Rapid Changes in 1 - 4 Hz Continuous Tremor, GrÝmsfjall
- Subject: Rapid Changes in 1 - 4 Hz Continuous Tremor, GrÝmsfjall
- From: "Matthew J. Roberts" <firstname.lastname@example.org>
- Date: Mon, 08 Nov 2004 12:09:13 +0000
- Organization: Physics Department, Icelandic Meteorological Office
- Reply-to: email@example.com
- User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.2)
In the last two days, we have observed distinct periods of reduced seismic
tremor in the 1 - 4 Hz frequency range at GrÝmsfjall. (See enclosed GIF
images.) For instance, at ~0220 hours, ~0415 hours, and ~0740 hours on 06
November, tremor intensity decreased abruptly and then rose steadily to
pre-existing levels. The rapidity of the tremor changes are suggestive of
changes in hydraulic resonance rather than meteorological conditions.
Recent photographs on Magn˙s' Web-site show water draining from GrÝmsv÷tn
into Skeiarßrj÷kull; see:
Perhaps the sudden variations in 1 - 4 Hz tremor are due to the development of
water-flow constrictions within the (rapidly healing) ice dam?
Additionally, see http://hraun.vedur.is/ja/oroi/grf.gif
for an overview of recent tremor data from GrÝmsv÷tn. Note that the higher
frequency measurements remain elevated above pre-j÷kulhlaup conditions. More to
follow in a separate message from KristÝn on spectrograms derived from recent
Eftirlitsmaur 45. viku ß Elisfr.svii Veurstofu ═slands
P.S. The following URL is still being up-dated, so please stay tuned!