Los Angeles’ Eastside shaken by 3rd earthquake in a month

LOS ANGELES — A magnitude 2.9 earthquake struck underneath the Los Angeles neighborhood of El Sereno on Monday morning, causing weak shaking throughout the Eastside and San Gabriel Valley.

The earthquake, which occurred at 5:07 a.m., was initially reported as a magnitude 3.2.

Communities that may have felt weak shaking include East Los Angeles, Alhambra, Monterey Park and South Pasadena, according to the U.S. Geological Survey. There were no immediate reports of damage.

The epicenter occurred just southeast of the intersection of Huntington Drive South and Edloft Avenue. It was two-fifths of a mile northwest from the epicenter of a magnitude 3.4 earthquake that rumbled on June 2, and about one-quarter of a mile west of a magnitude 2.8 earthquake that struck on June 4.

The earlier June earthquakes, also in El Sereno, were just beneath the plane of the Puente Hills thrust fault, a terrifying fault that has received far less attention than the San Andreas but is capable of generating catastrophic shaking.

A hypothetical magnitude 7.5 quake on the Puente Hills thrust fault — which runs under highly populated areas of L.A. and Orange counties — could kill 3,000 to 18,000 people, according to the USGS and Southern California Earthquake Center.

A rupture of a small portion of the Puente Hills fault caused the magnitude 5.9 Whittier Narrows earthquake, which occurred on Oct. 1, 1987, with an epicenter in Rosemead. That earthquake caused very strong shaking in areas close to the epicenter, which was included San Gabriel, Monterey Park, Montebello, Whittier, Pico River, Santa Fe Springs and Norwalk. The Puente Hills thrust fault was only discovered in 1999.

Eight deaths were reported from the Whittier Narrows earthquake and a major aftershock, which caused extensive damage in Whittier, especially in old and unretrofitted brick buildings where walls partially or completely collapsed, as well as a partial collapse of the two-story concrete May Company parking garage. The 1987 earthquake caused caused serious damage on the campus of Cal State L.A. and at the freeway interchange of interstates 5 and 605.

The 1987 earthquake also caused minor damage to Whittier High School. One brick building in Pasadena completely collapsed.

The Puente Hills thrust fault is like an angled ramp deep underground — deepest along the 210 Freeway corridor, where it is about 10 miles deep, and shallowest about a mile south of USC, where it is 2 miles under the surface.

The Puente Hills thrust fault is underneath a swath of communities across the region, including Pasadena; downtown L.A.; East L.A.; Whittier; large portions of the San Gabriel Valley, from Alhambra to Rowland Heights; and northern Orange County.

An average of five earthquakes with magnitudes between 3.0 and 4.0 occur per year in the greater Los Angeles area, according to a recent three-year data sample.

The earthquake occurred at a depth of 6.2 miles. Did you feel this earthquake? Consider reporting what you felt to the USGS.

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The first version of this story was automatically generated by Quakebot, a computer application that monitors the latest earthquakes detected by the USGS. A Times editor reviewed the post before it was published. If you’re interested in learning more about the system, visit our list of frequently asked questions .