Dr. Kim Bak Olsen and William Savran’s poster presentation for the Seismological Society of America 2014 Annual Meeting in Anchorage, Alaska

Session: Recent Advances in Ground Motions Simulation Methods and Their Validation

Deterministic Simulation of the Mw 5.4 Chino Hills Event with Frequency-Dependent Attenuation, Heterogeneous Velocity Structure and Realistic Source Model
SAVRAN, W. H., San Diego State University, San Diego, CA, USA, wsavran@ucsd.edu; OLSEN, K. B., San Diego State University, San Diego, CA, USA, kbolsen@mail.sdsu.edu
We present simulations of the 2008 Mw 5.4 Chino Hills earthquake for frequencies 0.1 to 2.5Hz. Our model includes frequency-dependent attenuation with power law Q(f)=Q0fn (Withers et al., 2013), statistical models of small-scale heterogeneities in the medium, and a finite-fault source description (Shao et al., 2012). The background medium is the Southern California Earthquake Center (SCEC) community velocity model version 4 (CVM-4). We generate synthetic seismograms at 14 stations in the Los Angeles Area and perform sensitivity tests on the parameters of the small-scale heterogeneities, guided by analysis of sonic logs. Our results show that key ground motion parameters, such as peak ground velocity (PGV), peak ground acceleration (PGA), cumulative kinetic energy (CKE) and Arias intensity (AI) are affected by the statistical model parameters up to 60% at some stations. End-member tests show that correlation length (L) can change CKE, PGV, and AI by up to 30%. Varying the Hurst exponent (H) from 0.0 to 0.5 causes a slight increase in CKE and AI, but does not result in systematic changes of PGV or PGA. Spectral analysis shows the statistical model primarily affects frequencies greater than 1Hz. Based on comparisons with data, we recommend an attenuation relationship where Qs0=0.10Vs to Qs0=0.15Vs, and statistical models of small-scale heterogeneities with L=150m, H=0.0-0.1 and standard deviations of 5-10%. The statistical models include a horizontal-to-vertical anisotropy factor (~5), based on findings from borehole analysis (Plesch and Shaw, 2013). We find reasonable fits for ground motion parameters and frequency content; however, at some of the stations, particularly on hard-rock sites, the small-scale heterogeneities do not account for the misfit between observed and synthetic seismograms. As a result of this, we conclude the seismic velocities in the upper hundreds of meters are too large in the CVM-4 at these sites.

Thursday, May 1st / Poster #75 / Cook/Arteaga