Náttúrufræðingurinn - 1955, Síða 9

JARÐSK.TÁLFTAR
71
SUMMARY:
Eartliquakes by Eysteinn Tryggvason.
This is mainly a translation of an article by Dr. B. Gutenberg in ,,SPHERE“,
November 1952, and gives a general information al>out the present status of the
seismological science.
Some informations about icelandic earthquakes are given:
Two major earthquakes (magnitude 7.0 to 7.7) have occurred in Iceland during
this century, on January 22nd, 1910, epicenter off the North Coast, magnitude 7.1,
and May 6th, 1912, in South-Iceland, magnitude 7.0. Magnitude of the earthquake
in South-Iceland on August 26th, 1896, was probably about 7l/2, and that of August
14th, 1784, was still larger.
The average number of earthquakes of magnitude 5 and more in Iceland is ahout
one per year. Three such shocks have occurred since January lst, 1952, until April
lst, 1955; on March 12th, and May 16th, 1952, and January 15th, 1955. The epi-
centers of all this shocks were near Krísuvík (63°53'N, 22°04'W). The earthquake
in Hveragerdi (63°00'N, 21°12'W) on April lst, 1955, was larger than these three,
and the largest earthquake in Iceland since October 9th, 1935. Tlie magnitude of
the earthquake in South-Iceland on October 9th, 1935, was about 6.
Of the present average of about 220 great shocks (magnitude over 7.7), about
1200 major earthquakes (magnitude 7.0 to 7.7), and about 11000 earthquakes of
magnitude 6.0 to 6.9 per century over the whole earth, about 25 large earthquakes
(magnitude 7.0 to 7.7) and about 200 shocks of magnitude 6.0 to 6.9 occurres in
the Atlantic seismic belt, and in Iceland or its immediate vicinity the number is
2 to 4 major earthquakes and 10 to 20 earthquakes of magnitude 6.0 to 6.9 per
century. No or very few large shocks (magnitude more than 7.7) occur in the At-
lantic seismic belt.