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In Situ Vp/Vs Ratios During the 2019 Ridgecrest Earthquake Sequence

Description: 

The ratio of compressional- to shear-wave velocity (Vp/Vs) is directly related to Poisson’s ratio and can provide insights into characterizing crack and fluid properties and analyzing the effect of pore fluid pressure. In this study, we apply a high-resolution estimation method using waveform cross-correlation data to calculate in situ Vp/Vs ratios in the near-source regions of the 2019 Ridgecrest seismic sequence and to investigate the spatial and temporal patterns in Vp/Vs ratio. We take advantage of the waveform cross-correlation relocation catalog and differential times for 29,462 earthquakes from January 1 to August 31, 2019 from an earlier study originated from the seismic data at the Southern California Earthquake Data Center. Over 164 million P- and S-wave differential times and the corresponding correlation coefficients for 1 million event pairs are available for the estimation of in situ Vp/Vs ratios. The most prominent feature in our results is the relatively homogeneous ratio throughout the majority of the rupture zone of the earthquake sequence. Slightly lower values are seen in the areas where the seismic activity ceased. An intriguing observation is the relatively high Vp/Vs ratios surrounding the source regions of the Mw 6.4 and 7.1 earthquakes. The Coso Geothermal Field is dominated with very low Vp/Vs values. From there, the Vp/Vs ratios gradually increase to the northwest direction. We will compare our results with the tomographic models and other geophysical data to investigate the fault zone material and associated stress characteristics of near source regions.

Session: Crustal Imaging of High Seismic Hazard Regions

Type: Oral

Date: 4/20/2023

Presentation Time: 08:45 AM (local time)

Presenting Author: Guoqing Lin

Student Presenter: No

Invited Presentation: 

Authors