SCSN Caltech/USGS Preliminary Report Mw4.2 near Castaic Lake
Updated magnitude is Mw4.2 & location is 14 km N of Castaic or 14 miles NNW of Saugus, CA. This event is located halfway between the San Andreas fault and the less active San Gabriel fault.
The epicenter is near Clearwater Fault which is located adjacent to the communities of Lake Hughes and Leona Valley. The thrust faulting focal mechanism with a northeast strike is consistent with the motion on this fault.
The mainshock was preceded by foreshocks:
M Date time lat lon depth - km
3.1 2014/12/30 22:27:41 34 36.6 N 118 38.1 W 9.0 -- first foreshock M3
3.0 2015/01/03 18:58:10 34 37.0 N 118 37.9 W 2.0 -- 2nd foreshock M3
4.2 2015/01/03 19:18:09 34 37.2 N 118 37.8 W 8.9 -- Mainshock M4.2
The mainshock was ollowed by 31 aftershocks by 7 am Jan. 5. Biggest aftershock M2.5
Did-you-feel-it showed 2824 felt reports by 7 am Jan 5, from Ventura to Lancaster, and Long Beach to Bakersfield.
Small earthquakes are common in this region with 45 small quakes in 2014 and 17 earthquakes so far in 2015. Given this past history, this sequence may not be over yet but much bigger events centered in this region are unlikely or they would be a separate earthquake sequence.
In 2014 we had eight earthquakes of M4.2 or larger in southern California. This event occurred close to populated areas, and thus was widely felt.
Because the epicenter is in a remote area of the Transverse Ranges, there are no reports of damage so far.