A new 3D P-wave velocity model for the greater Alpine Region from 24 years of local earthquakes data.

The European Alps and its surrounding mountain belts (e.g., the northern Apennines, the northwestern Dinarides, and the western Carpathians) forms a tectonically complex system, referred as the “greater Alpine region” (GAR). Although being extensively  investigated, the evolving dynamic tectonic system and microplates relation are still under debate.

From 2016-2019 the AlpArray project, with its seismic network of ~700 broadband sensors, created an unprecedented chance to uniformly investigate the recorded seismicity in the GAR. After the successful compilation of the AlpArray research seismicity catalog (AARSC, Bagagli et al., 2022) we took a major leap to repick the seismicity reported by the European-Mediterranean Seismological Centre (EMSC) from May 2007 to December 2015. We use the same approach as for the AARSC to repick and consistently relocate 1397 events. Eventually, we consistently and homogeneously re-calculated the local magnitudes on the vertical component only (MLv). This allows a better data selection for the inversion stages, avoiding the magnitude scales mixing reported in bulletins. In addition to these two dataset, we also use the already published dataset for the latest GAR tomography spanning the time-period from January 1996 to May 2007 (Diehl et al., 2009). These three combined dataset have an average picking error observations of 0.2 seconds and provide an unique opportunity to perform a local earthquake tomography (LET) in the GAR.

We select 2343 MLv >=2.5 well-locatable events (azimuthal gap <180 degree, number of P-observations > 7) for the calculation of a new Minimum 1D model for the GAR. For the inversion procedure, we select 2285 events for a total of 84664 rays. The 99% of the rays are shorter than 350 km. We use SIMULPS software to derive the 3D P-wave velocity model using a model parametrization of 20x20x10 km cells in the well-resolved area. 

The preliminary velocity model correctly delineates the GAR major tectonic features, and due to the dense ray coverage it provides excellent resolution of the shallow crustal heterogeneities. This model will help the seismological community push forward the understanding of the GAR geodynamics.