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Title: Upper Crustal Structure and Magmatism in Southwest Washington: V p , V s , and V p / V s Results From the iMUSH Active‐Source Seismic Experiment
Authors:
 ;  ;  ;  ;  
Publication Date:
NSF-PAR ID:
10385165
Journal Name:
Journal of Geophysical Research: Solid Earth
Volume:
124
Issue:
7
Page Range or eLocation-ID:
p. 7067-7080
ISSN:
2169-9313
Publisher:
DOI PREFIX: 10.1029
Sponsoring Org:
National Science Foundation
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  1. SUMMARY

    We present our estimations and comparisons of the in situ Vp/Vs ratios and seismicity characteristics for the Parkfield segment of the San Andreas fault in northern California and the San Jacinto Fault Zone and its adjacent regions in southern California. Our results show that the high-resolution in situ Vp/Vs ratios are much more complex than the tomographic Vp/Vs models. They show similar variation patterns to those in the tomographic Vp models, indicating that Vp/Vs ratios are controlled by material properties but are also strongly influenced by fluid contents. In Parkfield, we observe velocity contrasts between the creeping and locked sections. In southern California, we see small-scale anomalous Vp/Vs variation patterns, especially where fault segments intersect, terminate and change orientations. In addition, our investigation confirms that the seismicity in Parkfield is more repeatable than in southern California. However, the earthquakes in the southernmost portion of the San Andreas fault, the trifurcation area of the San Jacinto Fault Zone and the Imperial fault are as much likely falling into clusters as those in Parkfield. The correlation of highly similar events with anomalous in situ Vp/Vs ratios supports the important role of fluids in the occurrence of repeating earthquakes. The high-resolution Vp/Vs ratio estimation methodmore »and the corresponding results are helpful for revealing roles of fluids in driving earthquake, fault interaction and stress distribution in fault zones.

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