Jökull - 01.01.2013, Blaðsíða 105

Reviewed research article
Seismicity observed under the Snæfellsjökull volcano
Florian Fuchs1, M. Lupi2, Steinunn S. Jakobsdóttir3,
Thorvaldur Thordarson4 and S. A. Miller1
1) Department of Geodynamics and Geophysics, Steinmann-Institute, University of Bonn,
Meckenheimer Allee 176, 53115 Bonn, Germany (fuchs@geo.uni-bonn.de)
2) Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland
3) Icelandic Meteorological Office, Bústadavegi 9, 150 Reykjavík, Iceland
4) School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, United Kingdom
Abstract — The Snæfellsnes peninsula in western Iceland is characterized by Pleistocene volcanism dominated
by alkalic magmatism across an extinct (> 6 Ma) axial rift zone of the Mid-Atlantic Ridge. Although Iceland
has an extensive seismic coverage, no systematic seismic monitoring is in place on the Snæfellsnes peninsula.
In this paper, we present results of a three months field campaign in the Snæfellsnes peninsula and show for the
first time that the region is (micro) seismically active in the depth range of 8–15 km. We identified and located
a total of 29 seismic events that occurred in close proximity of the Snæfellsjökull volcano, with most events
clustering beneath the volcano in swarm sequences. We propose that seismicity is associated with fluid-induced
fracturing related to one or more magmatic reservoir(s), which may be elucidated in future seismic campaigns.
Our observations are the first step towards the understanding of the plumbing system of the Snæfellsjökull
volcano.
INTRODUCTION
Volcanic and seismic activity in Iceland are driven by
the interaction of the Mid-Atlantic Ridge and the Ice-
landic Plume (Einarsson, 2008, Jakobsdóttir, 2008;
Mjelde et al., 2008). Seismicity concentrates along
the Mid-Atlantic Ridge cutting through Iceland and
separating the north-American and Eurasian plates.
Seismic activity is particularly intense in the South
Icelandic Seismic Zone (SISZ) and in the Tjörnes
Fracture Zone (TFZ) (see inset in Figure 1), which
are two transform fracture zones that accommodate
the offset of the Mid-Atlantic Ridge (Stefánsson et al.,
2006; Stefánsson et al., 2008). The axial rift was lo-
cated in the Western Fjords (WF) at 15 Ma and then
moved east towards the Icelandic plume, intercept-
ing the Snæfellsnes peninsula and the Skagi peninsula
around 7 Ma (Martin et al., 2011).
Previous studies of the Snæfellsnes peninsula fo-
cused on constraining the evolution of the neovol-
canic zone and dating volcanic activity (Jóhannesson,
1980, 1982a,b; Hardarson and Fitton, 1991; Kokfelt
et al., 2009; Martin and Sigmarsson, 2010; Martin
et al., 2011, and references therein). Figure 1 shows
the outlines of volcanic systems found on the Snæ-
fellsnes peninsula. Sigurdsson (1970) and Jóhann-
esson (1982b) pointed out the existence of WNW-
ESE trending en-echelon lineaments identified by the
alignment of volcanic structures and vents. Interest-
ingly, the orientation of these lineaments is perpendic-
ular to en-echelon patterns observed in the neighbour-
ing Western Volcanic Zone and in the South Icelandic
Seismic Zone.
The Snæfellsnes peninsula hosts three volcanic
systems that form the Snæfellsnes Volcanic Belt
(SVB). The central volcano Snæfellsjökull is located
on the westernmost tip of the peninsula (Figure 1)
and its last rhyolitic explosive eruption has been dated
to 1750 BP by Steinþórsson (1967). Located fur-
JÖKULL No. 63, 2013 105