Los Angeles is at risk of a major earthquake, but a new study suggests that the tremors from “the Big One” may not be as devastating as scientists initially feared.
New simulations of shaking from a magnitude 7.8 earthquake on the southern San Andreas Fault suggest that Los Angeles could experience 50% less ground shaking than previously predicted.
While this may be good news for the City of Angels, researchers say residents (and builders) shouldn’t let their guard down: Many questions remain about the damage a major earthquake would cause in the region.
“This is just one scenario,” said the study’s co-author. Ye TaeyangHe is a postdoctoral researcher at San Diego State University.
The study has not yet been peer-reviewed but is posted on a preprint site. ESS Open ArchiveThe study updates computer modeling first conducted during the 2008 Great Southern California Shakeout, a project designed to quantify the impact of a magnitude 7.8 earthquake on the South San Andreas Fault, which runs 30 miles (50 kilometers) east of downtown Los Angeles.
by California Earthquake CenterThe worst such earthquake is expected to kill 1,800 people, injure 50,000 and cause $200 billion in damages.
Shakeout predicted surprisingly dramatic seismic activity in downtown Los Angeles, Thomas Heaton“The idea of using the Earth’s atmosphere to create a continental shelf is to create a place where the ocean can coexist,” said Dr. Schneider, a professor emeritus of geophysics and mechanical and civil engineering at the California Institute of Technology who was not involved in the research.
“It caused quite a stir at the time, and some people in the field wondered if the simulations were adequate,” Heaton told Live Science. In particular, the simulations suggested that the basins around the city, from the San Gabriel Basin where Pasadena is located, to the Los Angeles Basin where Los Angeles is located, would act as so-called “waveguides,” directing seismic waves toward the city. But the basins are structurally complex, so it’s unclear whether they would be perfect waveguides, Heaton said.
The earthquake simulations used in Project ShakeOut weren’t as detailed as today’s technology allows, Ye told Live Science. For example, the models depicted the earth’s surface between the fault and Los Angeles as smooth. Ye and study co-author Kim Olsen, a seismologist at San Diego State University, used newer simulations that included actual topography as well as detailed information about the shape of the fault and how waves travel below the surface.
The survey improved Los Angeles’ outlook: “The ground motions are still intense, but not as dire as previously predicted,” Ye said.
The researchers found that while the basin around Los Angeles does guide some seismic waves, the mountainous terrain around the fault also has a scattering effect, so the waves entering the basin are not as strong as previously expected, and the waves leaving are not as strong either.
Still, that doesn’t mean Southern Californians can rest easy.
“It’s important that they actually redid this calculation, and I applaud them,” Heaton said. “That’s a good scientific advance. But what’s still missing from the whole analysis is actual data from the earthquakes.”
Heaton said the area is currently well-covered by earthquake monitoring networks, but more earthquakes need to occur to get data points.
Another consideration is that earthquake motions can vary widely even within the Los Angeles area, no matter what the average shaking across the city might be, he said. Zachary Ross“The idea is to create a geophysicist’s team, but we’re not sure what to do with that,” said David Schneider, a geophysicist at the California Institute of Technology who was not involved in the study.
The central part of the Los Angeles basin sits on sediment that is relatively loose and could move easily during an earthquake, while areas closer to the mountains may have harder, more resistant bedrock, Ross said. In addition to the San Andreas fault near Los Angeles, there are several other fault systems, each of which creates its own hazards.
“That’s part of what makes this whole problem so difficult,” Ross told Live Science. “At the end of the day, even if we can get this one simulation to be pretty plausible, it’s still just one simulation.”
