From the USGS – Updated:
http://earthquake.usgs.gov/earthquakes/eventpage/ci15481673#summary
Event Time
- 2014-03-29 04:09:42 UTC
- 2014-03-28 21:09:42 UTC-07:00 at epicenter
- 2014-03-28 21:09:42 UTC-07:00 system time
Location
33.919°N 117.944°W depth=7.5km (4.6mi)
Nearby Cities
- 1km (1mi) S of La Habra, California
- 4km (2mi) W of Brea, California
- 5km (3mi) NNW of Fullerton, California
- 6km (4mi) E of La Mirada, California
- 546km (339mi) W of Phoenix, Arizona
Tectonic Summary
A M5.1 earthquake occurred at 9:09PM on March 28, 2014, located 1 mile easy of La Habra, CA, or 4 miles north of Fullerton, CA. The event was felt widely throughout Orange, Los Angeles, Ventura, Riverside, and San Bernardino counties. It was preceded by two foreshocks, the larger of M3.6 at 8:03pm. The demonstration earthquake early warning system provided 4 second warning in Pasadena.
There have been 23 aftershocks as of 10:00PM on March 28, the largest of which was a M3.6 at 9:30PM, and was felt locally near the epicenter. The aftershock sequence may continue for several days to weeks, but will likely decay in frequency and magnitude as time goes by.
The maximum observed instrumental intensity was VII, recorded in the LA Habra and Brea areas, although the ShakeMap shows a wide area of maximum intensity of VI. The maximum reported intensity for the Did You Feel It? map was reported at VI in the epicentral area.
This sequence could be associated with the Puente Hills thrust (PHT). The PHT is a blind thrust fault that extends from this region to the north and west towards the City of Los Angeles. It caused the M5.9 1987 Oct. 1 Whittier Narrows earthquake.
Previously, the M5.4 2008 Chino Hills earthquake occurred in this region. It caused somewhat stronger shaking in Orange County and across the Los Angeles Basin.
The moment tensor shows oblique faulting, with a north dipping plane that approximately aligns with the Puente Hills thrust.
The demonstration earthquake early warning system provided 4 second warning in Pasadena.