Finite-Difference Wave Simulation of High-Frequency Seismic Waveforms in the Cascadia Subduction Zone

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

The goal of this study is to simulate high-frequency seismic waveforms recorded by ocean bottom seismometers within the Juan de Fuca plate, and ultimately to provide a high-resolution crustal-scale seismic velocity model. The first P-arrivals of air-gun shots from the active-source experiment MGL1211 provide high-quality crustal phase Pg or head wave Pn signals at a frequency range of 4-40 Hz. The signal-to-noise ratio of the first P-arrivals generally decreases with increasing source-to-receiver distance, from deep to shallow water, with increasing sediment thickness and decreasing air-gun shot spacing and time interval. We don’t observe strong correlations between the data quality and the air-gun array depth. We simulate the wave propagation at a narrow frequency range of 4-6 Hz using the finite-difference method with a 3-D reference model generated based on the recent active-source work in Cascadia. We apply a ricker pulse with a half width of 0.3 s as the source-time function of the vertical force. Our preliminary tests show a good match of the first P-arrivals between the observed and synthetic data with less than 1-second phase delays and cross-correlation coefficients >= 0.7. Our next step of this study is to perform a joint inversion of high-frequency air-gun shot signals and short-period ambient noises within the Juan de Fuca plate. The tomographic results of a joint inversion will provide a tight constraint of the structure from the shallowest sedimentary layers down to tens of kilometers, filling the gap in the model resolution between active- and passive-source seismic tomographic images.

Presenting Author: Sampath Rathnayaka

Authors