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Evolution of the Stress Field in Southern California and Triggering of Moderate-Size Earthquakes: A 200-Year Prospective

Jishu Deng, & Lynn Sykes

Published May 10, 1997, SCEC Contribution #339

Changes in stress in southern California are modeled from 1812 to 2025 using as input (1) stress drops associated with six large (7.0 ≤ M < 7.5) to great (M ≥ 7.5) earthquakes through 1995 and (2) stress buildup associated with major faults with slip rates ≥ 3 mm/yr as constrained by geodetic, paleoseismic, and seismic measurements. Evolution of stress and the triggering of moderate to large earthquakes are treated in a tensorial rather than a scalar manner. We present snapshots of the cumulative Coulomb failure function (ΔCFF) as a function of time for faults of various strike, dip, and rake throughout southern California. We take ΔCFF to be zero everywhere just prior to the great shock of 1812. We find that about 95% of those well-located M ≥ 6 earthquakes whose mechanisms involve either strike-slip or reverse faulting are consistent with the Coulomb stress evolutionary model; that is, they occurred in areas of positive ΔCFF. The interaction between slow-moving faults and stresses generated by faster-moving faults significantly advanced the occurrence of the 1933 Long Beach and 1992 Landers events in their earthquake cycles. Coulomb stresses near major thrust faults of the western and central Transverse Ranges have been accumulating for a long time. Future great earthquakes along the San Andreas fault, especially if the San Bernardino and Coachella Valley segments rupture together, can trigger moderate to large earthquakes in the Transverse Ranges, as appears to have happened in the Santa Barbara earthquake that occurred 13 days after the great San Andreas shock of 1812. Maps of current ΔCFF provide additional guides to long-term earthquake prediction.

Deng, J., & Sykes, L. (1997). Evolution of the Stress Field in Southern California and Triggering of Moderate-Size Earthquakes: A 200-Year Prospective. Journal of Geophysical Research, 102(B5), 9859-9886. doi: 10.1029/96JB03897.