Náttúrufræðingurinn - 1956, Blaðsíða 24

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NÁTTÚ R U FRÆÐIN GURINN
SUMMARY
Earthquakes in Iceland during: 1954 and 1955
by Eysteinn Tryggvason.
The seismograph station at Reykjavik was operated with three short period
Sprengnether seismographs during these years. New stations were erected at Ak-
ureyri (65°40.3' N, 18°06.0' W) and at Vík (63°25.3' N. 19°01.0' W). At both
these stations, one Mainka seismograph is operated, static magnification about
70.
The seismic activity in Iceland was rather high during these years, especially
during the period September 1954 to May 1955. At Reykjavík about 500 tremors
were recorded during 1954 and about 365 during 1955. Of these, aboul 350
in 1954 and 300 in 1955 were of local origin, epicentral distance less than 500
km. At Akureyri about 90 earthquakes were recorded during 1954 and about
70 during 1955.
Earthquakes were lelt on at least 21 clays during 1954, three days in North-
Iceland and 18 days in Southwest-Iceland. During 1955 earthquakes were
felt on at least 37 days, 24 days in North-Iceland and 15 days in Southwest-
Iceland.
The most pronounced earthquakes occurred as follows:
195-t.
September 15th. About 10 shocks were felt at Grindavík.
Octobér 29th. Numerous shocks felt at Hveragerði and Hveradalir. The lar-
gest shocks were felt over area of about 7000 km2.
October 50th. One shock felt over the same area as on October 29th.
November 21st. Several earthquakes felt at Hveragerði and Hveradalir.
Largest shocks felt over the same area as on October 29th.
1955.
Jannary 15th. Considerable earthquakes at Grindavík. Macroseismic area
of the largest shocks about 30000 km-.
January 18th. Earthquakes felt over 8000 km2 area in South-Iceland.
February 27th. Strong earthquakes in Axarfjörður, North-Iceland, where
tremors were felt on almost all days untill March 20th. Macroseismic area of
the largest shocks about 30000 km2. In the epicentral area about 200 shocks
were felt during this swarm, the maximum intensity beeing VII on modified
Mercalli scale. Minor damage was done in the epicentral region.
March 13th. Strong earthquake in South-Iceland, felt over 10000 km-’.
April lst. Strong earthquakes at Hveragerði, where minor damage was done.
The intensity of the largest shock was VII—VIII in the epicentral region, and
macroseismic area about 60000 km2. This was the largest shock occurring in lce-
land during the years covered by this report, instrumental magnitude about 5i/i.
May 19th. Earthquake felt over large area in North-Iceland, maximum
intensity about V and macroseimic area about 60000 km2. The epicenter was
situated off the north coast, east of Grímsey.