Variations of Stress Parameters in the Southern California Plate Boundary Around the South Central Transverse Ranges

Session: Crustal Stress and Strain and Implications for Fault Interaction and Slip
Type: Oral
Date: 4/28/2020
Time: 08:45 AM
Room: 240
Description: 

We examine stress parameters in Southern California with a focus on the region near the South Central Transverse Ranges (SCTR). The results are based on a refined stress inversion methodology employing focal mechanism catalog for the years 1981-2017. The inversions provide the stress ratio R= (σ₁-σ₂)/(σ₁-σ₃) and orientations of the three principal stress axes from which the maximum horizontal compressional stress direction (SHmax) is derived. We apply the inversions to declustered and aftershocks focal mechanisms independently, and comparison between the associated stress parameters provides information on the dominant loading in the examined areas. The estimated spatio-temporal stress parameter distributions are examined in relation to regional stress regime and local loadings such as fault interactions, topography and crustal depth. Over the regional scale, the SHmax trends towards the NNE and the stress ratios vary from transtensional stress regime near the Eastern California Shear Zone (ECSZ) to shear stress near the SCTR and towards transpression near the Western Transverse Ranges. Detailed analysis of stress parameters near the SCTR indicates the following deviations from the expected regional shear stress: (1) The San Bernardino Mountain area shows an SHmax direction towards NNW and transpressional stress components likely associated with the relative motion of the SAF and ECSZ. (2) The Cajon Pass and San Gorgonio Pass show transpressional stress regime near the bottom of the seismogenic zones likely associated with the elevated topography. (3) In Crafton Hills, rotation of the principal stress plunges and SHmax direction and transtensional stress regime below ~10 km, along with lower estimated apparent friction coefficient suggest a weak fault possibly associated with deep creep. The results reveal effects of local loadings resolved by the performed multi-scale analysis. The study does not show significant temporal variations of stress variations near the SCTR from the average stress parameters in the analyzed 37 years.

Presenting Author: Niloufar Abolfathian

Authors