Geologist's Research Predicts Large SoCal Earthquake

—Photo courtesy Nate Onderdonk

IN THE TRENCHES. Professor Nate Onderdonk, wearing a cowboy hat, and students analyze patterns in layers of dirt at the San Jacinto Fault Zone.

Posted: Wednesday, September 28, 2011

By Ashleigh Oldland

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.

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The best forecasts for earthquakes are about 10 times more accurate than a random prediction, a new study by scientists in California finds. (Credit: iStockphoto/Michal Bryc)

Assessing California Earthquake Forecasts

ScienceDaily (Sep. 27, 2011) — Earthquake prediction remains an imperfect science, but the best forecasts are about 10 times more accurate than a random prediction, according to a study published Sept. 26 in the Proceedings of the National Academy of Sciences.

In the study, UC Davis researchers compare seven different earthquake forecasts (including their own) that were submitted to a competition organized by the Southern California Earthquake Center.

The findings should help researchers both develop better earthquake forecasts and improve their tools for assessing those forecasts, said Donald Turcotte, a distinguished professor of geology at UC Davis and co-author of the paper.

The center launched the competition in 2005 based on a previous forecast published by the UC Davis group in 2001. Teams were invited to forecast the probability of an earthquake of magnitude 4.95 or greater, from Jan. 1, 2006, to Dec. 31, 2010, in almost 8,000 grid squares covering California and bordering areas.

During this time, 31 earthquakes struck in 22 grid squares, with the largest being the magnitude 7.2 earthquake just south of the U.S.-Mexican border in April 2010. All seven forecasts showed some utility in forecasting the locations of likely earthquakes: The best forecasts were about 10 times better than a random forecast.

The forecast submitted by the UC Davis group was the most accurate in picking the locations of the earthquakes, correctly labeling 17 of 22 grids and giving the highest probability of an earthquake in eight of these 17. Using a different forecasting method, Agnes Helmstetter of UCLA and colleagues gave the highest average probability of an earthquake for all 22 affected grids, although it did less well at assigning a higher probability to grid squares where an earthquake occurred.

"Just as there are alternative ways to forecast earthquakes, there are also alternative ways to evaluate the success of the forecasts," Turcotte said, noting that other publications evaluating the forecasts are expected.

The UC Davis group includes professors John Rundle and Turcotte, postdoctoral researcher James Holliday, and graduate students Ya Ting Lee and Michael Sachs. Also contributing were Chien-Chih Chen, National Central University, Taiwan; Kristy Tiampo, University of Western Ontario; and Andrea Donnellan of the Jet Propulsion Laboratory, Pasadena.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Davis.

Journal Reference:

Y.-T. Lee, D. L. Turcotte, J. R. Holliday, M. K. Sachs, J. B. Rundle, C.-C. Chen, K. F. Tiampo. Results of the Regional Earthquake Likelihood Models (RELM) test of earthquake forecasts in California. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1113481108

University of California - Davis (2011, September 27). Assessing California earthquake forecasts. ScienceDaily. Retrieved September 29, 2011, from http://www.sciencedaily.com /releases/2011/09/110928110018.htm