Scientists' paper revises downward chances of temblor on northernsegment
The northern Hayward Fault is less likely to experience a major quake
in the next three decades than previously thought, scientists said,
reaffirming a similar conclusion issued in late 1999.
Between now and 2030, there's only a 16 percent chance - less than one in
six - of another major quake on the northern segment of the Hayward Fault in the
East Bay, they say in an article published in Friday's issue of Science
By major quake, they mean one that's at least as bad as the 1994
Northridge quake in Southern California. That temblor killed 57 people and
caused $20 billion in damage.
That upholds a similar estimate in late 1999 by the U.S. Geological Survey
and other Bay Area geoscientists. Back then, they issued a so-called
"probabilities" report estimating the likelihood of a 6.7-magnitude quake in the
Bay Area by the year 2030. That report estimated a 16 percent chance of such a
quake on the northern segment of the Hayward Fault, which runs from Berkeley to
San Pablo Bay.
A decade earlier, the prospects looked somewhat worse for the northern
Hayward Fault. Back then, a 28 percent estimate was issued in a 1990 USGS
The Science article doesn't report fundamental new information, cautioned
seismologist Bill Ellsworth of the USGS office in Menlo Park. The article mainly
reports the same research data used in the 1999 forecast, albeit in more refined
fashion following "peer review" by outside experts, he says.
"It's bringing into print some of the information that was utilized by the
'Working Group '99,' " Ellsworth said in a phone interview.
In any case, lay people shouldn't take too literally the 12-point
difference between the 1990 and 1999 estimates. That's because the two
forecasts, issued almost a decade apart, were based on significantly different
data sets and assumptions.
For example, the 1990 report estimated the probability of another quake
like Loma Prieta, which occurred in 1989 and measured about 7.0 magnitude. By
contrast, the 1999 report used as its model a weaker quake, the 6.7-magnitude
Northridge shake of 1994.
Even so, "both of those (the 6.7 and 7.0 quakes) are very damaging
earthquakes," said Bob Nadeau, one of the co-authors of the Science article. The
lead author was UC-Berkeley geophysicist Roland Burgmann. CQ