Strain release and strain build-up in the south Iceland seismic zone

Abstract

The south Iceland seismic zone is a 70 km long and 10–20 km broad area of land in southern Iceland where historically the most destructive earthquakes in Iceland have occurred. The zone is part of the E-W bridge between the mid-Atlantic Ridge and the neovolcanic zone, which is an eastward offset of the ridge through Iceland. The basis for the present study is a historical and an instrumental earthquake catalogue, the nature of strain release in earthquakes and as it is revealed in earthquake cracks, and observations of aseismic strain release and source propagation. The strain build-up is modelled as an interplay between the general E-W drift across the mid-Atlantic Ridge and stresses caused by the horizontal outflow of upwelling mantle material. A complex model of strain release is outlined, including seismic as well as aseismic components. While seismic strain release plays the dominant role in the eastern and central part of the zone to a depth even below 15 km, aseismic slip takes up most of the motion in the western part of the zone and in its continuation in the Reykjanes Peninsula, towards the Reykjanes Ridǵe.