Microseismic activity in the Eastern Alps: Sequences, mechanisms, and active faults

The southern and eastern Alps are a fascinating target region for a seismological study because they include the deformation front of Adria-Europe convergence with historically significant events (e.g., M 6.0 Friuli 1976) as well as areas where seismicity seems more or less absent despite geologically mapped large fault systems and past deformation fronts. The large-N installations of the Swath-D (2017-2019) and AlpArray (2016-20219) seismic networks provide unmatched opportunities to study the microseismicity in the Eastern Alps in unprecedented detail. For the first time in the study area, the homogeneous station spacing allows a consistent analysis of seismicity across the entire area. These detailed seismological analyses provide the opportunity to characterize deformation in the upper 15 km of the crust.
We show how a combined workflow, including clustering, relocations, and MT inversions, sheds light on the seismicity and the ongoing active deformation. We observe strong zonations of seismic activity rates, sequence characteristics, and rupture mechanisms, coinciding with dominant tectonic deformation styles and subsurface properties such as Qp attenuation. We identify and characterize multiple likely unknown fault systems that experience local stresses deviating from the regionally dominant Adria-Europe convergence. Our findings agree well with the occurrence of large historical earthquakes while simultaneously shedding light on much smaller seismogenic features.