[MplsSteve]

Just so I understand this correctly...

The faults that are currently in Los Angeles County are off-shoots (or separate faults) of the San Andreas fault?

For example, the Northridge quake (was it in '93 or '94?) could have been from an off-shoot fault of the San Andreas fault - or from its own separate fault?

[ErnBatavia]

Northridge was an entirely separate fault, altho they're like cobwebs throughout the entire state so there could be some minor tie-in.

[Heyworth]

For example, the Northridge quake (was it in '93 or '94?) could have been from an off-shoot fault of the San Andreas fault - or from its own separate fault?

Basically an offshoot. The thing to understand is that the San Andreas is basically a north-south fault, from the top of the Sea of Cortez to San Francisco and then out to sea, and the general movement trend is that the plate with L.A. on it is moving north. But the fault's not straight, and from around Palm Springs to out near Bakersfield it trends as much east-west as north-south, grinding one plate against another head on along that stretch. This causes all sorts of fractures way deep down--thrust faults-- and it was one of those cracks slipping that caused the Northridge quake.

That was a scary night.

[markman46]

no,the San Andres is just the main north south fault, there are many small fault that criss cross all of SOCAL

[markman46]

Steve;

go here to see the faults

http://earthquake.usgs.gov/eqcenter/recenteqsus/Maps/US2/33.35.-118.-116.php