New supercomputer simulations show that a rupture on the San Andreas fault will cause minutes of severe “roller coaster” shaking in the Los Angeles Basin.

Researchers at the Southern California Earthquake Center simulated two scenarios: a northeast to southwest “zipper” rupture, and the reverse. It is said to be “the biggest and most detailed simulation of this region to date,” and the results mean that the San Andreas fault — recently pushed into the background by concerns over faults directly under the greater Los Angeles area — should still be a major concern.

The model shows that a northwest – running rupture along the San Andreas will send waves from San Bernardino along the base of the San Bernardino and San Gabriel Mountains and into the LA Basin, where sedimentary soil will amplify the distant quake. In earthquake-speak:

New simulations show that the chain of sedimentary basins between San Bernardino and downtown Los Angeles form an effective waveguide that channels … waves along the southern edge of the San Bernardino and San Gabriel Mountains. Earthquake scenarios with northward rupture, in which the guided wave is efficiently excited, produce unusually high long-period ground motions over much of the greater Los Angeles region, including intense, localized amplitude modulations arising from variations in waveguide cross-section. (source: Geophysical Research Letters)

The visualizations show you what they mean. Note how some of the most intense (red) vertical shaking from a quake starting near Palm Springs occurs in LA proper:

(Peak ground velocity for a rupture traveling southeast to northwest, funneling waves into the LA Basin. You can click on this image for a larger version. Source: Southern California Earthquake Center)

If you’ve got the bandwidth to grab a 30mb video, look at this animation of one of the simulations. The headline version — you really don’t want to be near downtown:

(You can click on this image for a larger version. Source: San Diego Supercomputer Center)

The southern San Andreas last ruptured in 1690.

The AP reported this story Saturday. So far, nothing in the Los Angeles Basin’s newspaper of record.

Oh, and don’t forget the tsunami that could threaten 1m people and cause $42b or more of damage …*

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Resources:
Southern California Earthquake Center
San Diego Supercomputer Center press release and project page

* … and for which there are still no innundation maps: not at the state’s Office of Emergency Services, NOAA, or even USC’s Tsunami Research Center.

Technorati Tags: California, Los Angeles, earthquake, Southern California

This entry was posted on Tuesday, May 16th, 2006 at 10:55 am by A Senior Administration Official and is filed under California Schemin'. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.