Single and joint fault plane solutions for microearthquakes in South Iceland

Abstract

We obtain fault plane solutions for a swarm of twelve events and two single events ranging in magnitude between −0.3 and 3.1. The events were recorded by a local network in South Iceland, consisting of eight three-component stations with approximately 30 km between the stations. For events larger than M L −1 the solutions are well constrained. The non-uniqueness of the fault plane solutions increases with diminishing magnitude. To enhance the uniqueness of the fault plane solutions for the earthquake swarm, we search for mechanisms with a common fault plane but possibly varying slip directions in that plane. Data for all the events are consistent with faulting on a common plane. Relative location of the events shows that they all occurred less than 11 m from a single plane. Fault plane solutions for all the analysed events of the swarm, as well as the two single events, are consistent with strike-slip-dominated faulting on faults striking roughly north-south. The results are in agreement with the strikes of mapped surface fractures and focal mechanisms of larger earthquakes in the area. This indicates that the microseismicity is related to the same pattern of regional deformation as the major earthquakes in South Iceland.