How it started: How it's going:

"Can't see the fault can ya, Russ?"
Would know there's a fault running through this person's front yard looking at it today? It's only been 50 years since the 1971 San Fernando earthquake deformed this lawn, severed the water pipes, & destroyed the block wall. #SanFernando71 2/

That's the problem & California lawmakers responded in 1972 w/ the Alquist-Priolo Earthquake Fault Zoning Act. This law regulates building construction across the active surface faults to mitigate damage from surface fault rupture. 3/

The #CaliforniaGeologicalSurvey evaluates active faults throughout the state, produces maps of surface fault traces, & establishes Zones of Required Investigation surrounding them. These faults exist throughout the greater Los Angeles area. @CalConservation #SanFernando71 4/

Faults have broken the surface in the LA area before, but 100 years of construction has masked the ground damage, so it takes a trained geologist to work thru different kinds of data to locate these active faults. #SanFernando71 #CaliforniaGeologicalSurvey @CalConservation 5/

Active surface faults run thru deserts & mountains, but the biggest concern is where they run thru cities & neighborhoods. Early in LA's history people didn't know to look for them, so they built everywhere. Eventually, some bldgs ended up directly on them. 6/