Centroid Moment Tensor Catalog With 3D Lithospheric Wave Speed Model: The 2016-2017 Central Apennines Sequence

Moment tensor inversions of broadband velocity data are usually managed by adopting Green's functions for 1D layered seismic wave speed models. This assumption can impact on source parameter estimates in regions with complex 3D heterogeneous structures and discontinuities in rock properties. In this work, we present a new centroid moment tensor (CMT) catalog for the Amatrice-Visso-Norcia (AVN) seismic sequence based on a recently generated 3D wave speed model for the Italian lithosphere. Forward synthetic seismograms and Frechet derivatives for CMT-3D inversions of 159 earthquakes with M-w >= 3.0 are simulated using a spectral-element method (SEM) code. By comparing the retrieved solutions with those from time domain moment tensor (TDMT) catalog, obtained with a 1D wave speed model calibrated for Central Apennines (Italy), we observe a remarkable degree of consistency in terms of source geometry, kinematics, and magnitude. Significant differences are found in centroid depths, which are more accurately estimated using the 3D model. Finally, we present a newly designed parameter, tau, to better quantify and compare a-posteriori the reliability of the obtained MT solutions. tau measures the goodness of fit between observed and synthetic seismograms accounting for differences in amplitude, arrival time, percentage of fitted seconds, and the usual L2-norm estimate. The CMT-3D solutions represent the first Italian CMT catalog based on a full-waveform 3D wave speed model. They provide reliable source parameters with potential implications for the structures activated during the sequence. The developed approach can be readily applied to more complex Italian regions where 1D models are underperforming and not representative of the area.

Automated summary

Moment tensor inversions using 1D models may be inadequate for regions with complex 3D structures. This study presents a new CMT catalog for the Amatrice-Visso-Norcia seismic sequence based on a 3D wave speed model. The solutions obtained using the 3D model show consistency with those from a 1D model in terms of source geometry, kinematics, and magnitude. A new parameter, tau, is introduced to assess the reliability of the MT solutions.