US Geological Survey downgraded Friday’s 5.1 earthquake’s intensity as 7.5 km depth. The epicenter of the quake that jolted LA at 9:09pm on March 28, 2014, was located 1 km east of La Habra, California, 5 km (3 miles) north of Fullerton, CA and 33 km (21 miles) ESE of Los Angeles.
The event was felt widely throughout Orange, Los Angeles, Ventura, Riverside, and San Bernardino counties and was preceded by two foreshocks of M3.6 at 8:03pm and another M2.1 at 8:16 pm, said USGS in a statement.
There have been 38 aftershocks as of 10:45pm, 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 Community Internet Intensity Map (Did You Feel It?) was reported at VI in the epicentral area.
This sequence could be associated with the Puente Hills thrust (PHT), a blind thrust fault that extends from this region to the north and west towards the City of Los Angeles. It caused the 5.9 magnitude earthquake on Oct.1, 1987 known as the Whittier Narrows earthquake.
Prior to that, 5.4 magnitude earthquake in 2008 Chino Hills occurred in the same region and caused stronger shake in Orange County and across the Los Angeles Basin.