California Real Estate & Earthquakes
Property hazards such as earthquakes, fire, floods, are inevitable in areas like California. Real estate is a susceptible vulnerability here make no mistake. One thing you can do is find out as much about buying a house in California as you can. If you are looking at a house close to a fault line, the damage could be severe. Property information in California is the next best thing you can do in avoiding the worst an earthquake can do. If you find a property outside the super vulnerable liquefaction zone, you might have much less damage to deal with!
During the next big quake, a phenomenon called liquefaction might cause buildings in low-lying areas of the Bay Area to partly sink, perhaps even below water level, while seemingly rigid steel-frame buildings could warp or fall over because of weak welds, two leading experts said Thursday at a conference on earthquakes in San Francisco.
As much as 75 percent of low-lying fill land in the East Bay -- e.g. the Berkeley waterfront and Oakland airport -- might undergo liquefaction during another 1906-type quake, said researcher Thomas Holzer of the U.S. Geological Survey. The area is highly developed and includes facilities such as hotels, marinas, airport land and numerous California businesses.
Liquefaction occurs when quake waves ripple through loose or compacted soils, like the sandy fill that was poured into the bay over the last century to create new land for property development. During liquefaction, water in the ground rises and the soil becomes looser. Any buildings on the soil then tilts or sinks up to several feet.
Many acres of bay fill have been created since the estimated 7.9-magnitude 1906 quake. Hence the existing fill has never experienced a quake that powerful, said Holzer, who conducted the liquefaction study with three U.S. Geological Survey colleagues.
"It's a pretty significant vulnerability" because 1906-style shaking could cause liquefaction in between 40 and 75 percent of East Bay fill, he said in his talk at the 100th anniversary Earthquake Conference in Moscone Center.
Even during 1989's Loma Prieta quake, when the shaking was far weaker than in 1906, about 14 percent of the East Bay fill liquefied. The same area is clearly quite vulnerable come another 1906-style temblor, Holzer said.
At the same session, Thomas Heaton of the California Institute of Technology discussed how he and two Cal Tech associates modeled quake impacts on six- and 20-story steel-frame buildings during quakes of magnitude between 6.5 and 7.2. (Loma Prieta was about 6.9.)
He displayed results of a computer simulation that showed how a steel-frame building, when shaken several feet out of its normal position, begins bending until it "is hopelessly overbalanced and on its way to oblivion."
The majority of tall, steel buildings in California were originally welded before the magnitude-6.7 Northridge quake of 1994, Heaton said. Although those welds were thought to be strong enough before that quake, inspectors realized afterward that quite a few of their steel welds had fractured.
In a much stronger quake, the results could be disastrous for some buildings -- not only steel frame buildings, which many people mistakenly assume are as safe as can be, but non-ductile concrete structures as well, Heaton told the Chronicle.
(Non-ductile concrete buildings are those built of concrete structurally reinforced with steel, but where the quantity of steel is too low to strengthen the building against the swaying movement generated during an earthquake.)
Heaton doesn't perceive "any serious talk of doing (anything to strengthen the welds) because it'll cost a lot. And owners of buildings certainly don't want to talk about it: It will scare people."
"If we don't talk about this," he said, "it's certainly not going to get solved. It might end up having tremendously tragic consequences."