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Magnitude 4.7 Inglewood Earthquake, May 17, 2009

A magnitude 4.7 earthquake struck in Inglewood, California, about 3 miles east of Los Angeles International airport at 8:39 p.m. (PDT) local time, at a depth of 8.5 miles. Given that the location was in a densely populated part of the Los Angeles basin, it was widely felt. Updated estimates from the USGS ShakeMap and PAGER indicate that although strong shaking was experienced by many people, damage was light. Earthquake shaking was most pronounced in the heart of the Los Angeles basin, with strong shaking (MMI VI, capable of causing light damage) from city center south to Long Beach, and from the coast to Cerritos. The distribution of shaking in the region is shown on the ShakeMap (at right).

The focal mechanism is consistent with slip on the Newport-Inglewood fault, which was the source of the damaging 1933 M 6.4 Long Beach earthquake. Aftershocks, however, are west of the Newport-Inglewood fault trend rather than along it. The Los Angeles basin is crossed from northwest to southeast by the intensively studied Newport-Inglewood fault zone. In 1920, the Inglewood earthquake (M 4.9) occurred in nearly the identical location to this evening's earthquake. The 1920 event was the original reason for identification of this as an active fault zone capable of damaging earthquakes, which then later proved to be the case in the 1933 Long Beach event. After the 1933 event, the name of the fault zone was changed to the Newport-Inglewood fault zone in recognition that it is continuous from Beverly Hills to Newport Beach. At this point, the odds of a felt aftershock (M>3) are well below fifty-fifty, and will continue to diminish with time.

Over 40,000 responses have been received to "Did You Feel It" (DYFI) - please report your observations at the DYFI web site listed below. The Did You Feel It map shows an area of strong shaking (MMI=VI) in the vicinity of Compton, and light to moderate shaking (MMI=IV to V) over a broad area. The USGS PAGER results have been updated and the calculated number of people exposed to strong shaking is 890,000. Cities that experienced strong shaking (MMI=VI) include Cudahy, Torrance, Lynewood, Compton, West Compton, Gardena, East Compton, Willowbrook, Alondra Park, Lawndale, Lakewood, and South Gate. Over 3 million people are estimated to have experienced moderate shaking.

Links for additional information:

This map of historical seismicity, courtesy of Bob Dollar (USGS), shows the location of earthquakes from 1990-2005 in various colors. The recent magnitude 4.7 and two aftershocks are shown in orange. Traces of faults are shown as colored lines; the Newport-Inglewood fault zone is the set of orange lines from lower-middle right to upper center.

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