Jökull - 01.06.2000, Page 68

Earthquakes in the Mýrdalsjökull area, 1978–1985
2
3
4
1978 1979 1980 1981 1982 1983 1984 1985
M WESTERN MÝRDALSJÖKULL
2
3
4
1978 1979 1980 1981 1982 1983 1984 1985
M EASTERN MÝRDALSJÖKULL
2
3
4
1978 1979 1980 1981 1982 1983 1984 1985
M MÝRDALSJÖKULL
Figure 6. Magnitude of Mýrdalsjökull earthquakes as a function of time. Magnitude of all events during
1978-1985 (top) along with their division into events east (center) and west (bottom) of 19.24 W. Events within
each cluster were located with an accuracy better than 5 km in the horizontal direction. – Stærðir skjálfta við
Mýrdalsjökul sýndar sem fall af tíma. Efst eru allir jarðskjálftar (samtals 385) sem staðsettir voru með minni
óvissu en 5 km í lárétta stefnu, en á neðri myndunum sést skipting þeirra á milli svæða.
TEMPORAL BEHAVIOUR OF
SEISMICITY
The annual cycle of seismicity within the Mýr-
dalsjökull region noted by Tryggvason (1973) for the
period 1952-1958 is confirmed by the present study.
The annual cyclic pattern has continued to the present
day (2000) and is, thus, shown to have persisted for
more than four decades. Separating the activity be-
tween the western and the eastern clusters, it is evident
that the annual cyclicity is much more pronounced in
the western cluster (Figures 4, 6 and 7). It turns out
that all deviations from the pattern are attributable to
the eastern cluster where the seismicity fluctuates con-
siderably from year to year. Whereas the seismic ac-
tivity is highest in both clusters during July-October,
almost no events occur in the western cluster during
the first half of the year. In fact, the eastern clus-
ter by itself does not have a strong seasonal cyclic-
ity although the seismicity there has often culminated
in August (Figure 4). In contrast, the western cluster
shows a highly regular pattern.
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