Stress Constraints on Cajon Pass Fault Segments Informed by Focal Mechanism Inversion, Fault Loading, and Topography

Karen M. Luttrell, Elliott C. Helgans, Liliane Burkhard, & Bridget R. Smith-Konter

Published September 11, 2022, SCEC Contribution #12595, 2022 SCEC Annual Meeting Poster #193

Earthquake processes along active faults are strongly influenced by the in situ crustal stress field, which itself is comprised of multiple geophysical processes acting simultaneously at different spatial and temporal scales. We model the in situ stress field at seismogenic depth in Cajon Pass by balancing the orientation of the modern stress field inferred from earthquake focal mechanisms against the superposition of the far field tectonic driving stress, the load of topography, and the accumulation of stress on locked faults over variable loading times. In particular, we consider the resolved normal and shear stresses along six discreetly loaded sections of fault, represented by eleven distinct segments from the SCEC Community Fault Model. The orientation of the modeled 3D stress tensor is assessed in terms of predicted rake direction, azimuth of maximum horizontal stress (SHmax), and Andersonian fault parameter (Aphi), and the characteristics of the resulting stress field is evaluated in terms of resolved normal, strike-slip shear, and dip-slip shear stresses along the fault segments. Results suggest considerable stress heterogeneity along and between fault segments, with resolved normal and shear stresses varying by 15 – 40 MPa along strike. The spatial variation in modeled stress magnitude is considerably more than the range of predicted stress magnitudes at any one location from model non-uniqueness. The resulting range of modeled 3D stress fields can be used both to inform other investigations of stress dependent phenomena and assess the role stress heterogeneity may play in imposing control on large multifault ruptures.

Citation
Luttrell, K. M., Helgans, E. C., Burkhard, L., & Smith-Konter, B. R. (2022, 09). Stress Constraints on Cajon Pass Fault Segments Informed by Focal Mechanism Inversion, Fault Loading, and Topography. Poster Presentation at 2022 SCEC Annual Meeting.

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