Seismicity Rate Changes and Geodetic Transients in Central Apennines

Abstract

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.

Post-Seismic Deformation Related to the 2016 Central Italy Seismic Sequence from GPS Displacement Time-Series

“…The other two hydrological components ( IC3 and IC4 An additional analysis performed on the pre-seismic time-span (Section 2.3) does not show components that can be clearly associated with transient tectonic deformations. In particular, we do not find evidence of a preparatory phase prior to the Amatrice mainshock (Text S2) similar to the one described in Vičič et al (2020).…”

Post‐Seismic Deformation Related to the 2016 Central Italy Seismic Sequence From GPS Displacement Time‐Series

“…An additional analysis performed on the pre-seismic time-span (Section 2.3) does not show components that can be clearly associated with transient tectonic deformations. In particular, we do not find evidence of a preparatory phase prior to the Amatrice mainshock (supplementary material S2) similar to the one described in Vičič et al (2020).…”

“…The results, reported in Text S2, show that the temporal and spatial parts of the independent components retrieved in this time span do not highlight any localized deformation signal that can be associated with a clear tectonic strain transient, such as the sudden rise at the beginning of 2016 described by Vičič et al. (2020). It is worth considering that with respect to Vičič et al.…”

“…The results, reported in Text S2, show that the temporal and spatial parts of the independent components retrieved in this time span do not highlight any localized deformation signal that can be associated with a clear tectonic strain transient, such as the sudden rise at the beginning of 2016 described by Vičič et al (2020). It is worth considering that with respect to Vičič et al (2020), we handle differently the missing data and analyzed three-dimensional time-series, while they described a "precursory" signal when analyzing only the east component. A more detailed analysis of the eventual pre-seismic slip is left for future work, since here we want to focus on the modeling of the post-seismic deformation.…”

Post-seismic deformation related to the 2016 central Italy seismic sequence from GPS displacement time-series

“…We also investigate the pre-seismic phase, limiting the analysis to the 2015-2016.64 (i.e., the 24th of August) time-interval as in Vičič et al (2020), in order to detect possible deformation signals that can be associated with the preparatory phase of the 2016 earthquake sequence. According to an F-test, the most suitable decomposition is the one with L = 4 components; we carry out the decomposition on the whole GPS network (see Figure 2).…”