Sci­en­tists: If 8.2-mag­ni­tude earth­quake hit Cal­i­for­nia, dam­age would be cat­a­strophic

Pittsburgh Post-Gazette - - National - By Rong-Gong Lin II

Los An­ge­les Times

LOS AN­GE­LES — The earth­quake that rav­aged south­ern Mex­ico on Sept. 7 was the largest to shake the coun­try in nearly a cen­tury.

Like Cal­i­for­nia, Mex­ico is a seis­mi­cally ac­tive re­gion that has seen smaller quakes that have caused death and de­struc­tion. But the Sept. 7 tem­blor is a re­minder that even larger quakes — while rare — do oc­cur.

Sci­en­tists say it’s pos­si­ble for South­ern Cal­i­for­nia to be hit by a mag­ni­tude 8.2 earth­quake. Such a quake would be far more de­struc­tive to the Los An­ge­les area be­cause the San An­dreas Fault runs very close to and un­der­neath densely pop­u­lated ar­eas.

The dev­as­tat­ing quakes that hit Cal­i­for­nia over the last cen­tury were far smaller than the Sept. 7 tem­blor, which Mex­i­can author­i­ties set at mag­ni­tude 8.2 and the U.S. Ge­o­log­i­cal Sur­vey placed at 8.1. Mex­ico’s earth­quake pro­duced four times more en­ergy than the great 1906 San Fran­cisco earth­quake, a mag­ni­tude 7.8, which killed 3,000 peo­ple and sparked a fire that left much of the city in ru­ins.

South­ern Cal­i­for­nia’s most re­cent mega-quake was in 1857, also es­ti­mated to be mag­ni­tude 7.8, when the area was sparsely pop­u­lated.

A mag­ni­tude 8.2 earth­quake would rup­ture the San An­dreas Fault from the Sal­ton Sea — close to the Mex­i­can bor­der — all the way to Mon­terey County. The fault would rup­ture through coun­ties in­clud­ing Los An­ge­les, River­side and San Bernardino.

An 8.2 earth­quake would be far worse here be­cause the San An­dreas Fault runs right through ar­eas such as the Coachella Val­ley — home to Palm Springs — and the San Bernardino Val­ley, along with the San Gabriel Moun­tains north of Los An­ge­les. The fault is about 30 miles from down­town Los An­ge­les.

The earth­quake Sept. 7 oc­curred in the ocean off the Mex­i­can coast and be­gan about 450 miles from Mex­ico City — and it was rel­a­tively deep, start­ing about 43 miles un­der the sur­face.

In Mex­ico, “you’ve got (many) peo­ple a pretty long way aways from it,” seis­mol­o­gist Lucy Jones said Sept. 8. But in South­ern Cal­i­for­nia, “we’d have a lot of peo­ple right on top of it. It would be shal­low, and it runs through our back­yard.”

A mag­ni­tude 8.2 on the San An­dreas Fault would cause dam­age in ev­ery city in South­ern Cal­i­for­nia, Ms. Jones has said, from Palm Springs to San Luis Obispo.

South­ern Cal­i­for­nia would feel even worse shak­ing than what was ex­pe­ri­enced in Mex­ico. Mex­ico’s earth­quake struck un­der the ocean and was deep; “se­vere” shak­ing (des­ig­nated by the USGS as in­ten­sity level 8) struck only a rel­a­tively small part of the coun­try that hap­pened to be sparsely pop­u­lated.

In con­trast, the 6.7 earth­quake that struck Northridge in 1994 was smaller in mag­ni­tude and pro­duced less over­all en­ergy. But be­cause that earth­quake was ex­tremely shal­low — strik­ing be­tween just four and 12 miles un­der the sur­face — the in­ten­sity of shak­ing that hu­mans felt at the sur­face was far worse than what hit Mex­ico.

Peo­ple in the San Fer­nando Val­ley dur­ing the 1994 Northridge earth­quake felt “vi­o­lent” shak­ing, which the USGS clas­si­fies as in­ten­sity level 9.

A mag­ni­tude 7.8 earth­quake on the San An­dreas would pro­duce in­ten­sity level 10 shak­ing, which is per­ceived by hu­mans as “ex­treme,” ac­cord­ing to a USGS re­port pub­lished in 2008, called ShakeOut, that en­vi­sioned such a sce­nario. Ex­treme shak­ing would blan­ket huge swaths of South­ern Cal­i­for­nia — an earth­quake that no one alive to­day has ex­pe­ri­enced in this re­gion.

The ShakeOut sce­nario en­vi­sioned the earth­quake be­gin­ning to move the San An­dreas Fault at the Sal­ton Sea close to the Mex­i­can bor­der, then mov­ing rapidly to the north­west to­ward L.A. County.

Mex­ico City rode out the earth­quake Sept. 7 bet­ter than a dev­as­tat­ing 1985 tem­blor that killed thou­sands of peo­ple there, in large part be­cause the cap­i­tal was so far away from the epi­cen­ter of the quake two weeks ago. The cap­i­tal is about dou­ble the dis­tance from the epi­cen­ter Sept. 7 as it was from the earth­quake that struck 32 years ago.

The U.S. Ge­o­log­i­cal Sur­vey pub­lished a hy­po­thet­i­cal sce­nario of what a mag­ni­tude 7.8 earth­quake on the San An­dreas Fault would look like. The sce­nario is still a use­ful look to imag­ine what an 8.2 would do to much of South­ern Cal­i­for­nia. Both earth­quakes would bring gen­er­ally the same in­ten­sity of shak­ing to Los An­ge­les, but the 8.2 earth­quake would send more in­tense shak­ing to ar­eas far­ther north and west, such as Santa Bar­bara and San Luis Obispo.

Here’s what could hap­pen if it struck at 10 a.m. on a dry, calm Thurs­day in Novem­ber, based on an ear­lier in­ter­view with Ms. Jones and ac­cord­ing to the ShakeOut re­port:

The death toll could be one of the worst for a nat­u­ral dis­as­ter in U.S. his­tory: nearly 1,800, about the same num­ber of peo­ple killed in Hur­ri­cane Katrina.

More than 900 could die from fire; more than 400 from the col­lapse of vul­ner­a­ble steel-frame build­ings; more than 250 from other build­ing dam­age; and more than 150 from trans­porta­tion ac­ci­dents, such as car crashes due to stop­lights be­ing out or bro­ken bridges.

Los An­ge­les County could suf­fer the high­est death toll, more than 1,000; fol­lowed by Or­ange County, with more than 350 dead; San Bernardino County, with more than 250 dead; and River­side County, with more than 70 dead. Nearly 50,000 could be in­jured.

Main free­ways to Las Ve­gas and Phoenix that cross the San An­dreas Fault would be de­stroyed in this sce­nario; In­ter­state 10 crosses the fault in a dozen spots, and In­ter­state 15 would see the road­way sliced where it crosses the fault, with one part of the road­way shifted from the other by 15 feet, Ms. Jones said.

“Those free­ways cross the fault, and when the fault moves, they will be de­stroyed, pe­riod,” Ms. Jones said. “To be that earth­quake, it has to move that fault, and it has to break those roads.”

The aque­ducts that bring in 88 per­cent of Los An­ge­les’ wa­ter sup­ply and cross the San An­dreas Fault all could be dam­aged or de­stroyed, Ms. Jones said.

A big threat to life would be col­lapsed build­ings. As many as 900 un-retro­fit­ted brick build­ings close to the fault could come tum­bling down on oc­cu­pants, pedes­tri­ans on side­walks and even roads, crush­ing cars and buses in the mid­dle of the street.

Fifty brit­tle con­crete build­ings hous­ing 7,500 peo­ple could com­pletely or par­tially col­lapse. Five high-rise steel build­ings — of a type known to be seis­mi­cally vul­ner­a­ble — hold­ing 5,000 peo­ple could com­pletely col­lapse. Some 500,000 to 1 mil­lion peo­ple could be dis­placed from their homes, Ms. Jones said.

South­ern Cal­i­for­nia could be iso­lated for some time, with the re­gion sur­rounded by moun­tains and earth­quake faults. The Cajon Pass — the gap be­tween the San Gabriel and San Bernardino moun­tains through which In­ter­state 15 is built, and the main route to Las Ve­gas — is also home to the San An­dreas Fault and a po­ten­tially ex­plo­sive mix of pipe­lines car­ry­ing gaso­line and nat­u­ral gas, and over­head elec­tric­ity lines.

All it would take is for the fuel line to break and a spark to cre­ate an ex­plo­sion. “The ex­plo­sion re­sults in a crater,” the re­port says.

ShakeOut co-author Keith Porter, re­search pro­fes­sor at the Univer­sity of Colorado, Boul­der, warned in a 2011 study in the journal Earth­quake Spectra that un­der cer­tain con­di­tions, a mag­ni­tude 7.8 earth­quake could cre­ate such a sud­den in­ter­rup­tion of high-volt­age in­ter­state trans­mis­sion of elec­tric­ity that “po­ten­tially all of the west­ern U.S. could lose power.”

Power could be re­stored within hours in other states, the sce­nario said. But restor­ing power in South­ern Cal­i­for­nia could take sev­eral days.

There could be up to 100,000 land­slides, sci­en­tists say, based off how many land­slides have oc­curred in past mag­ni­tude 7.8 earth­quakes. “The re­ally big earth­quakes … are much more desta­bi­liz­ing to the hill­sides,” Ms. Jones said.

Thou­sands could be forced to evac­u­ate as fires spread across South­ern Cal­i­for­nia; 1,200 blazes could be too large to be con­trolled by a sin­gle fire en­gine com­pany, and fire­fight­ing ef­forts will be ham­pered by traf­fic grid­lock and a lack of wa­ter from bro­ken pipes. Su­per­fires could de­stroy hun­dreds of city blocks filled with dense clus­ters of wood­frame homes and apart­ments.

The death toll could mount as hun­dreds of peo­ple trapped in col­lapsed build­ings are un­able to be res­cued be­fore flames burn through. Pos­si­ble lo­ca­tions for the con­fla­gra­tions in­clude South Los An­ge­les, River­side, Santa Ana and San Bernardino.

“If the earth­quake hap­pens in weather like to­day or in a Santa Ana con­di­tion, the fires are go­ing to be­come much more cat­a­strophic. If it hap­pens dur­ing a real rainy time, we’re go­ing to have a lot more land­slides,” Ms. Jones said.

Sev­eral dams could be shaken so hard “that they would re­quire emer­gency evac­u­a­tion,” Ms. Jones said. Even dam­age to just a sin­gle dam above San Bernardino could force 30,000 peo­ple out of their homes, the ShakeOut re­port said.

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