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Was it an earthquake? Or just another NCAA Basketball bracket tumbling?
A moderate earthquake rattled La Habra, California at 9:09 p.m.–the first of several on Friday night, per the United States Geological Survey. A series of quakes, the first, a USGS measured 5.1 on the Richter scale centered in the town of La Habre, and a second, moments later, estimated at 3.4.
The giddy post-quake panic caused many Californians to jump onto social media sites, immediately figuring out first if it was real, and second, how strong and where was the epicenter?
The USGS reported: “A M5.1 earthquake occurred at 9:09pm on March 28, 2014, located 1 km (1 mile) east of La Habra, CA, 5 km (3 miles) north of Fullerton, CA and 33 km (21 miles) ESE of Los Angeles. The depth of the event is 7.5 km” below the surface.
According to the USGS web site, “The event was felt widely throughout Orange, Los Angeles, Ventura, Riverside, and San Bernardino counties. It was preceded by two foreshocks, a M3.6 at 8:03 p.m. and a M2.1 at 8:16 p.m. There have been 38 aftershocks as of 10:45 p.m., the largest of which was a M3.6 at 9:30 p.m., and was felt locally near the epicenter.”
Regarding how the public responded through the “Community Internet Intensity Map”–the USGS had this to say: “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.”
Most frequently asked questions include which fault line is associated with the quake. “This sequence could be associated with the Puente Hills thrust (PHT).” According to the USGS report. “The PHT is a blind thrust fault that extends from this region to the north and west towards the City of Los Angeles.” The fault can be attributed to causing the M5.9 1987 Oct. 1 Whittier Narrows earthquake.” Stated the USGS report. “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. In another report, the earthquake early warning system provided 4 second warning in Pasadena.
The La Habre quake was felt up and down the Southern California Pacific seaboard.