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Towards Detailed Characterization of Spatio-temporal Variations in Stress Parameters along the San Jacinto Fault Zone

Niloufar Abolfathian, Patricia Martínez-Garzón, & Yehuda Ben-Zion

Published September 9, 2016, SCEC Contribution #6511, 2016 SCEC Annual Meeting Poster #013 (PDF)

Poster Image: 
Accurate determination of stress parameters (orientation of principal stress axes and stress ratio) operating on fault zones provides refined knowledge on source physics and deformation processes. We developed a refined stress inversion methodology using declustered seismicity, to remove events likely affected by local stress interactions rather than reflecting the large-scale background stress field, and discretizing the remaining focal mechanisms using an updated k-means technique [Martínez-Garzón et al., in prep].

In this study we apply the refined stress inversion methodology to obtain a reliable high resolution information of stress parameters throughout the San Jacinto Fault Zone in Southern California. In particular, we investigate potential stress changes along and across the fault and also through the seismogenic depth. The stress parameters are analyzed using two seismicity catalogs containing focal mechanisms before and after the 2010, Mw 7.2 El Mayor-Cucapah earthquake in Baja California, to detect potential stress changes in relation to the occurrence of this event.

The initial results are in agreement with the expected stress type due to the tectonic setting and the geology of the region. Both inversions before and after El Mayor earthquake are generally consistent along the fault, showing transtensional stress regime in the northwestern section and more complex oblique faulting within the main fault traces in the middle and southeastern sections. These results are in agreement with studies by Yang and Hauksson (2013) and Bailey et al. (2010). Changes of stress shape ratio across the fault are observed in selected regions such as the trifurcation area, while the orientation of the maximum horizontal stress is consistent across the fault. The continuing work focuses on potential spatial changes in the stress field related to damage zones and depth, and temporal variations of stress parameters.

Key Words
Stress Inversion, Focal Mechanisms, Stress Variations, San Jacinto Fault Zone

Abolfathian, N., Martínez-Garzón, P., & Ben-Zion, Y. (2016, 09). Towards Detailed Characterization of Spatio-temporal Variations in Stress Parameters along the San Jacinto Fault Zone. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)