2008 Chino Hills earthquake

Earthquake

The Chino Hills earthquake was caused by oblique-slip faulting, with components of both thrust and sinistral strike-slip displacement. Its epicenter was within 3 mi of Chino Hills and its hypocenter was c. 15.5 km deep. The main shock was reportedly felt as far south as San Diego, and Tijuana, Mexico, It was the strongest earthquake to occur in the greater Los Angeles area since the 1994 Northridge earthquake.

As reported by The Orange County Register, three microearthquakes, all less than magnitude 3.0, occurred in Anaheim Hills, 7 mi southwest of Chino Hills, two months before the Chino Hills earthquake. There was an unusually low amount of seismic activity in Southern California in the week prior to the quake. Between July 20 and 26, 2008, there were no earthquakes in Southern California exceeding magnitude 3.0, thus there was speculation that the wane in seismic activity was a precursor to a possible larger event.

Impact

The Chino Hills earthquake caused no deaths or significant damage due to the physical location of its epicenter. Most of the infrastructure in the Chino Hills area is relatively new and well suited to withstand a large quake. Unlike previous earthquakes in the region—such as the 1994 Northridge earthquake and the 1987 Whittier Narrows earthquake, which caused serious structural damage and fatalities—this quake caused only minor damage. However, the high volume of telephone use following the shock overloaded provider capacity and disrupted service into the afternoon.

Amusement rides at Disneyland, Six Flags Magic Mountain, Universal Studios Hollywood and Knott's Berry Farm were evacuated and temporarily shut down. Pipes on a Macy's department store in Westfield Topanga ruptured during the tremor flooding the store which closed for a couple of days in order to be repaired. A light fixture damaged by the shock started a small fire in the Westfield MainPlace Mall in Santa Ana; since the fire was in an empty movie theater, nobody was harmed.

A gap was reported on California State Route 91 near Anaheim Hills, c. 7 mi southwest of the epicenter, but the California Department of Transportation concluded that the gap did not pose a danger. A minor landslide near the freeway caused some traffic congestion, but structural damage was reported. California Department of Transportation replaced an expansion joint on an Interstate 5 truck overpass at the El Toro Y Interchange. The roof of Placentia's public library nearly collapsed; afterwards, the building was closed for repairs.

Electrical outages were reported in Chino, Chino Hills, Diamond Bar and Pomona. Over 2,000 people lost power after a fire broke out at a La Habra power station, but electricity was restored that afternoon. Minor injuries from falling ceiling tiles were reported at a medical clinic in Brea. The earthquake affected candidates who were in the first day of the three-day California Bar Exam in nearby Ontario and Los Angeles. The State Bar ultimately did not count that portion of the test for or against any attorney candidates.

Aftershocks

Approximately 100 minor aftershocks and one presumed foreshock were reported within two days after the earthquake, 27 of which occurred within an hour after the earthquake. Four aftershocks of at least magnitude 3.0 were reported—the first, nine minutes following the initial earthquake, was the largest at magnitude 3.8; Twenty-eight aftershocks of at least 2.0 were reported.

Response

There was speculation that the Chino Hills earthquake may have been a foreshock to a larger earthquake. The Southern California Seismic Network's Aftershock Probability Report, produced minutes after the event, stated that "Most likely, the recent mainshock will be the largest in the sequence. However, there is a small chance, c. 5–10%, of an earthquake equal to or larger than this mainshock in the next 7 days."

Geologists at the United States Geological Survey and Uniform California Earthquake Rupture Forecast suggest that an earthquake with a magnitude of 6.7 or larger will almost definitely occur somewhere in the state within the next 30 years. then-California Governor Arnold Schwarzenegger said: "This earthquake reminds us to be prepared. [...] We were very fortunate that there were no serious injuries or property damage." Additionally, registration for the Great Southern California ShakeOut, a regional earthquake drill scheduled to occur on November 13, 2008, increased significantly in the aftermath of the earthquake.

References

References

1. "M 5.4 – 5km S of Chino Hills, CA – Impact". United States Geological Survey.
2. Robbins, Gary. (July 31, 2007). "Little known Yorba Linda fault caused Tuesday's quake". [[The Orange County Register]].
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4. (July 29, 2008). "Minor damage from 5.4 quake shows California has learned its lessons". Los Angeles Times.
5. Steinhauer, Jennifer. (July 29, 2008). "Earthquake Rattles Southern California". The New York Times.
6. Robbins, Gary. (May 24, 2008). "Third microquake shakes Anaheim Hills". [[The Orange County Register]].
7. Robbins, Gary. "Southern California Quake Activity Continues Odd Down Turn". [[The Orange County Register]].
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11. Colker, David. (July 30, 2008). "Post-quake callers overload phone systems". Los Angeles Times.
12. (July 29, 2008). "What's closed, delayed after the quake". Los Angeles Times.
13. Fisher, Marla Jo. (July 29, 2008). "College earthquake updates". [[The Orange County Register]].
14. Irving, Doug. (July 29, 2008). "O.C. Quake roundup: Disney rides down, trains disrupted, small landslide reported". [[The Orange County Register]].
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16. (July 29, 2008). "5.4 quake strikes near Los Angeles". ABC News.
17. Irving, Doug. (July 29, 2008). "O.C. QUAKE ROUNDUP: Disney rides down, trains disrupted, small landslide reported". The Orange County Register.
18. (August 8, 2008). "Rattled by Quake During California Bar Exam, Some Test-Takers Cry Foul".
19. Pierson, David. (July 31, 2008). "Will Chino Hills earthquake shake L.A. out of complacency?". United States Geological Survey.
20. Maugh II, Thomas. (July 30, 2008). "Quake originated about eight miles under Chino Hills". Los Angeles Times.
21. "Earthquake List for Map Centered at 34°N, 118°W". United States Geological Survey.
22. Whitcomb, Dan. (July 30, 2008). "Earthquake jolts lucky Los Angeles". Los Angeles Times.
23. (July 29, 2008). "Aftershock Probability Report". [[Southern California Seismic Network]].
24. (April 15, 2008). "California Has More Than 99% Chance of a Big Earthquake WIthin 30 Years, Report Shows". United States Geological Survey.
25. "M 5.4 - 5km S of Chino Hills, CA". United States Geological Survey.
26. National Geophysical Data Center / World Data Service (NGDC/WDS). (1972). "Significant Earthquake Database". [[National Geophysical Data Center]], [[National Oceanic and Atmospheric Administration.