Western San Gabriel Mountains, CA

Stop #3:  1971 Sylmar earthquake (blind thrust faults):  Epicenter

The parking lot of the Sand Canyon Country Club golf course is as close as we can get to the epicenter of the 1971 San Fernando Earthquake (also called the Sylmar earthquake) without playing a round of golf.  Occurring at 6:01 am on February 9, 1971, the magnitude 6.6 earthquake was a wake-up call to Southern Californians.  The shallow focus earthquake ruptured a part of the San Fernando fault (thrust fault), whose fault plane extends south towards the San Fernando Valley (Wikipedia, 2018) (SCEDC, 2013). 

Damage was extensive, especially for structures built on the fault. That led to the Alquist-Priolo Special Studies Zone Act passed in 1972. The purpose of this act is to prohibit the location of most structures for human occupancy across the traces of active faults. Building codes were strengthened to minimize the impacts when faults rupture. The one problem is that some of these faults are what we call blind thrust faults (that is, we do not see a trace of the fault on the surface)