Identifying seismogenic faults: Case studies from SW Iceland

Many large earthquakes originate from either poorly constrained or unknown faults, making hazard assessment difficult in earthquake-prone regions. Here we demonstrate the utility of integrating results from field surveys, seismic observations, and remotely sensed data to identify earthquake faults on the Reykjanes Peninsula, Iceland. This Peninsula is an oblique segment of the Mid-Atlantic ridge, and because of its extreme obliquity with respect to the direction of absolute plate motion, it experiences both extension and shear, resulting in slip along both normal and strike-slip faults. Large normal faults and eruptive fissures are prominent on the Peninsula, but strike-slip faults have a much less obvious surface expression. Since 1998, six earthquakes with local magnitudes around five have occurred on the Peninsula, with seismic and geodetic data indicating their occurence along generally north-striking, right-lateral, strike-slip faults. Only one of these faults had been mapped previously, and primary rupture associated with the earthquakes was found along only two faults. Survey work along faults subject to aftershock activity constrained surface disruption paralleling local topographic features and structural lineaments. We review the above examples and explore the feasibility of using similar techniques in order to identify seismogenic faults in SW Iceland before damaging earthquakes occur. We will illustrate how GIS is allowing time-dependent insights into the seismic history of the Reykjanes Peninsula.