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Impact of Earthquake Depth on Basin Response

Voon Hui Lai, Robert W. Graves, & Donald V. Helmberger

Published August 15, 2017, SCEC Contribution #7806, 2017 SCEC Annual Meeting Poster #235

Seismic observations from two similar magnitude events (Mw 4.4) with strike-slip mechanisms near Fontana but at different depths (3.5 km and 14.2 km) yield very different response at high and low frequency across the Los Angeles Basin. The deeper event generated more high frequency content and was widely felt, as shown by USGS Did-You-Feel-It (DYFI) reports as compared to the shallower event. A comparable DYFI response is also observed between larger magnitude events such as the shallow 2014 M5.1 La Habra event and the deep 2008 M5.5 Chino Hills event. The shallower Fontana event, however, generated stronger low frequency surface waves (2 – 50 seconds) which lasted for a much longer duration for many stations in LA Basin, up to 150 seconds. Waveforms from an aftershock (Ml 3.1) of the shallow event, at a similar depth, correlate with the main event very well, emphasizing the effect of velocity structure and demonstrating the relatively simple nature of the source. We are currently running 3D simulations of these events using both CVM-H and CVM-S4.26 to investigate how well these models can replicate the observed elongated duration. Additionally, we consider the role 3D stochastic perturbations to the seismic velocity structure and other shallow structures may play in generating these waveform characteristics, particularly as the simulations are pushed to higher frequencies (> 1 Hz).

Lai, V., Graves, R. W., & Helmberger, D. V. (2017, 08). Impact of Earthquake Depth on Basin Response. Poster Presentation at 2017 SCEC Annual Meeting.

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SCEC Community Models (CXM)