Earthquakes that rattled Disneyland occurred near major fault

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The 4.0 earthquake that rattled the Disneyland Resort’s red-carpet premiere of the new Cars Land attraction occurred near a major fault in Southern California that can produce a magnitude-7.0 temblor.

The 8:17 p.m. shaker occurred very near a section of the Whittier fault, which straddles the border of Los Angeles and Orange counties along the suburbs of Whittier, La Habra Heights, Hacienda Heights, Rowland Heights, Brea and Yorba Linda. Wednesday evening's quake occurred just 8 miles from Disneyland.

"The Whittier fault is capable of producing a magnitude-7 earthquake, so is of concern to many seismologists, as it lies directly under a large population center," according a report posted on the Southern California Seismic Network.

More research is needed to determine which fault triggered the quake, but the initial analysis suggests it did not happen on the Whittier fault directly, said Caltech seismologist Egill Hauksson.

The fear would be that a small quake on the Whittier Fault could trigger a larger quake. The Whittier fault is relatively long, and the longer the fault, the bigger an earthquake can be.

Wednesday's quake was relatively shallow, at a depth of about 6 miles. Deeper quakes, Hauksson said, like those 8 to 10 miles below the surface, are more worrisome, because "quite often, these larger earthquakes start at greater depth, and they break ... to the surface and then run along the fault," Hauksson said.
Scientists have not detected an earthquake on the Whittier fault in modern history. The magnitude 5.6 Whittier Narrows earthquake in 1987, which caused destructive damage and killed eight people and $358 million in damage, actually occurred on the underground Puente Hills thrust fault, which lies under downtown L.A., the southern San Gabriel Valley and southeast L.A. County.

The Chino Hills earthquake, a magnitude 5.4, issued a strong jolt throughout Southern California in the summer of 2008, but most areas remained unscathed. A magnitude 4.7 quake in Inglewood in May 2009 shattered windows near the epicenter and renewed worries about the dangerous Newport-Inglewood fault, which killed 115 people during a 1933 earthquake. Finally, the predawn Pico Rivera quake in 2010, a magnitude-4.4, rattled nerves but caused no structural damage.

Nine aftershocks followed the main shock Wednesday night. The latest, a 1.7 shaker, hit just north of Yorba Linda High School at 7:35 a.m.

“It was a jolt, and a little teeny shake, and I kept thinking more was coming, but it stopped,” said Claudia Welch, a secretary at Yorba Linda High School who lives nearby. The school reported no damage.

The U.S. Geological Survey reported light shaking from southeast L.A. County into northern Orange County and the Riverside area.

With Disney's California Adventure near the main shock, the celebrities, media and other invitation-only guests who had gathered for the final piece of the $1.1-billion expansion of the Anaheim park were briefly scared.

"Earthquake just happened in so cal, felt at #carsland preview" tweeted @FindingMickey. "#disneyland #JustGotScarier."

The #JustGotScarier hashtag on Twitter was a play on the #JustGotHappier phrase Disney had used to promote Cars Land, which opens to the public Friday.

Hauksson said the earthquake should still serve as a reminder that Californians live in earthquake country and need to be prepared for the Big One.
http://latimesblogs.latimes.com/lanow/2012/06/earthquake-disneyland-near-whittier-fault.html