Seismic constraints and coulomb stress changes of a blind thrust fault system, 2: Northridge, California

All of the observed surface faulting is shallow, extending meters to tens of meters below the surface. Relocated aftershocks reveal no seismicity shallower than 2 km depth.

Although many of the aftershocks lie along the thrust fault and its up-dip extension, there are also a significant number of aftershocks in the core of the gentle anticline above the thrust, and elsewhere on the up-thrown block. These aftershocks may be associated with secondary ramp thrusts or flexural slip faults at a depth of 2-4 km. The geological structures typically associated with a blind thrust fault, such as anticlinal uplift and an associated syncline, are obscured and complicated by surface thrust faults associated with the San Fernando fault that overly the Northridge structures.