Variations of stress parameters in the Southern California plate
boundary around the South Central Transverse Ranges
Abstract
We examine stress parameters in Southern California with a focus on the
region near the South Central Transverse Ranges (SCTR), using a refined
stress inversion methodology to 1981-2017 declustered and aftershocks
focal mechanisms independently. Comparison between the associated stress
parameters provides information on the local dominant loading. The
estimated stress parameters are examined in relation to the regional
stress regime and local loadings. Over the regional scale, the Strends
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
deviations from the regional shear stress. The San Bernardino Mountain
area shows S direction towards NNW and transpressional stress components
likely associated with the relative motion of the San Andreas Fault and
ECSZ. The Cajon Pass and San Gorgonio Pass show transpressional stress
regime near the bottom of the seismogenic zones likely associated with
the elevated topography. In Crafton Hills, rotation of the principal
stress plunges and S 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.