Western Slovenia is part of an actively deforming region accommodating anticlockwise rotation of Adria and its continuous collision with Eurasia. The geometry of the active faulting system in this plate boundary is not well defined. In this study, detailed analysis of earthquake activity was performed with relocation of earthquakes in the period between 2006 and 2017. With inspection of the waveform data, slight temporal clustering of activity was observed. To increase the detection rate of microearthquakes we used a matched filter detection algorithm method. Templates of earthquakes were created and a database of continuous waveform data within the period 2006-2017 was investigated. As a result, high temporal correlation allowed us to identify swarms and earthquake sequences that affected the active fault system in the study region.Relocated seismicity allowed us to constrain the geometry of 5 nearly parallel faults, namely: Ravne, Idrija, Predjama, Selce and Raša faults. All these faults do have an expression in the geomorphology and reach a seismogenic depth of up to 20 km. Vertical and along strike extents of these active faults can favour earthquakes of moment magnitude equal to 7 or larger. The most recent large earthquake that occurred in this region is the 1511 earthquake with a magnitude 6.8.The leading fault in the system being the Idrija right-lateral strike-slip fault, experiences earthquake activity from 5 to 20 km on its northern segment, while on its southern segment no earthquake activity is detected over the decade of observations. We show that the interseismic loading on the southern segment of Idrija fault is likely unclamping the locked adjacent faults promoting the observed bursts of seismicity. Moreover, in 2009 the Predjama fault accommodated a sudden increase of the surface deformation at the extensometer accompanied by a simultaneous swarm activity at its seismogenic depth. This behaviour might correspond to velocity strengthening and weakening processes taking place at both the surface and depth terminations of a locked vertical fault. These processes can be driven by a slow-slip event on the deeper part of Idrija fault that would generate a temporary acceleration of the interseismic loading rate along with a change within the fluid circulation.

Using template matching and GPS data, we investigate the evolution of seismicity and observable deformation in Central Apennines. Seismicity appears more persistent at the base of the seismogenic layer than in the shallower crust. Diffuse activity is reported on segments at depth, alternating along strike with apparent quiescence on segments that experienced one or more Mw6+ earthquakes in 1997, 2009, and 2016. Central Apennines are likely underlain by a sizeable shear zone with areas of diffuse seismicity bounding shallow normal faults where Mw6+ earthquakes occurred. The deformation observed at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain. Principal and independent component analyses of GPS data exhibit a transient when the 2016 foreshock sequence starts. This transient propagated northward from the Campotosto fault up to the Alto Tiberina fault system and has likely loaded the Mw6+ 2016 earthquake sequence. Plain Language Summary We use a nonstandard method for the detection of microseismicity at depth augmenting the available catalog. The enhanced seismicity distribution is coupled with the observable deformation on a geodetic network of continuous GPS to infer a better comprehension of the earthquake behavior. The earthquake patterns in Central Apennines reveal a segmentation at depth along an almost flat base of seismogenic layer with alternating low and high seismicity rate segments. The deformation recorded at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain also determining a possible seismic-aseismic mode. We suggest that aseismic deformation has a fundamental role in the tectonic loading and that seismicity, even if heterogeneously distributed, could represent a tracer of it. This conclusion is also supported by the evidence of a transient propagating from south to north during the 2016 Central Italy sequence.

Using template matching and GPS data, we investigate the evolution of seismicity and observable deformation in Central Apennines. Seismicity appears more persistent at the base of the seismogenic layer than in the shallower crust. Diffuse activity is reported on segments at depth, alternating along strike with apparent quiescence on segments that experienced one or more Mw6+ earthquakes in Apennines are likely underlain by a sizeable shear zone with areas of diffuse seismicity bounding shallow normal faults where Mw6+ earthquakes occurred. The deformation observed at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain. Principal and independent component analyses of GPS data exhibit a transient when the 2016 foreshock sequence starts. This transient propagated northward from the Campotosto fault up to the Alto Tiberina fault system and has likely loaded the Mw6+ 2016 earthquake sequence. Plain Language SummaryWe use a nonstandard method for the detection of microseismicity at depth augmenting the available catalog. The enhanced seismicity distribution is coupled with the observable deformation on a geodetic network of continuous GPS to infer a better comprehension of the earthquake behavior. The earthquake patterns in Central Apennines reveal a segmentation at depth along an almost flat base of seismogenic layer with alternating low and high seismicity rate segments. The deformation recorded at the surface seems to follow the seismicity variations at the base of seismogenic layer along the Apenninic chain also determining a possible seismic-aseismic mode. We suggest that aseismic deformation has a fundamental role in the tectonic loading and that seismicity, even if heterogeneously distributed, could represent a tracer of it. This conclusion is also supported by the evidence of a transient propagating from south to north during the 2016 Central Italy sequence.

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