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Re: San Andreas Fault

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I don't want to start a flame war, but Methinks there may be some typos and
misunderstandings about the quoted story, based on sources here in the SF Bay
Area, that I consider reliable.  Here's the facts as I know them:

1)  The study are part of a review of earthquake risk in the Bay Area by the
Association of Bay Area Governments (ABAG) and the U.S. Geological Survey.

2)  The study is a preliminary damage scenario draft.  The final report is not
due for a year.

3)  Jeanne Perkins,  manager of ABAG earthquake preparedness decided to
release these preliminary conclusions because they were so startling different
from previous conclusions.  Lost in the hubbub about increased SF damage is
the increased risk from blind thrust faults in the San Jose area.  Read the
news stories linked below.

4)  The ABAG scenarios can be found at 
<A HREF="";></A>

5)  The uncertainty surrounding the science is excerpted below.  The ABAG
folks decided to err on the side of caution in pushing folks towards
preparation.  What We Want to Know 

This process of identifying fault segments is not an exact science;
professional judgment is involved, in part because little evidence of past
earthquake ruptures may be present. Scientists at USGS and other earthquake
researchers are reexamining the segments for use in future earthquake

For example, ABAG used the definition of the Peninsula segment of the San
Andreas fault identified in the 1990 report by the Working Group on California
Earthquake Probabilities (1990) (Ref. 17) in our On SHAKY Ground report (Ref.
1). The 1996 report by the Working Group on Northern California Earthquake
Potential (Ref. 16) changes the definition of some fault segments, including
the peninsula San Andreas, slightly. The length of this fault segment was
changed from 52 to 88 km; this longer fault segment (called the Peninsula-
Golden Gate San Andreas on the map which follows) extends north to outside the
Golden Gate, rather than stopping on the peninsula. It is unclear which of the
two versions of the San Andreas fault on the peninsula is the most likely to
rupture. However, the longer fault segment will result in an earthquake which
is much more serious than the shorter fault segment for both the City of San
Francisco and the entire Bay Area, as shown on the following pages. This fault
segment ranks behind the entire Hayward fault as having the potential to cause
the most damage in the Bay Area. Unfortunately, it is impossible as this time
to be completely certain which segment is "correct." 

What We Know and Don't Know 

The way in which faults are segmented is being rethought at the present time.
We anticipate that a major change in fault segment definitions will take place
by the fall of 1999 as a product of a new USGS working group.

6)  Work on Estimates of people killed or injured is just beginning according
to ABAG.  UCLA public health researchers are conducting this portion of the

7)  According to the USGS,  
<A HREF="";>,  </A>" ... the extent of the
1906 rupture seen at the surface actually had a total length is approximately
290 miles (470 kilometers)."  It ruptured the northernmost 430 kilometers of
the San Andreas fault from northwest of San Juan Bautista to the triple
junction at Cape Mendocino."  surprised me.

8)  A better fuller news report can be found at the San Jose Mercury News 
<A HREF="";>http://</A>
at the San Francisco Chronicle at 
or at my local paper - the Fremont Argus paper at

Ron Fong
Fremont,  CA
... i know i'm right on this one.  I've checked the facts!

In a message dated 9/26/1998 6:30:28 AM Pacific Daylight Time,
Karen12959(--nospam--at) writes:

> Study: San Andreas May Be Longer
>  .c The Associated Press 
>  SAN MATEO, Calif. (AP) -- A new study concludes that the San Andreas Fault 
> may
>  be longer than earlier thought and would cause significantly more damage if
> it
>  ruptures and triggers a major earthquake. 
>  The report released Thursday found that the section of the fault that
>  on the San Francisco Peninsula may be as long as 55 miles, not 32 miles
>  The added mileage, in the event of a major earthquake, could quadruple the
>  amount of damage to strike the San Francisco Bay area. 
>  ``It potentially exceeds Hurricane Andrew and Hurricane Hugo, and greatly
>  exceeds the Northridge quake,'' said Doug Sandy, Red Cross deputy director 
> for
>  disaster services in the San Francisco Bay area. 
>  It means the fault could produce a 7.3 magnitude earthquake rather than the
>  7.1 predicted in a previous report. In San Francisco alone, damage could be
>  three to four times as heavy as planners had estimated. 
>  Up to 107,000 homes would be left uninhabitable, up from 45,700 homes, and 
> 836
>  roads would be closed rather than 428, the report said, updating a report
>  released three years ago. 
>  The report did not contain estimates of casualties. 
>  A 300-mile stretch of the San Andreas ruptured in 1906, causing the great 
> San
>  Francisco earthquake and fire. A section of the fault broke in the Santa 
> Cruz
>  Mountains in 1989, and the Loma Prieta quake in the San Francisco Bay area 
> was
>  the result. It killed 67 people and caused $6 billion in damage. 
>  AP-NY-09-25-98 2135EDT