Ricardo Taborda

Computational modeling has greatly contributed in recent years to the understanding of the effects of the source, wave propagation path, and site effects on earthquake ground motion in urban regions. Due in part to computational limitations and to limitations in the knowledge of the seismic velocities at the required scales, deterministic modeling of ground motion in realistic basins has been restricted to maximum frequencies of about 0.5 Hz. For engineering applications, however, it is necessary to simulate ground motion to much higher frequencies, say up to 10 Hz. Even though stochastic methods have been developed for this purpose, it is nonetheless desirable to be able to extend the range of applicability of deterministic methods beyond current limits, both regarding frequency and cutoff values of the shear wave velocity. A comparison of synthetic seismograms with corresponding observations from earthquakes could help determine the actual limits of deterministic modeling. Results of the simulations can also give additional insight into the spatial and temporal distribution of ground motion for a wide range of frequencies of practical interest.

In this study we describe a scalable, finite element octree-based parallel toolchain for wave propagation modeling developed by the Quake group at Carnegie Mellon University and use it to model the strong shaking over an extended region in Los Angeles and surrounding regions expected from a Mw 7.7 southern San Andreas earthquake. The region and scenario earthquake are similar to the TeraShake 1.3 simulations conducted at SCEC by Olsen et al (2006), except that we consider maximum frequencies up to 1 Hz and minimum shear wave velocities of 300 m/s, instead of 0.5 Hz and 500 m/s used in the earlier studies. We examine the effects of these parameters on individual seismograms and on the peak ground motion, as well as on Fourier and response spectra, in an effort to identify directivity effects and major amplifications associated with characteristic frequencies of the basins.