‘The Big One’ Earthquake Will Hit L.A. Harder Than We Thought, Scientists Say

Simulation of a magnitude-7 quake on the San Andreas Fault. Seismic waves radiate outward, then deep into L.A. - STANFORD UNIVERSITYLA Weekly – by Gracie Zheng

A  seismology study by scientists from Stanford and MIT, published in the journal Scienceon Friday, finds that if the Big One hits the San Andreas Fault near Palm Springs, some seismic waves will travel near the path of the 10 Freeway into the heart of Los Angeles, where the city and its suburbs will suffer stronger ground motions than previously believed. Downtown L.A. will endure three times the shaking of surrounding areas, scientists now say.   

The study shows that a “funneling action” of seismic waves will roll straight into the Los Angeles Basin through a 60-mile-long corridor, striking a 13-million population region that stretches from the Santa Monica Mountains to Newport Bay and inland to the basins of the San Gabriel and Santa Ana rivers. The study confirms a 2006 supercomputer simulation that predicted L.A. could endure worse shaking than long feared. Greg Beroza, a professor at School of Earth Sciences of Stanford University who led the study, explains (See VIDEO below):

The waves travel through that corridor towards Los Angeles, essentially guided into the sedimentary basin that underlies Los Angeles. Once they’re in that basin, they reverberate; they get amplified. They cause stronger shaking than would otherwise occur.

(Video credit: Stanford University)

Stanford-MIT scientists devised a detailed new computer simulation using data from “omnipresent” waves that continually vibrate beneath Southern California. What they found is not good news for cities that sit atop the vast “sedimentary” L.A. Basin –  a huge rock bowl filled with eons of accumulated sand and sediment whose rim is made up of the San Gabriel, Santa Monica and Santa Ana Mountains, the Hollywood Hills and Palos Verdes Peninsula. Says Beroza:

“Our study indicates that high rises in downtown Los Angeles will get more strongly shaken by future earthquakes on the San Andreas Fault because of the wave-guide and basin effects that funnel waves from the San Andreas Fault into the Los Angeles Basin where the waves are trapped and amplified. What this means is that the threat posed by earthquakes to Los Angeles is higher than it would be otherwise because those earthquakes will shake Los Angeles more strongly.”

At their deepest point, the L.A. Basin sediments reach more than 30,000 feet into the earth, where they hit solid rock. Mount Everest, positioned upside down, could fit into this bowl.

“Those sediments are not compacted, like sand on the beach,” says Marine Denolle, first author of the study, who recently received her PhD in geophysics from Stanford. “They’re very compliant. So they can move very easily.

The study says:

Our ground motion predictions show strong seismic amplification in the Los Angeles sedimentary basin compared to surrounding areas…[W]e find seismic amplification in downtown Los Angeles with peak amplitudes up to three times larger than in surrounding areas.

Palos Verdes Peninsula and the Los Angeles Basin, with the San Gabriel Mountains in the distance. - DOC SEARLS/FLICKR

  • Doc Searls/Flickr
  • Palos Verdes Peninsula and the Los Angeles Basin, with the San Gabriel Mountains in the distance.

The study used “virtual earthquakes” to predict ground motion. Scientists used data taken of weak vibrations beneath the ground – which are actually generated by the movement of ocean waves and then transmitted into the earth – to construct a major, fake earthquake, according to Denolle.

“Those waves [are] transferred to the sea bottom. These get transmitted to the crust where we actually have instruments recording,” says Denolle.

Weak ground vibrations, known as “the ambient seismic field” in geology, are present all the time, but they’re so mild that they’re unnoticeable. Scientists have known about the ambient seismic field for more than 100 years, but viewed them as interference in their efforts to study earthquakes. Now, with this study, scientists made use of them – as proxies for strong seismic waves created by a big earthquake.

See also: The First 15 Minutes After the Big One

Beroza explains, “Even though billions of times weaker than earthquake waves, they interact with the complex geological structure of the crust just the same way.”

In the study, the scientists considered 96 simulated ruptures, or “examples of 96 possible earthquake sources” by selecting  different epicenters and rupture speeds on a 40-mile segment of the San Andreas Fault from roughly the junction of 10 Freeway and Highway 111 on the north (San Gorgonio Pass) to where the 10 crosses the fault on the south near Coachella.

Denolle explains in an email:

“We do not know which one actually would occur, so we account for different scenarios to look at an average of all possible scenarios.

“When you drop a rock in flat water, you can see circles moving outward on a growing circle. That’s exactly what seismic waves do, they move outward like this. Because the Earth is more complex than water, the circle is not perfect.”

Devices placed in the ground for four months along the fault in Palm Springs collected data from the ever-present ground vibrations.

Downtown L.A., in the background, will suffer movement three times that of surrounding areas. - LANA.JAPAN/FLICKR

  • lana.japan/Flickr
  • Downtown L.A., in the background, will suffer movement three times that of surrounding areas.

This study confirming the 2006 San Andreas simulation –  as well as reports of a new state geological map showing that the separate Hollywood Earthquake Fault runs directly beneath a new luxury complex and under Hollywood’s proposed  Millennium skyscrapers –  prompted one respected geologist to call for major changes at the Los Angeles Department of Building and Safety.

Robert H. Sydnor, an engineering geologist who worked for California Geological Survey for 25 years and is a life member of the Seismological Society of America, said via email:

Recent building permits and recent Environmental Impact Reports issued by the City of Los Angeles do not properly characterize the known problem of amplified earthquake ground-motion in Hollywood and downtown Los Angeles.

I have read 2013 official comments from the LA Planning Department that wrongly state that the earthquake ground-motion in Hollywood is no greater than elsewhere in the city. With the active Hollywood Fault cutting right through Hollywood, plus basin-edge amplification effects in strong-motion seismology, these LA City official comments are egregiously false and scientifically wrong.

It is time for a significant internal change within the Department of Building and Safety of the City of Los Angeles. Building permits for multimillion-dollar high-rise structures are being issued by LA City officials who have no understanding of strong-motion seismology, Holocene-active faults, and geologic hazards. This is a significant disservice in public safety.

Sydnor noted that studies on earthquake ground motion in Santa Monica and Los Angeles have been heavily published since the 1994 Northridge Earthquake, which killed 57 people and left more than 9,000 injured. 

Beroza leaves Angelenos with this thought:

“I should note that this [the San Andreas Fault] is not the only earthquake threat that Los Angeles faces. There are earthquake faults within Los Angeles that rupture in earthquakes less frequently than the San Andreas Fault, but when they do, they will shake Los Angeles very strongly.”

Follow Gracie Zheng on Twitter at @Gracie_Z. Follow LA Weekly News on Twitter at @laweeklynews.


25 thoughts on “‘The Big One’ Earthquake Will Hit L.A. Harder Than We Thought, Scientists Say

  1. My Fellow Americans:

    PFfftttt!!,… I’ve been to LA,… use to live just south of it for 6 years,.. what a shit-hole of foreign nationals, illegals,.. and commies in general.

    When the, “Big-One” hits,… and kills millions of those maggots,… I’m sure the headlines will read:


    JD – US Marines – There is a reason God had all the queers, fags, pedophiles, freaks, weirdos and commies move to California,.. especially the LA,.. and San Fran region,… its so he could wipe them out in one felled swoop! (San Fransico is actually located directly on top of the convergence point of three massive fault lines,…. who says God doesn’t have a sense of humor!!??)

    1. Can you point out in the bible where it says “kill them all and let god sort them out”??? Some christian you are!! So you lived in orange county or riverside for just 6 years and you know it all…BS There are aholes EVERYWHERE, and you help prove my point…

      1. Hi arf,

        Please allow me to state this carefully so you do NOT misunderstand my intent….:

        GO,…. FUK,….. YOURSELF!

        There,.. I think that is pretty clear,.. don’t you?

        No where did I mention the bible.

        No where did I state: “Kill them all…….”

        No where did I state I was a “Good” Christian.

        No where did I state that I am here to meet YOUR definition of what constitutes a “Good Christian”.

        No where did I say that there are NO decent people in LA, San Fran, California or any other part of the world for that matter.

        The only point proven here is: YOUR A F’n COMMUNIST! As proven by your trying to make statements on behalf that I NEVER stated or implied.

        Your ARE the typical kind of douchbag that feels others have to measure up to your definition of whatever your grip is.

        Why don’t crawl back under your commie rock,.. or go outside and finish putting the bumper stickers on your car that say:

        “I LOVE HILLARY FOR 2016”,…



        or anything along those lines would probably feel just right to you.

        Fuk off and die arf.

        JD – US Marines – The commies are coming out in force,.. and getting bolder by the minute.

        1. Awe geeze JD, HAHAHA, I haven`t seen you go off like that in a long time – if ever even. Damn that was a good ripp JD 😆 😎

        2. “If the officers are too strong and overbearing and the rank and file too passive, a result is decline”
          -page 65 The Art of War by Sun Tzu

          Pretty cool book, a friend of mine, who is a patriot and a warrior, sent it to me.

    2. The same could be said of parts the North East. But I don’t wish it on them.

      I sure hope no one posts an article about hurricanes hitting Gulf Coast. 😉

    3. It is pretty cruel to say that ALL people that live in an area are bad people. There are bad people EVERYWHERE, as there are GOOD people everywhere. Just because you lived somewhere for 6 years makes you no expert. I have lived all over the world, am I an expert? Hell no.

      I find you saying these things about people in California is mean and sick.

        1. We used to have a waterbed. That had to have been scary. I have been through a lot of Hurricanes, but never an earthquake. I pray if a big one does ever hit, the people will have some warning so they can leave. I don’t know if earthquakes come in strong or if there are small ones first. They are saying the Madrid fault line in the middle of the US is also waking up. Scary times!

          1. Quakes get your attention real fast…….just ask the cat. I hope you are doing okay where you are in the deep freeze. The New Madrid fault and the sink holes sounds like there is a problem developing in that area. I can’t imagine what would happen if that area does go-off…not good.

          2. Thanks, the weather is getting worse here, but so far not as bad as they said. The sinkhole is worrisome, but I feel we are far enough away, but my Cajun people that live down there, they I pray for! I think the BP oil spill was for them to get the Madrid started, that is why they drilled where they did. They want the Gulf Coast empty. But I ain’t leaving until God tells me too!!

          3. The bp situation is insane. I find it rather strange that Katrina and the bp oil disaster in that area is just some accident…..I just know that after 911, too many “accidents” have occurred that look like something else going on. Problem/solution seems to be in effect here. As for God, maybe what you are aware of is, in fact, his way of speaking to you??? I know it’s hard to just pick-up and leave….your awareness is probably your answer….don’t we always say,” I knew it.?”

          4. I agree ever since 9/11 things have picked up. As for moving, I have been praying for years to move, I really want to live in the country (rural). But I feel it God wanted us in the country doors would of opened, and we would be there. Believe me I have moved my feet in that direction, but still not in the country!! We even bought 12 acres on a dirt road, we did dirt work to level it, well in the winter the water will not drain. It is so heart breaking, but obviously we were not meant to live on that piece of land. I Love South Louisiana, for the most part people are friendly, the food is good and for now there are still jobs. I am from here and I have always been drawn back. I have left several times, but the spirit always pulled me back here!!

  2. NO S**T Shrelock!! If the san andres blows, and it will, all other faults will become active…Will have aftershocks on all faults for years…not to mention most of southern Ca’s water crosses the san andreas by way of aquaducts which will be messed up….

  3. Not much you can do except move or prepare. I remember the Feb 9, 1971 sylmar quake….6.1.. What I remember is that the cat ran up the wall to the ceiling…..that was the most amazing thing….Cats can really move in an earthquake.

    1. I was in bed in malibu and woke at 4am, the morning of the northridge eq…I layed there looking at the cieling thinking, why am I awake? I have to go to work in a couple hours…then I felt the “P” waves and knew what was about to happen…It shook, but not that bad, only had one thing fall over, but my dog slept right through it…My sisters place in lower santa monica was destroyed, flip here coffee table 180*…and I was closer to the EQ then her….Depends on the type ground you live on…

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