A seismology study by scientists from Stanford and MIT, published in the journal Science on 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 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. 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. More