2/3rds chance of a Loma Prieta+ class quake in 30 years

Mr. FoRK fork_list at hotmail.com
Tue Apr 22 22:09:09 PDT 2003


Hmm. Move to Seattle?

----- Original Message ----- 
From: "Rohit Khare" <khare at alumni.caltech.edu>
To: <fork at xent.com>
Cc: "Adam Rifkin" <a at xent.com>; "Smruti Vidwans" <smruti at itsa.ucsf.edu>
Sent: Tuesday, April 22, 2003 8:55 PM
Subject: 2/3rds chance of a Loma Prieta+ class quake in 30 years


> Still leaves me scratching my head as to whether I should buy quake 
> insurance or not. $5K of coverage with a $1K deductible is $150+/yr -- 
> more than renter's insurance to begin with.
> 
> I'm in a fairly modern apartment building, but I guess the whole point 
> is that I couldn't imagine anything happening to *my house*... :-)
> 
> Rohit
> 
> Quake scientists predict Big One likely by 2032
>          Bay Area fault study estimates 62% chance of deadly 6.7 temblor
> 
> David Perlman, Chronicle Science Editor
> Tuesday, April 22, 2003
> URL: http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2003/04/22/QUAKE.TMP
> 
> In the most detailed investigation ever made of earthquake hazards 
> throughout the Bay Area, scientists warned Monday that at least one 
> severely damaging and deadly quake is very likely here within less than 
> 30 years.
> 
> That warning came amid new scientific estimates of the danger levels 
> along the region's hazardous seismic faults.
> 
> According to the study, there is a 62 percent probability of a major 
> quake with a magnitude greater than 6.7 striking the region before the 
> year 2032.
> 
> There is a more than 80 percent likelihood that a smaller but still 
> very damaging temblor of magnitude 6 to 6.6 will strike here during 
> that time period, the scientists agreed.
> 
> Such a quake in the right place, with a magnitude of 6 or greater, 
> could be a total disaster, they said -- particularly if it struck along 
> a fault like the Hayward, which runs through the most densely populated 
> neighborhoods of the East Bay.
> 
> "In fact," said Mary Lou Zoback, former chief of the earthquake hazards 
> team at the U.S. Geological Survey in Menlo Park, "when you integrate 
> all the estimates over the entire region, a severely damaging quake 
> with a magnitude greater than 6 becomes a certainty."
> 
> For the first time, more than 100 earthquake experts at the U.S. 
> Geological Survey and other public and private agencies joined forces 
> this year for the study. They ran new computer programs based on new 
> seismic information to calculate losses in life and property that would 
> be caused by intense ground shaking from major temblors in the area.
> 
> Working with the federal agency's seismologists and geophysicists to 
> produce the new estimates have been other scientific teams at the 
> state's Office of Emergency Services, the California Geological Survey, 
> the Association of Bay Area Governments, and the Federal Emergency 
> Management Agency, as well as major universities and private earthquake 
> engineering firms.
> 
> The purpose of the interagency effort was to once again alert Bay Area 
> residents, builders and city officials that new seismic knowledge is 
> convincing scientists ever more strongly that somewhere in this 
> earth-shaking region a Big One is bound to strike, sooner or later, and 
> that only preparedness can minimize the devastation.
> 
> Less than four years ago, a smaller working group estimated that the 
> 30-year probability of a quake with a magnitude of 6.7 or greater 
> hitting "somewhere" in the Bay Area was 70 percent. And although the 
> new probability for a magnitude 6.7 quake is lowered to 62 percent, 
> that decrease doesn't mean the danger is lessened, said geophysicist 
> David P. Schwartz of the U.S. Geological Survey, who led the new 
> working group.
> 
> Estimates compiled by the group depend in varying ways on many factors, 
> Schwartz said. Among them are: how rapidly the slabs of the Earth's 
> crust are moving throughout the San Andreas Fault zone, where and how 
> rapidly some of the smaller faults are creeping in slow motion, and 
> even on how much -- if at all -- the abrupt motion of the great 1906 
> San Francisco quake provided long-term relief for some of the seismic 
> stresses that have been building up underground on the other Bay Area 
> faults for centuries.
> 
> "Our new data now is much more sophisticated and much more robust," 
> Schwartz said, "but our results must still reflect many uncertainties. 
> So we have to accept a broad error range, which could be anywhere from 
> 38 percent to 87 percent, considering many different earthquake 
> theories -- which poses a big uncertainty.
> 
> "What we do know for sure, however, is that any big earthquake in the 
> Bay Area will produce damaging ground motions over broad areas, and at 
> substantial distances from the source of the quake."
> 
> According to the new report, the most hazardous quake region in the Bay 
> Area now is the combined Rodgers Creek and Hayward fault systems, which 
> run from north of Santa Rosa to south of Fremont through some of the 
> area's most densely populated communities.
> 
> The 30-year probability of a large quake along that system alone is 
> estimated at 27 percent, and if one does occur on that system, the 
> danger from severe shaking is expected to extend westward beneath the 
> bay and cause widespread damage to structures built on soft soil along 
> the Peninsula and in the pre-1906 bay fill areas of San Francisco's 
> waterfront and downtown Financial District, the scientists warn.
> 
> Another endangered area lies along the western side of the San Andreas 
> Fault in San Mateo, Santa Cruz and Monterey counties. It's an area that 
> lies between the infamous San Andreas and the little-known offshore San 
> Gregorio Fault. Although the probability of a large quake on the San 
> Gregorio is only 10 percent, and on the San Andreas it is 21 percent, 
> the combined odds of a magnitude 6.7 quake striking either of them rise 
> to 34 percent within 30 years.
> 
> The last big earthquake to hit the San Francisco Bay Area was the Loma 
> Prieta temblor of 1989. Although it struck in the sparsely settled 
> Santa Cruz mountains with a magnitude of 6.9, it made 16,000 buildings 
> uninhabitable as far off as San Francisco and the East Bay. A similar 
> quake rupturing the entire Hayward Fault is likely to wipe out at least 
> 150,000 buildings, according to ABAG's current analyses.
> 
> With the report issued Monday, the earthquake working group also 
> produced a series of "shake maps" showing the intensity of ground 
> motion that would be induced by a large quake on any of 34 different 
> faults and fault segments in the region.
> 
> The maps and other information on the latest probability estimates for 
> all significant Bay Area faults are being posted today on a link to the 
> U.S. Geological Survey's earthquake site:  http://quake.usgs.gov/ 
> 
> 


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