SCEC Award Number 19221 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title High-F Project: Verification and Validation of the M5.1 La Habra, CA, Earthquake
Investigator(s)
Name Organization
Kim Olsen San Diego State University
Other Participants Zhifeng Hu (PhD student, SDSU/UCSD)
SCEC Priorities 4a, 4b, 4c SCEC Groups GM, EEII, CS
Report Due Date 04/30/2020 Date Report Submitted 04/29/2020
Project Abstract
 We have carried out a series of 0-5 Hz finite-difference simulations of the 2014 M5.1 La Habra, CA, earthquake, in an extraction of the SCEC CVM-S4.26-M01. We find that ground accelerations are biased lower if material with Vs less than 200 m/s is set to 500 m/s (median Vs30 value for sites in domain is 280 m/s), thus we include the lower velocities in our simulations. Models with topography as the only added feature tend to generate stronger ground shaking, as compared those with a flat free surface. The beneficial effects of small-scale heterogeneities (SSHs) as the only added feature are minor in terms of improving the fit for the Cumulative Absolute Velocity (CAV) with data, where the main effect is to lower the peak motions and extend the duration. The models with topography only and topography + SSHs generally tend to improve the fit for the CAV with data. Overall, Qs=50 Vs (Vs in km/s) provides a better fit than those using Qs=100 Vs. Moreover, the addition of frequency-dependent attenuation with Q(f)= 50V_s*f^0.4 increases the amplitudes of the synthetics, in particular at the higher frequencies (2.5-5 Hz), which can help improve the CAV fit. Thus, preliminary results suggest that Vs(min)=200 m/s, SSHs, topography, and Q(f) all contribute toward a better fit and should be included in future modeling. Current efforts and future plans include generating maps of goodness-of-fit (GOF) for different ground motion metrics, and using a larger model domain.
Intellectual Merit The results of this project enable us to understand better the prospects of accurately modeling higher frequency ground motions using primarily deterministic simulations. In addition, they illuminate the relative importance of model features, such as topography, small-scale crustal heterogeneities, and frequency-dependent anelastic attenuation. The project is part of SCEC's 'High-f' collaborative exercises.
Broader Impacts This work has funded and enabled a PhD student to be trained in high-performance computing and 3D finite difference modeling. The results provide valuable guidance as to which model features (such as near-surface, low velocity material, topography, small-scale crustal velocity perturbations, and frequency-dependent attenuation) are important for ground motion estimation at various frequency bands.
Exemplary Figure Figure 6. Comparison of (left) synthetic seismograms and (right) CAV to data for different models at station 14 ( epicentral distance of 19.24 km) for two different bandwidths: a) 0.15 to 2.5 Hz, and b) 2.5 to 5 Hz. Credits: Zhifeng Hu.