Full Moment Tensor Inversion for the Characterization of Seismogenic Sources in the Pollino Area (Italy)

The objective of this work is the estimation of the moment tensor, with particular attention to the analysis of the full moment tensor, to kinematically characterize the seismogenic sources in the shallow crust of Mt. Pollino area (Southern Italy). The moment tensor analysis is an indispensable tool for understanding the rupture process, determining the fault geometry, the characteristics of the medium in the seismogenic volume, and the acting stress field. In regions with a complex tectonic structure, such as the Mt. Pollino area, the double couple model may not be sufficient for characterizing seismogenic sources. The inversion of the full moment tensor is essential to analyze also the non-double couple components, which can give very important insights in case of complex sources. Furthermore, the full moment tensor solution is of fundamental importance for verifying and estimating possible volumetric variations in the focal volume.

In this study, the dataset consists of 65 earthquakes that occurred in the Pollino area between latitudes 39.70 and 40.10 and longitudes 15.80 and 16.30 from 2010 to 2024, characterized by magnitudes 2.5<M<5.0 and a maximum depth of 10 km. The inversion of the full moment tensor was performed using "Grond" (Heimann et al. 2018), a software based on the comparison between synthetic and observed signals through a Bayesian probabilistic approach. We used seismic data at local to regional distances; the data were deconvolved to remove the instrumental response and transformed into displacement. The inversion is based on the fitting of full waveforms, on the three components, in the 0.04 - 0.10 Hz frequency band. The inversion was performed under the hypothesis of point source by applying the L1 norm for the “double couple”, “deviatoric” and “full” moment tensor configurations, using three different crustal velocity models to check the stability of the results. We obtained a stable solution for 50 earthquakes, all of them characterized by normal kinematics with strike in the NW-SE direction, and a predominant positive isotropic component. Positive values up to 53% of the isotropic component indicate tensile opening processes, thus suggesting that the seismicity may be affected by fluid transfer.