Jökull - 01.01.2005, Page 96

Heidi Soosalu and Páll Einarsson
4
6
8
10
12
14
16
ln
o
f i
nt
en
si
ty
17 18 19 20 21 22 23 24
17 Jan 1991
HAU-Z 2000
SAU-Z 2000
SAU-Z 1991
-1
0
1
2
3
M
L m
ag
ni
tu
de
(16:32)
BUR strain
contraction starts
eruption starts
(17:02) (18:40)
BUR strain
contraction stops
-1
0
1
2
3
M
L m
ag
ni
tu
de
17 18 19 20 21 22 23 24
26 Feb 2000
BUR contr.
starts
(17:45)
eruption starts
(18:19) BUR contr.
stops (19:20)
Figure 6. Temporal distribution of the earthquakes around the onset of the 1991 and 2000 eruptions with their
ML magnitudes (scale to the right), the onset times are aligned at the same line. The magnitude scale is on the
right. Changes in strain are also marked. Tremor intensity curves, for SAU in 1991 (dashed line), and HAU and
SAU in 2000 (bold lines) are shown, as well (scale to the left). Only the vertical components (Z) are shown.
The horizontal components had similar, slightly higher values. High peak in the very end of the SAU 1991
curve is an artefact. The frequency band used is 0.5–3.0 Hz, to damp the effect of the low-frequency micro-
seism of oceanic origin and the high-frequency earthquakes. The intensity is calculated as averaged energy over
60-second intervals, and its natural logarithm is plotted. – Skjálftavirkni í tengslum við gosbyrjanir 1991 og
2000. Stærð skjálfta (ML) er sýnd sem fall af tíma fyrir bæði gosin. Tímakvarðinn er sá sami fyrir bæði gosin
og upphafstímar gosanna eru látnir standast á. Styrkur óróans er einnig sýndur sem fall af tíma eins og hann
kemur fram á mælum í Saurbæ (SAU) og Haukadal (HAU). Einungis lóðrétti þátturinn er sýndur. Óróagögnin
eru bandhleypisíuð á bilinu 0.5–3.0 Hz til að útiloka truflanir frá úthafsöldum og hátíðniskjálftum. Styrkurinn
er reiknaður sem 60 sekúndna meðaltal af orku.
96 JÖKULL No. 55