First results from the North Iceland experiment
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ORIGINAL PAPER
First results from the North Iceland experiment C. Riedel Æ A. Tryggvason Æ B. Brandsdottı´r Æ T. Dahm Æ R. Ste´fansson Æ M. Hensch Æ R. Bo¨ðvarsson Æ K. S. Vogfjord Æ S. Jakobsdottı´r Æ T. Eken Æ R. Herber Æ J. Holmjarn Æ M. Schnese Æ M. Tho¨len Æ B. Hofmann Æ B. Sigurdsson Æ S. Winter
Received: 25 April 2005 / Accepted: 7 August 2006 / Published online: 14 September 2006 Springer Science+Business Media B.V. 2006
Abstract Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjo¨rnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms
C. Riedel Æ T. Dahm Æ M. Hensch Æ R. Herber Æ M. Schnese Æ M. Tho¨len Æ B. Hofmann Æ S. Winter Institut fu¨r Geophysik, Bundesstr. 55, 20146 Hamburg, Germany A. Tryggvason Æ R. Bo¨ðvarsson Æ T. Eken Institutionen fo¨r Geovetenskaper, Avdelningen fo¨r Geofysik, Villava¨gen 16, 75236 Uppsala, Sweden B. Brandsdottı´r Science Institute, University of Iceland, ¨ skju, Sturlugata 7, 101 Reykjavı´k, Iceland O R. Ste´fansson Æ K. S. Vogfjord Æ S. Jakobsdottı´r Æ J. Holmjarn Physics Department, Meteorological Office of Iceland, Bustadavegur 9, 150 Reykjavı´k, Iceland B. Sigurdsson Marine Research Institute, Skulagata 4, 121 Reykjavı´k, Iceland Present Address: C. Riedel (&) Centro de Vulcanologia e Avaliac¸ao dos Riscos Geologicos, Ponta Delgada, Ac¸ores, Portugal e-mail: [email protected]
offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system. Keywords Broadband seismology Æ Multibeam bathymetry Æ Hot spot-ridge interaction Æ Iceland Æ Ocean bottom seismology Æ Tjo¨rnes fracture zone
Introduction The north of Iceland represents in many ways an extraordinary geological setting. In 1974, Sæmundsson gave a first good tectonic and geological description of a region where the Mid-Oceanic Ridge changes from an offshore to an onshore ridge, separated by a transform zone. However, this transform zone is leaky and shortly after publishing the geological review of Sæmundsson (1974) a subaerial fissure eruption along the Krafla fissure swarm (Fig. 1) between 1973 and 1983 revealed its volcanic potential. Strong earthquakes above magnitude 7 make it the primary focus of highenergetic seismicity in and
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