes, where the hazard is highest. Physics-based strong ground motion simulations have the potential to fill this gap, but only if they accurately reflect the full range of Earth behaviors in the presence of strong seismic waves. Physics-based ground motion simulation is thus an area of intense research and rapid recent progress. An important element of such simulations is dynamic rupture modeling, which considers the joint stress-slip evolution during earthquake shear failure as being driven by the redistribution of stored strain energy and can serve as the foundation for predicting fault behavior and strong ground motion. Dynamic rupture modeling requires the use of today’s most powerful supercomputers because representations of faults have to span spatial scales covering many orders of magnitude, and because physical quantities must be calculated at all causally connected points to properly account for stress and slip evolution.

Date Taken: February 18, 2009
Photographer / Contributor: K.B. Olsen, S.M. Day, J.B. Minster, Y. Cui, A. Chourasia, D. Okaya, P. Maechling, and T. Jordan, 2008

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Seismological_Grand_Challenges, Long_Range_Science_Plan,

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