OSU professor shows link between San Andreas, Cascadia faults

Chris Goldfinger finds Oregon and northern California are overdue for major earthquake

By: Katy Weaver

Posted: 4/9/08

Although living on the West Coast means individuals don’t have to deal with hurricanes, blizzards or tornadoes, there is one natural disaster that people have to be ready for at a moment’s notice: earthquakes.

To many, earthquakes have been deemed the most unpredictable natural disaster of all.

However, new research done by Chris Goldfinger, an associate professor of marine geology at OSU, might allow scientists to better understand earthquakes and even predict when and where earthquakes will occur.

Goldfinger’s research is being published in the April issue of the Bulletin of Seismological Society of America.

The research was conducted with a team of geologists from the University of California, Berkeley and other universities across the country, and it focuses on studying the past to predict the future.

“Since we can’t predict [earthquakes], one of the tools we have to understand how faults work over time is to look at past earthquakes,” Goldfinger said.

Goldfinger’s work has focused specifically on two major fault lines on the west coast: the San Andreas Fault, which runs from the Gulf of California to Cape Mendicino, and the Cascadia subduction zone, which runs north from Cape Mendicino to British Columbia, according to the U.S. Geological Survey.

Goldfinger’s team studied the fault lines by observing underwater geological deposits from past earthquakes. Because the southern part of the San Andreas Fault is on land, the team conducted its research specifically on the northern San Andreas and southern Cascadia fault lines.

“Every time the Cascadia or San Andreas has a large earthquake, it triggers a submarine landslide along its whole length,” Goldfinger said. “So it’s fairly easy to go out with a ship to take core samples, find deposits and date the samples using radioactive carbon dating.

“This process gives us a time and place of past earthquakes for the last 10,000 years. If we do this in one spot, we can get a 10,000-year record from that spot, but if we do it along a whole fault line, we can tell how big the earthquake was and whether it ruptured along the whole length of the fault or just part of it.”

The team unearthed more than just random earthquake history though. Their data showed some striking similarities between the two fault lines.

“The earthquake records seem very similar in both places,” Goldfinger said. “[The two faults] are similar in 13 out of 15 of the last earthquakes, statistically showing that there is no difference in time, although there is a slight tendency for the Cascadia [fault] to go first.”

“We think that when Cascadia ruptures, it causes stress that transfers to the San Andreas, and we think that within a few decades this triggers the San Andreas to go off. Timing is not exact; it could be hours, it could be years or it could be decades, but it is pretty close in [geological] time either way.”

This fact that major fault systems have relationships with one another is a relatively recent discovery — only known for the last 15 years or so, according to Goldfinger.

“People used to think that fault lines were isolated from one another, but this doesn’t make sense anymore,” Goldfinger said. “Every piece of the earth is connected, so when one moves it is no longer surprising that the other pieces around it can be affected.”

But how can this new knowledge about the West Coast fault lines be utilized?

The research allows scientists to understand the directivity of the two fault lines. For example, San Francisco can be affected very differently by earthquakes depending on whether the fault ruptures from north to south or south to north.

When an earthquake hits the Bay Area and travels from south to north, it has a tendency to move out to sea and therefore cause significantly less damage. However, if the quake goes north to south, San Francisco will be severely shaken.

The research provided by Goldfinger’s team indicates that because the northern Cascadia fault triggers the southern San Andreas Fault, there is an increased likelihood that earthquakes will travel north to south, increasing damage.

Studying past earthquakes also gives scientists a geological timeline of when to expect the next one.

The last major earthquake occurring along the entire fault line, a 9 on the Ritcher scale, occurred in 1700.

According to Goldfinger, the northern part of the Cascadia fault has a major earthquake every 525 years. The southern part, however, has one every 278 years. Therefore, the southern part of the Cascadia fault is overdue for a major earthquake because it has been 308 years since the last one.

According to Goldfinger, earthquakes occurring in this area “Don’t often go past 300 years, so one is about due.”

“I’ve heard that an earthquake is overdue,” said Jeff Berwick, a freshman in biology. “It is supposed to happen any time now. It will definitely be interesting to see what happens when we do have one.”

Quick Facts

OSU professor Chris Goldfinger and his team conducted research on the history of earthquakes by examining underwater geological deposits in the southersn Cascadia subduction zone and the northern San Andreas Fault.

The last major earthquake in this region was 308 years ago

The northern Cascadia subduction zone ruptures on average every 525 years

The San Andreas Fault and Cascadia subduction zone have had earthquakes at the same geological time for the past 13 out of 15 quakes

Research has revealed earthquake history for specific faults from as long as 10,000 years ago

Katy Weaver, assistant news editor
news@dailybarometer.com, 737-2231