Jarðskjálftar árin 1954 og 1955

Abstract

The seismograph station at Reykjavik was operated with three short period Sprengnether seismographs during these years. New stations were erected at Akureyri (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, about 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 felt on at least 21 days during 1954, three days in Northlceland 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: 1954. September 15th. About 10 shocks were felt at Grindavík. October 29th. Numerous shocks felt at Hveragerði and Hveradalir. The largest shocks were felt over area of about 7000 km-. October 30th. 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. January 15th. Considerable earthquakes at Grindavík. Macroseismic area of the largest shocks about 30000 km2. January 18th. Earthquakes felt over 8000 km- 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 13lh. Strong earthquake in South-Iceland, felt over 10000 km2. April lsl. 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 Iceland during the years covered by this report, instrumental magnitude about 5i/£. 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.