Náttúrufræðingurinn - 1955, Blaðsíða 91

JARÐSKJÁLFTAR Á ÍSLANDI
197
SUMMARY
Seismicity of Iceland and the Surrounding Oceans.
by EYSTEINN TRYGGVASON
The seismograph station at Reykjavík is very important in locations of epicen-
ters in Iceland and the surrounding oceans. This station has been in continous
operation since 1926, although most of the time, the instruments have been rather
primitive.
The author has tried to locate all epicenters in a region boundered by latitudes
at 50° and 80° north, the west coast of Great Britain and Norway, and the east
coast of Greenland and longitude 40° west. This investigation takes over the period
1927 to 1945 incl.
The data are mostly taken from International Seismological Summary, although
no epicenter has been adopted without critical examination. In most cases, the
epicenters from I. S. S. have been revised. It is belived, that all earthquakes of
magnitude §514 have been included in the study. Epicenters of smaller earth-
quakes can not be located with necessary accuracy.
It has been found, that during the period covered by the investigation, 121 earth-
quakes, large enough to be located, have occured in this region. The revised epi-
centers are shown on the map, which shows clrearly the northernmost part of the
Atlantic seismic belt. The earthquakes are divided into three groups after magni-
tude. Only 4 shocks of magnitude §6% have occurred, 24 shocks of magnitude
5%—6, and the remaining 93 shocks are of magnitude 5*4—5*4- Determination
of the magnitude is very unaccurate, as it depends on how well the shocks are
registered at distant stations.
The highest seismicity is observed on the south-west end of the Reykjanes ridge,
near 56° N, 35° W. The part of the seisntic belt nortli of latitude 70 is beauti-
fully arc shaped, and its form resemhles that of the seismic arcs of pacific type.