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On Oct 31, 3:55 pm, "Calif Bill" wrote:
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Did you get jostled around last night?
The in-laws in Pleasant Hill and Concord reported some pictures
knocked off the wall, etc. nothing major. Heard it was on the
Calavaras fault. Hope that doesn't set up stress in the Hayward fault.

Yes we shook fairly well. We are about 3 miles from the Calaveras fault,
but on a rocky hillside., not down in the alluvial plains that are the
valley floor around here. The Calaveras fault is much more likely to
have a
7+ quake than the Hayward according to a lot of the seismologists.
Friend
is with the USGS and is an earthquake guru and that is what he reports.
My
mom lives very near the Hayward fault as it traverses the Oakland hills.
But her house was bolted to the foundation when it was build in 1908.
Amazes some people that they figured that out back then. Thanks for
asking.
We had no damage, and only the chandelier rattled for about 5 minutes.

The in-laws in Pleasant Hill aren't on the valley floor, but are
fairly low, the underlying soil structure is chert and weathered rock,
they barely felt it. One thing that people don't understand is that
with even a moderate quake, you can very likely have some sort of
structure damage. The Richter scale doesn't tell the whole story, as
there are two factors, acceleration, and velocity. So you can likely
have some sheetrock finishing to do, etc. Glad you came out with no
damage. When I was there taking a seismic course, at the time they
were studying the Hayward fault, and had a place close to Concord that
they'd excavated like slicing through it, so they could study the soil
(liquifaction, etc.) It was interesting.
But I don't know about the Calavaras being more likely to have a major
quake, they call the Hayward a tectonic time bomb, and are stressing
that it could produce a 7+ at any time. As a slip fault, it doesn't
slip much, stores the stresses, then when friction can't hold anymore,
wham.


I know about damage. The Loma Prieta quake cracked the swimming pool.
About $5500 damage. Friend with the USGS says lot of his co-scientists
figure the Hayward is just not capable of a 7. Actually it slips a lot.
Why you can see a lot of the creep in the sidewalk and curbs.