Jökull - 01.01.2019, Page 73

Pálsson et al.
Figure 1. Map of the study area around the Bárðarbunga volcano, showing epicenters of the period of unrest,
2010–2017. The inset map shows the volcanic systems of Iceland according to Einarsson and Sæmundsson
(1987) as modified by Hjartardóttir et al. (2016a). – Kort af Bárðarbungu og rannsóknarsvæðinu umhverfis
hana. Punktar sýna skjálftamiðjur jarðskjálfta sem urðu á umbrotasvæðinu 2010–2017. Innfellda kortið sýnir
eldstöðvarkerfi á Íslandi.
tive is to use the b-value of a region for monitoring
purposes as a proxy for stress (see e.g., Kulhanek,
2005 for summary). Furthermore, consistently high
b-values are expected in crustal volumes where the
strength is low, as for example in volcanic areas where
magmatic heat has an effect on rock properties (e.g.,
Wiemer et al., 1998; Riedel et al., 2003) preventing
large earthquakes. A comprehensive review of previ-
ous investigations into the spatial and temporal vari-
ations of b-value suggests that they are most plausi-
bly linked with changes in effective stress (El-Isa and
Eaton, 2014).
Three volcanoes in Iceland show an unusually
continuous and persistent seismic activity, Hengill,
Katla, and Bárðarbunga (Einarsson, 1991a). The seis-
mic activity of the Bárðarbunga volcano offers a good
opportunity to study the frequency-magnitude distri-
bution of earthquakes in a relatively isolated envi-
ronment (Figure 1) and relate it to tectono-magmatic
events that have taken place there in recent years. This
volcano has been going through phases of large earth-
quakes 1974 to 1996 (Einarsson et al., 1997; Bjarna-
son, 2014), relative quiescence 1996 to 2002, in-
creasing seismicity 2002 to 2014 (Jakobsdóttir, 2008),
72 JÖKULL No. 69, 2019