[time-nuts] OCXO shock protection

Jim Lux jimlux at earthlink.net
Tue May 21 13:57:51 EDT 2013

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

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 <hmurray at megapathdsl.net>wrote:
>> tvb at LeapSecond.com 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.)

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