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Could it happen here?

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

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.

Comments

Posted by HoleInTheHead, a resident of Old Mountain View
on Mar 17, 2011 at 11:49 am

"Prepare for a quake, but don't worry about a tsunami..."
I take it the chances of tidal waves in M.V. are nil.


Posted by Just wondering, a resident of Blossom Valley
on Mar 17, 2011 at 2:28 pm

I thought the intensity was 8.9...just wondering.


Posted by vkmo, a resident of Cuesta Park
on Mar 17, 2011 at 2:31 pm

1989 earthquake in San Francisco was of magnitude 6.9 on Richter Scale. Japan's earthquake was of magnitude 8.9 (now upgraded to 9.0). Per Web Link. "For each whole number increase, the amount of energy is 31 times greater than the preceding whole number. Using the same Richter scale measurement, a 6.3 releases 31 times more energy than a 5.3 but 961 times more energy is released as compared to a 4.3."

That would make Japan's earthquake 961++ times the intensity of the 1989 earthquake here. Despite all the earthquake preparedness in Japan, most of its earthquake zone structures were washed off or damaged irreparably and tens of thousands of people are believed killed. Over $100 billion in damage.

What should be the strategy for personal safety and to prevent destruction of our homes? There are earthquake standards for homes, which should be made tougher. In addition, I feel in each home there should be a small helmet, hiker's backpack with bedding, emergency food rations, water, medications for each person. These should be placed strategically near the front door. In case of an earthquake, I have read - hide under furniture, get out of the house to open space (take the helmet, pre-packed hiker's backpack). Of course surviving a Tsunami would require a different defense. All this should be thought about. Personally, I think survival in a 9.0 earthquake is a matter of luck - no amount of preparedness will be foolproof.


Posted by Steve, a resident of Shoreline West
on Mar 17, 2011 at 3:36 pm

vkmo- thanks for the addition of useful information in your comment. Indeed, there is "no amount of preparedness" that will be foolproof under these circumstances. However, architecturally there are buildings such as geodesic domes and pyramidal structures that can provide considerable resilience to such earthquakes.

With regard to "tidal waves" (a more descriptive term), I think it may be a mistake to disregard the possible occurrence of a large "tidal wave" hitting the coast of California. However remote the possibility, a "tidal wave" could align in just the right way, such that it enters through the Golden Gate and wraps around the bay area; a small one from last week went right up both the Santa Cruz boat harbor and San Lorenzo River.


Posted by Seer, a resident of Cuesta Park
on Mar 17, 2011 at 6:45 pm

A "tidal wave" is not the same thing as a tsunami. The tidal wave is literally the result of a large tide, and does not have the ripple-like propagation of a tsunami, nor the maximum power that a tsunami can have, since it doesn't result from as violent a force. Tsunamis used to be called tidal waves, but apparently they have been clearly distinguished enough that nobody uses tidal wave anymore.

A tsunami entering the bay is heavily dissipated because of the relatively small opening into a much larger body of water. While the exact amount of dissipation is hard to predict, in the 9.4 earthquake in Alaska in 1964, the wave height at Richmond and Hunters' point was about half that at the Golden Gate, and at Alviso it was 1/10th that at the GG.


Posted by Steve, a resident of Shoreline West
on Mar 18, 2011 at 12:13 am

<one dictionary definition>

tidal wave
noun

an exceptionally large ocean wave, esp. one caused by an underwater earthquake or volcanic eruption (used as a nontechnical term for tsunami [the term currently in vogue]).

¥ figurative a widespread or overwhelming manifestation of an emotion or phenomenon : a tidal wave of


Posted by Know-It-All, a resident of Old Mountain View
on Mar 18, 2011 at 2:54 am

Etymologically, tsunami (津波 or 津浪) is Japanese for 津 + 波 or 浪. Both 波 or 浪 are pronounce "nami" meaning "wave." 津 is pronounced "tsu" meaning several things..."sea" among them. Literally, tsunami means "sea wave."


Posted by Sue Nahmi, a resident of Cuesta Park
on Mar 18, 2011 at 2:41 pm

The type of quakes Japan has are caused by one plate shoving under another(called a subduction fault). Our quakes are caused by plates slipping alongside one another.
We can get some good ones with our slip faults, but a subduction fault is capable of much stronger quakes, like the latest in Japan.


Posted by steven Nelson, a resident of Cuesta Park
on Mar 25, 2011 at 10:37 am

The City of Mountain View, through its cooperative agreement with the local school district, built a very nice emergency water storage facility + well + diesel pump station at Graham Middle School's field. The nice thing about such a facility- our piped-in water supply would be cut in a large earthquake - and this facility could operate without electric power to supply drinking water for months.
-keep your buckets ready-


Posted by Steve, a resident of Shoreline West
on Apr 1, 2011 at 3:31 pm

Architecturally there are buildings such as geodesic domes and pyramidal structures that can provide considerable resilience to such earthquakes. Better than geodesic domes are geodesic spheres such that half of the sphere is above ground and the other below. Such a structure could allow for a "basement" like level or other green ecologically sustainable technologies for processing waste etc. Above ground a good portion of the could be devoted to solar-cells for the transduction of sunlight into electricity. Also, such structures are resilient in earthquakes and potentially so in hurricanes and floods.


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