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Mountain View Voice

News - March 18, 2011

Could it happen here?

Prepare for a quake, but don't worry about a tsunami, geologists say

by Nick Veronin

The massive 9.0 magnitude earthquake and ensuing tsunami that rocked Japan last week has people all over the Bay Area and California thinking about the next big one. Though experts from the United States Geological Survey said that residents of inland, bay-bordering cities such as Mountain View aren't at risk from a tsunami, the prospect of a major earthquake is very real.

"On the Peninsula, the fault we worry about the most is the San Andreas Fault," said Dr. Tom Holzer, an engineering geologist, who works out of the Menlo Park offices of the USGS. "That fault is the one we think can cause the largest magnitude earthquake in the Bay Area."

According to Holzer, geologists think that the San Andreas, at its most forceful, might produce a magnitude 8.0 temblor, lower than the recent quake in Japan. In sheer magnitude, Holzer said, an earthquake triggered by the motion of the San Andreas would likely produce less shaking. However, it would also be less violent because of the type and size of the fault.

The unnamed Japanese fault, Holzer said, is part of what is known as a "subduction zone" — an area where two tectonic plates meet and one is forced beneath the other.

The San Andreas, on the other hand, is a "strike-slip" fault, where two tectonic plates are moving parallel to each other.

In the case of both types of fault, the friction created by a major movement is what causes a quake. But the plates that recently moved off the eastern shore of Japan had about three times the surface area grinding against each other than the San Andreas would.

Nearby faults

Holzer said geologists believe the Hayward Fault, which runs up through the East Bay, is due for a significant event, which could register as high as 6.7 on the Richter scale. While damage from such a temblor on the Hayward Fault — which is also a strike-slip fault — would be "catastrophic" in the East Bay, damage to the Peninsula would likely be "moderate," Holzer said.

Two small faults, which could be described as wrinkles created by the San Andreas, run through parts of Mountain View. However, the Monte Vista fault isn't likely to shake very hard, Holzer said, and it doesn't appear to shake very often. The most significant damage from the Monte Vista fault would likely come from the ground beneath roads and buildings being offset, he added, not the shaking itself.

'Don't lose sleep'

While it is certain that a quake will eventually hit the Bay Area, another USGS scientist said, residents in inland, bay-bordering cities like Mountain View need not worry about a tsunami.

"I wouldn't want your readers to lose a lot of sleep over that," said Tom Brocher, director of the earthquake science center for the USGS. "The seismic hazards are what they need to worry about, rather than the tsunami."

Brocher, who is based in Menlo Park, said that the narrow opening of the bay, along with its shallow depth, means that it would be highly unlikely for tsunami waters to do much damage to inland areas in the Bay Area, even in cities like Mountain View that abut the bay.

Coastal cities are the most at risk from a tsunami, Brocher said. He also said that the Bay Area faults, such as the Hayward and San Andreas, aren't likely to cause a tsunami.

"In this part of California, the tsunami risk is mainly related to distant earthquakes," he said.

Large tsunamis are created by subduction zone faults, he said. When those faults experience a major shift, the earth can suddenly drop or rise rapidly. If that happens with an underwater fault, that water will be shoved with great force and may result in a tsunami.

To illustrate his point, Brocher said that the massive 1906 earthquake, that razed much of San Francisco, only generated a swell of about 4 inches.

However, he said, that doesn't mean Mountain View residents shouldn't worry about the damage caused by a strong temblor.

Building codes

Modern California building codes mean that most Bay Area homes built after the 1970s are fairly safe, Holzer said — even when coming up against a quake like the one in Japan.

"Believe it or not, you could design to withstand that," he said, comparing buildings that comply with earthquake code to rubber bands. "Think of the tremendous stretching you can get with a rubber band. What you've got to do is design a building with those kinds of properties, so it's able to recover when the ground shaking causes it to sway back and forth."

Such properties have been built into the new El Camino Hospital building, according to Ken King, chief administrative services officer for the hospital.

He said the hospital is designed to remain functional even after a major quake.

The foundation of the hospital extends 9 feet down into the ground below it, and the massive columns that support the structure — weighing roughly one ton for every foot — are embedded 5 feet into the foundation. At its upper floors, the hospital's internal structure is designed to sway to absorb motion, King said. "Anything that moves within the building is designed to move without crashing into any other part of the building."

Pipes are designed to stay fully functional even if separate floors move at different rates and different directions during a temblor; backup power is designed to remain continuous, King said.

"We are one of the few hospitals in the state to be designed with the latest California building codes," King said.

Other dangers

A building's structural integrity is not the only thing one must consider when preparing for an earthquake, however, Holzer said.

"There is a big 'but,'" he said — "non-structural components."

Tall shelves, hanging lamps, plumbing and furniture are just a few things that could be damaged or cause damage. "All non-structural features, unless they're secured, those can be quite lethal in an earthquake," he said.

Ultimately, an individual or family disaster plan could make all the difference, said Jaime Garrett, public information officer for the Mountain View Fire Department.

For help devising such a plan, call the fire department at 903-6365, Garrett said.

The county offers AlertSCC.com, where residents can sign up for automated alerts on their telephones, cell phones and e-mail accounts. The Mountain View Fire Department also has Facebook and Twitter accounts, where emergency information would be posted.

In the event of an emergency, information would also be available on local radio and television — KFFH 87.9 FM and KMVP Channel 15.

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