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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 method 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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Crustal Architecture Across Southern California and Its Implications on San Andreas Fault Development
Abstract In this study, we perform a 2‐frequency sequential receiver function stacking investigation in Southern California. The resulting Moho depths exhibit similar patterns to previous studies while the crystalline crustal Vp/Vs values show more regional variations. Most Vp/Vs variations can be explained by compositional differences. We observe a dichotomy in Moho depth, Vp/Vs, and crustal strain rates between the Peninsular Ranges and Southern San Andreas Fault system. Comparisons between strain rates, Vp/Vs, and temperature suggest that crustal compositional variations may have played a more critical role in influencing the crustal strain rate variations in the Peninsular Ranges and Southern San Andreas than temperature. The structural and compositional variations provide a new insight into the causes of the migration of the Southern San Andreas Fault system and the formation of the “Big Bend.”
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- Award ID(s):
- 1814051
- PAR ID:
- 10409621
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 8
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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