Geologist's Research Predicts Large SoCal Earthquake
Posted: Wednesday, September 28, 2011
It's not unusual to find professor Nate Onderdonk and his students digging trenches in the dirt at the base of Southern California's San Jacinto Mountains, examining how the layers have been impacted by plate tectonics.
Onderdonk, 37, who teaches at California State University, Long Beach, is an expert when it comes to analyzing how landforms evolve through time and how faults change the landscape.
The professor received a $65,516 grant this year from the U.S. Geological Survey's Earthquake Hazards Fund to continue his research and study the fault history of the San Jacinto Fault Zone, which he said is one of the state's most seismically active areas and poses and threat to the Inland Empire.
Through his research, Onderdonk said he is looking for patterns with the hope that he might be able to predict the next big earthquake in Southern California, which he believes is due to happen anytime now.
"One of the main goals is to look for patterns — if there is a pattern, what is that pattern," he explained. "So far, we've been able to document the timing of the last seven large earthquakes (larger than a 6.5 on the Richter scale), large enough to break the earth's surface.
"The timing between these last seven earthquakes has always been between 160 and 200 years. And so on average, there should be one large earthquake every 180 years … We estimate the last major earthquake was around 1800, so that was about 200 years ago, and if this pattern is consistent then we should be expecting another large earthquake."
Although Onderdonk said the data isn't conclusive enough to estimate the next large earthquake down to the exact year, he said the research helps him guess what areas of the state might be most impacted in the next large earthquake.
"Most of this work can be used to estimate the amount of shaking that new buildings or bridges and power stations and things like that need to account for and what the probability of an earthquake is," he said. "This keeps us aware of the possibilities, and reminds us that earthquakes are a natural, inevitable cycle."
Even if a large earthquake, something greater than a 6.5 on the Richter scale, were to occur in Southern California, Onderdonk said many people who live in this area have misconceptions about what such an event would mean.
"People sometimes ask me if a large earthquake could cause part of California to break off and fall into the ocean," he said. "It's a myth — we are on a continent that is not floating, but solid rock all the way down. We could not be separated in one earthquake, although new waterways might be created."
Another misconception people have, Onderdonk said, is that fault lines resemble large cracks in the earth's surface. Actually, fault lines can be very difficult to see, and are not usually marked by large cracks — instead, researchers find fault lines by looking at rock or cliff formations have side-to-side formations, or rivers and streams with s-shaped curves.
"Most people have driven along a fault and not realized it," Onderdonk said. "It can take years to find just the right sediment and excavate trenches and have a cross-sectional view of a fault."
Onderdonk is presenting a free lecture, "Anticipating The Big One," at 6 p.m. on Thursday, Oct. 6, at the Pyramid Annex at CSULB.source
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