By Allie Mosier
For the Daily Titan

If you’ve ever taken a geology course the terms P-waves, S-waves, frequencies and the name San Andreas Fault probably sound familiar.

Dr. David Bowman, department chair of the geology department, held a seminar at the Fullerton Public Library on Oct. 8 to talk about the causes of earthquakes and earthquake preparedness.

The San Andreas Fault is the sliding boundary between the Pacific Plate and the North American Plate. In simpler terms, it is a crack in the ground that cuts through California.

Although Californians are no strangers to earthquakes, the San Andreas Fault is predicted to produce an earthquake of a magnitude of 7.8, which would cause severe damage.  The San Andreas Fault produces earthquakes approximately once every 150 years. Each time one occurs the fault moves 30 feet.

“The last earthquake that occurred on the southernmost part of the fault was over 430 years ago. That’s why we say it’s overdue,” said Bowman.

Although the San Andreas Fault is predicted to produce an earthquake of great magnitude, Bowman said the San Andreas Fault isn’t the biggest threat to California – the Puente Hills Thrust is.

The Puente Hills Thrust is a fault that runs from northern Orange County to downtown Los Angeles. It is predicted to produce an earthquake of a magnitude of 9.7.

Bowman estimated the earthquake would cause 7,600 fatalities, 12,000 injuries, 274,000 displaced households and a total economic loss of $130 billion.

“We’re right on the edge where severe damage occurs,” Bowman said. But he doesn’t believe this earthquake will occur in our lifetime.

Bowman has one simple formula to evaluate the risk of an earthquake: risk equals earthquake likelihood, plus likely shaking, plus building fragility.

“Buildings respond differently to different frequencies of shaking,” Bowman said.

Big buildings resonate to low frequencies and small buildings resonate to high frequencies.

An important factor that determines how a building will survive an earthquake is the material it is made out of. Buildings are usually made out of materials like adobe, unreinforced masonry, steel and wood.

Adobe has no strength in earthquakes and crumbles to nothing.

“This is why we see huge damages in earthquakes in the Middle East. The smallest earthquake can crumble (a building),” said Bowman.

Unreinforced Masonry, also known as brick, turns to dust when it is shaken. Bowman deems this as “dangerous building material.” Steel frame and wood frame buildings are both good for earthquakes because steel and wood can bend and flex.

“Buildings in California are made so they’ll survive an earthquake,” Bowman said.

Earthquake waves also determine the damage an earthquake produces. Body waves are the first group of waves and produce a high frequency motion. They are also strongest near the epicenter.

P-waves, or primary waves, are first to arrive but are weak. They produce a sound in the rock that you can’t hear but when they occur what you feel is a jolt. S-waves, or secondary waves, are second to arrive and produce a sharp, jolting, side-to-side motion. They are the most damaging waves.

Surface waves are the second group of waves to hit and produce a low frequency motion. Unlike body waves, they are strongest further from the epicenter. Two other types of waves are Love waves and Rayleigh waves. Love waves produce a swaying side-to-side motion and Rayleigh waves produce a rolling motion.

The size of the fault also determines the strength of an earthquake. Big faults, like the San Andreas, produce low frequency shaking. Small faults produce high frequency shaking and are most damaging to homes.

Soil types as well as the depth of basins determine the amplification of an earthquake. Loose, unconsolidated soil amplifies shaking from seismic waves.

“The more sand and gravel, the more shaking,” said Bowman.

In general, deeper basins have stronger amplifications. Bowman pointed out that the Orange County basin is only one mile to half-a-mile deep which would produce less shaking.

In order reduce damage caused by an earthquake, Bowman gave these simple recommendations: Don’t have objects above your bed and secure bookcases and televisions to the wall.

“The building isn’t the hazard, the contents of a building are the hazard,” Bowman said.

John Greenwood, a Fullerton resident attended the seminar because, “events like these are worth listening to,” he said.

“I came to see if I could find out anything new and to make sure I’m prepared,” said Kate Dalton, a Fullerton resident.

Because of the success of the shakeout drill that occurred last year, it is now mandatory statewide. The shakeout drill will occur every year on the third Thursday of October. This year it will take place on Oct. 15 at 10:15 a.m.

“Make it your disaster-prepared time,” said Bowman.