Geodetic Strain Rates and Seismicity Rates Along the Apennines (Italy)

The Apennines are a tectonically active belt that has experienced significant earthquakes (Mw > 6). The largest events primarily occurred along the chain axis, where a complex system of normal faultsaccommodates 2–3 mm/yr of SW‐NE oriented extension, as precisely measured by a dense Global NavigationSatellite System network. Geodetic strain rates are now frequently used in earthquake hazard models; however,the impact of using such estimates, computed through different methods, for seismic hazard assessments may bedifficult to evaluate. This study explores the relationship between geodetic strain rates and seismicity rates in theApennines using three distinct horizontal strain rate maps and an instrumental seismicity catalog. We find thatthe principal directions of geodetic strain rate are kinematically consistent with those of strain release. Weestimate a spatially heterogeneous seismogenic thickness using the distribution of earthquake depths, and weisolate likely independent seismicity using three different declustering methods. We observe a correlationbetween independent seismicity rates and the magnitude of strain rate, which can be represented by either alinear or, more accurately, by a power‐law relationship. The variability in the strain‐seismicity relationshipdepends on the combination of independent seismic catalogs and strain rate maps. This relationship is primarilyinfluenced by the declustering technique more than the choice of the strain rate map and, in particular, by thenumber of aftershocks excluded during declustering. Seismicity models derived from these combinations wereused to estimate and compare the seismic moment release rate with the tectonic moment rate estimated fromstrain rate maps and seismogenic thickness. Findings indicate that the tectonic moment rate exceeds the seismicmoment release rate. We highlight uncertainties and potential causes, one of which could be a possible aseismicrelease of part of the moment rate.