SCEC Award Number 20135 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Crustal Stress Models for Cajon Pass with Epistemic Uncertainty and Implications Earthquake Gate Behavior
Investigator(s)
Name Organization
Karen Luttrell Louisiana State University Bridget Smith-Konter University of Hawaii at Manoa
Other Participants Elliott Helgans (LSU)
Liliane Burkhard (UH)
Undergraduate Student Researcher (LSU)
SCEC Priorities 1c, 1d, 1e SCEC Groups SDOT, CXM, SAFS
Report Due Date 03/15/2021 Date Report Submitted 10/08/2024
Project Abstract
 We model the in situ stress field at seismogenic depth in Cajon Pass constrained by the orientation of the modern stress field inferred from earthquake focal mechanisms. We incorporate existing models for stress accumulation rate from locked faults and topography and perform an optimization to determine the range of reasonable regional stress fields that adequately predict the orientation of the in situ stress field along major faults. We find that the predicted rake angles are the most sensitive to differential stress magnitude, providing both lower and upper bounds of ~55–90 MPa. Regional stress orientation exhibits a strong preference for north-south compression with a slightly non-vertical intermediate axis (plunge angle >70º). We use the range of acceptable total stress field models to calculate the resolved stresses along six distinctly-rupturing fault segments in the Cajon Pass area. We find the resolved dip-slip shear stresses are mostly very low (<10 MPa), while resolved normal stresses vary by ~60 MPa along all fault segments. Resolved strike-slip shear stresses vary between ~0-40 MPa along Mission Creek segments, ~20-50 MPa along the main San Andreas segments, and ~20-40 MPa along the San Jacinto segments. In most cases, the variation in stress magnitudes along strike greatly exceeds the range of model-predicted resolved stress values at any one location (typically <15 MPa). This suggests that accurate fault location and orientation information are as important as reasonable 3D stress field orientation and magnitude in determining the resolved stresses along and between faults.
Intellectual Merit These findings directly support the objectives of the Community Models (CXM) and Stress and Deformation over Time (SDOT) interdisciplinary working groups to answer the basic earthquake science question of “How are faults loaded across temporal and spatial scales?” by constraining how absolute stress and stressing rate vary laterally and with depth on faults, and by evaluating the time dependence of stress transfer on faults.
Broader Impacts This project has supported the training of one LSU graduate student and one UH graduate student to conduct research and gain valuable experience in computational modeling, critical thinking skills, and scientific communication. This research was presented at the 2020 SCEC Cajon Pass Earthquake Gate Workshop, the 2022 SCEC Annual Meeting, and several other subsequent presentations.
Exemplary Figure Figure 3.
Linked Publications

Add missing publication or edit citation shown. Enter the SCEC project ID to link publication.