Dr. David Bowman discusses the likelihood of an imminent Orange County Earthquake. Photo by Camille Terazo/Daily Titan Staff Writer

The likelihood that Orange County will experience a major earthquake in the next 30 years may have increased with the magnitude 7.2 earthquake on Easter Day centered near Mexicali, Mexico.

That was one of the findings presented by Cal State Fullerton associate geology professors David Bowman and Phil Armstrong at a talk Tuesday night at the Fullerton Public Library.

"Does that mean that we're gonna have an earthquake? I have no idea," Bowman said to the nearly 40 attendees. “It's just one more day in the life of a fault. This made it more likely but I don't know how much more likely."

Bowman said that while the quake increased the stress on some major faults near Orange County, it actually relaxed the stress on the San Andreas, the only fault in Southern California where a magnitude 7.9 quake can happen.

The presentation began with Armstrong describing the history of earthquakes in Baja, Mexico. He emphasized that earthquakes of this magnitude happen here about every 25 years and each occurrence moves the earth about 1.5 meters, so this quake follows the pattern.

"This turned out to have a very complex structure," Armstrong explained. "The main shock happened on the Borrego fault in the southeast but it propagated to the northwest where most of the surface rupturing occurred."

From there, the shock ripped into Southern California, dispersing motion across the faults further to the northwest. To date, there have been more than 1,500 aftershocks as result of what geologists now call the Easter Day quake.

Bowman and Armstrong participated in the initial field reconnaissance near Mexicali the weekend after the earthquake. What they discovered was a complex system of faults that led to an interesting damage heterogeneity.

Bowman described encountering crumbled houses, toppled church steeples and flattened roofs in the small town of Colonia La Puerta; yet homes were undamaged in Durango, just a couple miles away.

He believes there were actually two or three earthquakes that occurred. The first was a smaller earthquake, about a magnitude 6.5, on the Borrego Fault. After a 10-15 second pause, the rupture picked up on the Pescoderos and Laguna Salada faults, causing them to fall like Dominoes.

Bowman said this "compound earthquake" was the reason the shaking lasted so long and that Mexicali didn't get hit as hard.

"Had the rupture continued along this fault, the energy released would have really walloped Mexicali," Bowman said.

There was no significant damage or loss of life, because the earthquake was in the middle of nowhere, Bowman added, unlike Haiti, where the fault broke right through the most densely populated part of the city.

"With earthquakes, like real estate, it's all about location, location, location," he said.

He emphasized that, so far in 2010, there have been about 60 earthquakes with a magnitude of 6 or greater worldwide, which makes it a pretty routine year. He blames the 24/7 media coverage and the Internet for desensitizing the public to earthquakes.

"Now every time a truck drives by, they're like, oh, there's another one!" he chuckled.

As far as predicting the next big quake to hit Southern California, he said there is no real way for geologists to know.

"We do live in earthquake country," Bowman said. "It will happen. When you see a hill, it's a fault, so be prepared. All of them will have an earthquake at some point."

Yorba Linda resident Risa Baylis said she keeps at least a case of water in the house and she keeps her gas tank half full like Bowman recommended.

"I feel like I'm semi-prepared," she said. "I do try to keep some canned fruit in the house, as well as soups."