On 5/21/13 8:29 AM, Chris Albertson wrote:
The question here, I think was about the day-to-day shaking, not a once in
a lifetime event. Seriously if there was a 1+g acceleration who'd care if
their OCXO was still running under that pile of rubble that used to be a
house. It is the days-to-day level stuff that matters to time keeping
even a magnitude 1.0 quake is very rare for any one building even if 1.0 is
common (every day) for a geographic area. The effects are local.
hour-to-hour shaking is caused by building occupants, trucks and
construction equipment and wind. But mostly things like slamming doors and
such.
Here is a map of recent quakes near where I live. There are quite a few
but I don't know of anyone who noticed even one last week. You need
sensitive instruments to detect them over the noise of street traffic and
such.
http://www.data.scec.org/recent/recenteqs/Maps/Los_Angeles.html
All the data are there, you can look up detailed reports of each one The
web site evenhas a download page where you can get "data" with
accelerations, periods and such.
Of some casual interest is the 3.2 this morning off Pt Fermin
http://www.data.scec.org/recenteqs/Quakes/ci15345393.html
Note the depth is given as 0.3 km. That is kind of odd, because the
water depth in the channel between Catalina and Los Angeles is on the
order of a km, so one wonders what's going on.
(In fact, Google Earth gives the depth at the lat/lon as 860 meters
On Mon, May 20, 2013 at 11:47 PM, Hal Murray <[email protected]>wrote:
[email protected] said:
If the quake is strong, the temporal acceleration is on the order of 0.1
g.
See: http://en.wikipedia.org/wiki/Peak_ground_acceleration
There is a long tail on that curve. One could also define "strong" as 1 g.
The wiki page (above) lists 3 events with PGA above 2 g and several more
above 1 g. I remember a USGS report about an event in northern California
showing a big bulldozer on its side. The punch line was that the local PGA
was over 1 g. (Bulldozers have a low center of gravity. It's hard to tip
them over.)
Those are really nasty events. Distance from the quake (aka luck) is also
very important. If you are near one of them you will probably be worrying
about things other than your OCXO. (Iterate for what "near" means.)
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
