PSN-L Email List Message

Subject: Re: Earthquake strength
From: Steinar Midtskogen steinar@.............
Date: Thu, 10 Jul 2008 06:56:31 +0200

[Jón Frímann]

> Local earthquakes have higher frequancy compnment then telesesmic
> earthquakes (more then 1500 km away).  Due to that fact a 30 second
> sensor won't detect local earthquakes well or not at all. For optimal
> dection of local and regional earthquakes you need a sensor that is 1Hz,
> but geophones up to 4,5Hz also work quite well. But are not as senstive
> to smaller earthquakes, by best dection is ML0,5 (unchecked size) at 18
> km.

I think I can expect several <1.5 earthquakes a year here in the Oslo
region and perhaps a couple of slightly stronger ones which are
usually not felt, but there hasn't been one yet to provide a test.

However, a brief thunderstorm a few days ago was clearly visible on
the plot for about 20 minutes, which matched the period lightnings
were striking within a distance of few hundred metres.  The rain was
also very heavy (14 mm in 10 minutes), but I don't know if that can
influence the seismometer.

I've been wondering whether a geophone would be something to get, but
I suspect that my site isn't very suited, since rail lines pass 40
meters away.

Steinar Midtskogen

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