The huge dan­ger lurk­ing on the San An­dreas fault

Past ‘mega-quakes’ hint at dam­age an 8.2 could wreak

Los Angeles Times - - CALIFORNIA - By Rong-Gong Lin II

DESERT HOT SPRINGS, Calif. — As In­ter­state 10 snakes through the moun­tains and to­ward the golf cour­ses, hous­ing tracts and re­sorts of the Coachella Val­ley, it crosses the dusty slopes of the San Gor­gonio Pass.

The pass is best known for the spin­ning wind tur­bines that line it. But for ge­ol­o­gists, the nar­row desert canyon is some­thing of a ca­nary in the coal mine for what they ex­pect will be a ma­jor earth­quake com­ing from the San An­dreas fault.

The pass sits at a key ge­o­log­i­cal point, sep­a­rat­ing the low desert from the In­land Em­pire, and, be­yond that, the Los An­ge­les Basin.

Through it runs an es­sen­tial aqueduct that feeds South­ern Cal­i­for­nia wa­ter from the Colorado River as well as vi­tal trans­porta­tion links. It’s also the path for cru­cial power trans­mis­sion lines.

Cal­i­for­nia earth­quake ex­perts be­lieve what hap­pens at the San Gor­gonio Pass dur­ing a ma­jor rup­ture of the San An­dreas fault could have wide-rang­ing im­pli­ca­tions for the re­gion and be­yond.

They worry a huge quake could sever life­lines at the pass for weeks or months, cut­ting South­ern Cal­i­for­nia off from ma­jor high­way and rail routes as well as sources of power, oil and gas. South­ern Cal­i­for­nia’s cities are sur­rounded by moun­tains, mak­ing ac­cess through nar­row passes like the San Gor­gonio es­sen­tial.

Ex­perts have also ex­pressed grave con­cerns about the Ca­jon Pass, where In­ter­state 15 and key elec­tric and fuel lines run. Other prob­lem spots are the Te­jon Pass, through which In­ter­state 5 passes, and the Palm­dale area, through which the Cal­i­for­nia Aqueduct crosses.

One of the most dire sce­nar­ios ge­ol­o­gists have stud­ied is a quake that be­gins at the Sal­ton Sea. Such a quake would be par­tic­u­larly dan­ger­ous be­cause the fault’s shape di­rects shak­ing en­ergy to­ward Los An­ge­les.

South­ern Cal­i­for­nia has not seen an earth­quake like this since hu­mans started record­ing his­tory here. But the ge­o­log­i­cal ev­i­dence of such quakes is all around us.

In Desert Hot Springs, hints of the mighty San An­dreas fault lie all over: The rise of moun­tains that cre­ated the Coachella Val­ley. The oases and palm trees — made pos­si­ble only be­cause earth­quakes pul­ver­ized rocks that al­lowed springs to burst to the sur­face.

A ge­ol­o­gist’s trained eye can even spot ex­actly where

the fault is lo­cated. In one ex­posed cliff, Kate Scharer, a re­search ge­ol­o­gist with the United States Ge­o­log­i­cal Sur­vey, showed how one side of a hill has moved north­ward and sky­ward com­pared with the right side — and the gouge in the hill­side be­tween them was the fault.

Far­ther away, Scharer de­scribed how an old lower canyon was sev­ered from the up­per canyon and its an­cient source of wa­ter.

There’s a rea­son this par­tic­u­lar sce­nario vexes sci­en­tists:

An earth­quake ar­riv­ing from this di­rec­tion would point cat­a­clysmic shak­ing di­rectly into the heart of L.A., a kind of dis­as­ter that has not been seen since hu­mans be­gan record­ing his­tory in Cal­i­for­nia. Shak­ing could last for as long as three min­utes.

In a mag­ni­tude 8.2 sce­nario, the earth­quake would be­gin at the Sal­ton Sea, and then — like a big rig driv­ing on a free­way — speed up the San An­dreas fault to­ward Los An­ge­les County.

“It’s shoot­ing all of that en­ergy straight into the L.A. Basin,” Scharer said.

An earth­quake that be­gins more than 100 miles from L.A. might seem like some­thing you might not worry about.

But a mag­ni­tude 8.2 earth­quake is no or­di­nary earth­quake.

The tra­di­tional image of an earth­quake might be to show the epi­cen­ter — the point at which the earth­quake be­gins.

But that doesn’t tell the whole story. A bet­ter rep­re­sen­ta­tion of a large earth­quake would show how the earth­quake trav­els up the fault. And this be­comes more im­por­tant for large earth­quakes, which re­quire an in­cred­i­ble amount of area in which the sides of the fault move against each other.

So, ac­cord­ing to seis­mol­o­gist Lucy Jones, if a San An­dreas earth­quake be­gan at the Sal­ton Sea and ...

... ended at Mt. San Gor­gonio, it would be a 7.3 earth­quake.

.... stopped at the Ca­jon Pass, it would be a mag­ni­tude 7.6 or 7.7 seis­mic event.

...trav­eled up to Lake Hughes, the earth­quake would clock in at 7.8.

And “if it goes all the way from the Sal­ton Sea to near Paso Robles, we’d get an 8.2. So that’s prob­a­bly the big­gest we can have,” Jones said.

“I think it’s go­ing to go all the way to Paso Robles,” Jones said of the next Big One.

Jones cited a re­cent study by Scharer that found that earth­quakes hap­pen at the San An­dreas around the Grapevine on av­er­age ev­ery 100 years. It has been 160 years since the last ma­jor earth­quake on that sec­tion of the fault.

Here in the Coachella Val­ley and across the West Coast, sci­en­tists have been busy in­stalling new seis­mic equip­ment as they con­struct an earth­quake early warn­ing sys­tem, which could give places like L.A. sec­onds — or even a minute or more — of warn­ing be­fore the shak­ing waves ar­rive from an earth­quake.

The project, how­ever, is in dan­ger of los­ing fund­ing. Pres­i­dent Trump’s pro­posed bud­get sug­gests end­ing fed­eral fund­ing for the early warn­ing sys­tem. South­ern Cal­i­for­nia’s elected officials in Congress have voiced sup­port for con­tin­u­ing fund­ing of the project.

Here are some more an­swers to ques­tions given by Jones and Scharer as they gave a tour to elected officials on a trip or­ga­nized by the South­ern Cal­i­for­nia Assn. of Gov­ern­ments:

Why are we so con­cerned about the San An­dreas fault, when other faults are closer to cities?

The worst thing about an 8.2 on the San An­dreas is that all of South­ern Cal­i­for­nia would be hit hard at the same time. San Bernardino, for in­stance, wouldn’t be able to call for help from Los An­ge­les, which would have its own prob­lems.

“With 300 miles of fault all go­ing in the same earth­quake, you then have ev­ery­body af­fected at the same time,” Jones said. “The San An­dreas is the one that will pro­duce the earth­quake that’s go­ing to cause dam­age in ev­ery city” in South­ern Cal­i­for­nia — in­clud­ing Santa Bar­bara and San Diego.

Why is the San An­dreas con­sid­ered so likely to rup­ture?

Be­cause it’s Cal­i­for­nia’s fastest-mov­ing fault.

“It’s a lit­tle bit like ... the mo­ron who is driv­ing the fastest is the most likely to get into an ac­ci­dent,” Scharer said.

If a cou­ple were hold­ing hands across the San An­dreas fault, what would hap­pen when the earth­quake hit?

Here in Desert Hot Springs, the cou­ple would be thrown down. The ground would crum­ble. And in a mat­ter of sec­onds the two would be sep­a­rated by as much as 30 feet, Scharer said, al­most the en­tire length of a city bus.

One would lurch to­ward San Fran­cisco, and the other to­ward the Mex­i­can bor­der.

Can the San An­dreas trig­ger af­ter­shocks on other faults closer to the city?

Yes. One sce­nario of a San An­dreas earth­quake re­sults in af­ter­shocks on the New­port-In­gle­wood fault, which runs be­tween L.A.’s West­side through Or­ange County, and the Sierra Madre fault in the San Gabriel Val­ley. “We even had one in Sacramento,” Jones said.

Even the Hayward fault in the San Fran­cisco Bay Area could be set off by an earth­quake on the south­ern San An­dreas fault, Jones said. This has hap­pened be­fore. The great 1906 San Fran­cisco earth­quake, es­ti­mated at be­ing mag­ni­tude 7.7 to 7.9, sent a 5.5 af­ter­shock to Santa Mon­ica Bay and a mag­ni­tude 6 earth­quake to Im­pe­rial County, near the Mex­i­can bor­der.

Can you ex­plain how the San An­dreas fault works?

Western Cal­i­for­nia — San Diego, Los An­ge­les, Santa Bar­bara — is mov­ing to the north­west. Ar­eas to the east of the fault are mov­ing to the south­east.

How fast has the San An­dreas fault moved in the last mil­lion years?

It has moved about 22 miles in the last mil­lion years, Jones said.

When will the Big One hit?

We just don’t know. “Things don’t hap­pen like clock­work,” Scharer said.

The San An­dreas fault does not slice un­der the city of Los An­ge­les. So why should An­ge­lenos worry?

Los An­ge­les sits on a basin filled with sand and gravel.

So when shak­ing waves come, they “bang up against the side of the moun­tains and re­ver­ber­ate back out across the basin,” Scharer said. “Those waves are very ef­fec­tive at trav­el­ing through piles of gravel.”

Can sci­en­tists de­velop some­thing that could ab­sorb all the shak­ing en­ergy from a mas­sive earth­quake be­fore the city is hit?

No. The en­ergy pro­duced by a large San An­dreas earth­quake is “like the size of a small nu­clear bomb,” Scharer said.

The bomb dropped on Hiroshima pro­duced enough en­ergy to be equiv­a­lent to a mag­ni­tude 6 earth­quake.

Do small earth­quakes re­lieve pres­sure on the faults?

No. “Lit­tle earth­quakes don’t get rid of big ones,” Jones said. “The more lit­tle earth­quakes you have, the more you have to have big­ger ones.”

How should cities cope with the earth­quake risk?

Jones said util­i­ties, such as wa­ter, elec­tric­ity and gas, re­quire more at­ten­tion. “If we don’t deal with util­i­ties … we aren’t go­ing to be able [to] stay here and work,” she said.

Are Cal­i­for­nia’s build­ing codes equipped to deal with big earth­quakes?

A few Cal­i­for­nia cities have boosted safety reg­u­la­tions for older build­ings in re­sponse to earth­quakes. In re­cent years, sev­eral cities, in­clud­ing Los An­ge­les and San Fran­cisco, be­gan re­quir­ing retrofits of vul­ner­a­ble apart­ment build­ings. L.A. is even re­quir­ing retrofits of brit­tle con­crete build­ings.

But Jones is crit­i­cal of min­i­mum build­ing stan­dards for new con­struc­tion in Cal­i­for­nia, which she said al­low for a 10% chance of new build­ings col­laps­ing and killing peo­ple in an earth­quake.

Jones fa­vors in­creas­ing stan­dards for new con­struc­tion, or­der­ing build­ings de­signed so that they can be im­me­di­ately oc­cu­pied af­ter an earth­quake. She said that would in­crease costs by 1%.

“I think you need to be safe enough to walk into a build­ing, so that you don’t lose the use of it — and so your neigh­bors don’t lose the use of their build­ings,” she said.

Are new build­ings built bet­ter else­where?

Jones says new build­ings are stronger, for ex­am­ple, in Chile. That’s be­cause the coun­try makes those who build new build­ings re­spon­si­ble if the struc­ture suf­fers quake dam­age in the first decade af­ter it is com­pleted.

As a re­sult, own­ers have in­sisted on strong con­struc­tion, Jones said. And the coun­try rode out a re­cent 8.8 earth­quake well.

Pho­to­graphs by Allen J. Sch­aben Los An­ge­les Times

KATE SCHARER, a ge­ol­o­gist with the U.S. Ge­o­log­i­cal Sur­vey, walks along the San An­dreas fault in Palm Springs. The en­ergy pro­duced by a large San An­dreas quake is “like the size of a small nu­clear bomb,” she said.

ARIS ASPIOTES, a USGS field en­gi­neer, shows an earth­quake sen­sor at a seis­mic sta­tion in In­dio, Calif.

Allen J. Sch­aben Los An­ge­les Times

SEIS­MOL­O­GIST Lucy Jones, cen­ter, ex­plains to pol­i­cy­mak­ers how en­ergy from a large quake would travel up the San An­dreas fault. The fault, she said, could pro­duce a quake “that’s go­ing to cause dam­age in ev­ery city” in the South­land, in­clud­ing Santa Bar­bara and San Diego.

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