Preliminary Analysis of the 21 February 2008 Svalbard (Norway) Seismic Sequence

Abstract

The Svalbard Archipelago is situated in the northwestern part of the Barents shelf, in close proximity to the passive continental margin. This intraplate region is characterized by some of the highest seismicity in the entire Barents Sea and adjoining continental shelf, surpassed only by the Knipovich ridge ( e.g. , Engen et al. 2003; International Seismological Centre 2001), which, as a spreading plate boundary, is the structure that dominates the regional stress field. Most of the seismic activity (Figure 1) is characterized by smaller events, which often occur in small concentrations sparsely distributed in time. However, earthquakes of moderate to stronger magnitudes do occur in the Svalbard area, such as the 4 July 2003 mb 5.7 event close to Hopen Island ( e.g. , Stange and Schweitzer 2004). A more recent example will be discussed here: the Mw 6.0 earthquake that occurred in Storfjorden, off the coast of the island of Spitsbergen, on 21 February 2008 and initiated an extensive aftershock sequence. The data presented in this contribution cover approximately seven months following the occurrence of the mainshock and involve more than 250 aftershocks included in the NORSAR Regional Reviewed Bulletin (http://www.norsardata.no/NDC/bulletins/regional/), which contains events with an automatic network magnitude ( MGBF ) larger than 2.0. The 2008 seismic activity in Storfjorden coincided temporally with an International Polar Year (IPY) project to study the continental margin in the region between the Mohns and Knipovich ridges and Bear Island, south of Spitsbergen (see http://www.norsar.no/c-24-International-Polar-Year.aspx). This resulted in the mainshock and a significant part of the aftershock sequence being recorded by several temporary seismic stations deployed in the region, in addition to the permanent installations in the European Arctic. Data used in this study were obtained from the NORSAR arrays SPITS and ARCES; the Norwegian National Seismic Network (NNSN) stations KBS, BJO1, and …