How stressed are we really? Harnessing community models to characterize the crustal stress field in Southern California

Karen M. Luttrell

Published October 11, 2016, SCEC Contribution #6459, 2016 SCEC Annual Meeting Talk on 9/12 14:30 (PDF)

The in situ crustal stress field fundamentally governs, and is affected by, the active tectonic processes of plate boundary regions, yet questions remain about the characteristics of this field and the implications for active faults in the upper crust. We investigate the nature of this stress field in southern California by combining observations from the SCEC Community Stress Model, including stress orientation, stress from topography, and stress accumulation rate on major locked faults. First, we estimate the magnitude of the non-lithostatic in situ stress field in southern California by balancing in situ orientation indicated by earthquake focal mechanisms against the stress imposed by topography, which tends to resist the motion of strike-slip faults. Our results indicate that most regions require in situ differential stress of at least 20 MPa at seismogenic depth. In the areas of most rugged topography along the San Andreas Fault System, differential stress at seismogenic depth must exceed 62 MPa consistent with differential stress estimates from complimentary methods. Second, we assess the origin of the heterogeneity observed in the stress field by combining stress accumulation on major locked fault segments with stress from topography and a simple 2-D tectonic driving stress. Our results suggest that in situ stress heterogeneity at the regional scale is more influenced by deep driving processes acting on a laterally heterogeneous crust than by perturbations to the stress field associated with major locked faults in the upper crust. Finally, we discuss some potential avenues for moving toward a 4D representation of the crustal stress field in southern California.

Citation
Luttrell, K. M. (2016, 10). How stressed are we really? Harnessing community models to characterize the crustal stress field in Southern California. Oral Presentation at 2016 SCEC Annual Meeting.

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