PSN-L Email List Message

Subject: Re: Relevelling
From: Steinar Midtskogen steinar@.............
Date: Tue, 29 Jul 2008 22:43:48 +0200


> In a message dated 2008/07/29, steinar@............. writes:
>     I've had a SEP seismometer running for a month or so and everything
>     has been fine.  However, a couple of days ago while we were away on
>     vacation it began reporting no activity.  When I got back home I found
>     that the mass had moved all the way to the side, so I had to change
>     the tilt a little so it would move back to the centre again.

>        Has there been any rain while you have been away? This is a
> common cause of real ground tilts. Did you switch off the heating
> while you were away?

No rain.  Hardly a cloud.

No changes to the heating.  There is no heating in that room and the
temperature there is extremely stable.  I have a temperature sensor
there and for the day it happened I logged a maximum of 21.33C and a
minimum of 21.04C.  I don't think one can get a more stable
temperature than that.  Humidity ranged from 38.7% to 43.9%.

The only thing out of the ordinary is that the outside temperature
during the past days reached a high of 29.4C which is a new record for
the 5 years I've been recording the weather.  The ground temperature
is very high as well, 18C as deep as 50 cm, something which I don't
think I've recorded before.

>        Have you fitted metal ground plates under the adjustment screws?

Yes, but they're not bolted or otherways attached to the floor.

> I use about 8 cm square x 2.5 mm thick SS.

They're around 3x3 cm and 1-2 mm thick.

>        Something has happened in your absense. The only question is
> what and can you avoid it happening again?

True.  I guess I might have to wait for it to happen again and see if
that offers more hints.



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