| Summary: | In this study, we analyze the 2020 earthquake swarm on the Reykjanes Peninsula by moment tensor inversion in order to improve our understanding of the seismogenic processes and their relation with magmatic and tectonic activities. The densified seismic monitoring operational during the study period provides a unique dataset for the seismic sequence preceding the 2021 Fagradalsfjall eruption. We perform full moment tensor (MT) inversion for 85 earthquakes with magnitudes Mw > 2.5 using a probabilistic approach. For the first time, we attempted to integrate DAS data into the MT inversion. Focal mechanisms exhibit predominantly strike-slip faulting with a few normal faulting events and are overall compatible with the regional tectonic regime. Earthquake foci are shallow with an average depth of 3 km. We estimate robust, significant, positive isotropic components contributing up to 15% to the moment release. We hypothesize that the origin of such significant non-double-couple (non-DC) components may be attributed to volume changes accompanying the surface uplift and rifting processes in the region. Our study demonstrates that non-DC earthquake source components can be monitored prior to eruption and potentially, their identification may be used as indicator for magma intrusion in the shallow crust.
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