Evolution of the stress field in southern California and triggering of moderate-size earthquakes: A 200-year perspective

Changes in stress in southern California are modeled from 1812 to 2025 using as input (1) stress drops associated with six large (7.0 less than or equal to M < 7.5) to great (M greater than or equal to 7.5) earthquakes through 1995 and (2) stress buildup associated with major faults with slip rates greater than or equal to 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 (Delta CFF) as a function of time for faults of various strike, dip, and rake throughout southern California. We take Delta CFF to be zero everywhere just prior to the great shock of 1812. We find that about 95% of those well-located M greater than or equal to 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 Delta CFF. 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 Delta CFF provide additional guides to long-term earthquake prediction.