Reviewed research article Seismic activity in Iceland during 2004

• Main Authors: Sigurlaug Hjaltadóttir, Halldór Geirsson, Þórunn Skaftadóttir
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Eyjafjörður; Hengill; Katla; Langjökull; Reykjanes; Skeiðarárjökull; Tjörnes; Iceland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.618.7295; http://hraun.vedur.is/ja/skyrslur/bls107-119.pdf

Abstract — Using seismological data from the Icelandic Meteorological Office, this article summarises inland and offshore earthquake activity in Iceland during 2004. About 12,000 earthquakes were recorded during the year. The largest earthquake had a body-wave magnitude of 4.5 and it occurred on 25 September 80 km offshore from the southwest tip of the Reykjanes Peninsula. Two intense earthquake swarms occurred on the Reykjanes Ridge; one in April and the other in September. The largest swarm on the Reykjanes Peninsula comprised 1500 earthquakes; it occurred in July and was concentrated beneath the Fagradalsfjall mountain. Activity in the Ölfus-Hengill region paralleled that of the previous three years, with the largest earthquake attaining a local moment-magnitude (Mlw) of 4.2. In the South Iceland Seismic Zone, residual aftershocks occurred on the faults produced by two local Mw=6.5 earthquakes in June 2000. Two earthquake swarms were observed northeast of Langjökull in a region where earthquakes are uncommon. Earthquake activity within the western flank of the Katla volcano showed strong seasonality, peaking during the autumn as observed for decades. An earthquake swarm took place within the Katla caldera, including a Mlw 3.9 earthquake on 02 July. Seismic activity at Grímsvötn increased significantly from mid 2003 until late 2004. On 01 November, a swarm of over 180 earthquakes were recorded at Grímsvötn; at the height of this swarm, a volcanic eruption began, lasting for a week. A public warning was issued one hour ahead of the eruption. Additionally, 29 icequakes were located in Skeiðarárjökull during a jökulhlaup from Grímsvötn that began two days before the November eruption. Throughout 2004, many earthquake swarms happened in the Tjörnes Fracture Zone; the largest swarm was located at the mouth of Eyjafjörður and comprised 600 events. Swarms of similar intensity are commonplace in this region.