Spatio-temporal variations of stress parameters in the San Jacinto Fault Zone

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

Submitted August 9, 2017, SCEC Contribution #7457, 2017 SCEC Annual Meeting Poster #207

We discuss variations of stress parameters in the San Jacinto Fault Zone based on a refined stress inversion methodology [Martínez-Garzón, 2016a] and a focal mechanism catalog for the years 1981-2015 (Yang et al. 2012, extended to 2015). The stress inversion provides the principal stress orientations and the stress ratio parameter R = (σ1-σ2)/(σ1-σ3). We first analyze the depth variations of stress parameters in three sections of the fault zone, Crafton Hills (CH), Hot Springs area (HS) and Trifurcation area (TR). Then we examine possible temporal changes associated with the 2010 Mw 7.2 El Mayor-Cucapah earthquake in the HS and TR regions by analyzing and comparing two sub-catalogs for the years 2008-2009 and 2011-2012.

The obtained spatial distribution of stress parameters is in general in agreement with the tectonic setting and the regional geology. Clear variations in the orientation of SHmax and the magnitude of R-value are observed with depth, reflecting overall changes from strike-slip towards transpressional and transtensional regimes below 12 km. The orientation of SHmax rotates clockwise with increasing depth. The maximum SHmax rotation is observed at Crafton Hills and is associated with a change of 23 degrees from the surface to 18 km depth.

The SHmax orientation along the fault remains generally the same before and after the El Mayor-Cucapah earthquake, showing oblique faulting in the Hot Springs and Trifurcation areas. The R-value changes toward transpressional regime in the Trifurcation area after the El Mayor-Cucapah event. Updated results including also correlations between the stress changes and potency tensors will be presented in the meeting.

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

Citation
Abolfathian, N., Martínez-Garzón, P., & Ben-Zion, Y. (2017, 08). Spatio-temporal variations of stress parameters in the San Jacinto Fault Zone. Poster Presentation at 2017 SCEC Annual Meeting.


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