Rapid Changes in 1 - 4 Hz Continuous Tremor, GrÝmsfjall



SŠl ÷ll,

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:

http://www.raunvis.hi.is/~mtg/04gv/041105-129SG.JPG
http://www.raunvis.hi.is/~mtg/04gv/041105-115SG.JPG

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 GrÝmsfjall data.

Kve­ja,

Matthew.
Eftirlitsma­ur 45. viku ß E­lisfr.svi­i Ve­urstofu ═slands

P.S. The following URL is still being up-dated, so please stay tuned!
http://hraun.vedur.is/ja/eldgos_grimsvotnum.html




GIF image

GIF image