2/3rds chance of a Loma Prieta+ class quake in 30 years
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*... :-)
> 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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