ALBERT

Description: The Alps as the result of the convergence of the African and European plates represent extremely complex struc-tures and kinematics. The Southern and Eastern Alps as part of this continental collision are the target area of thecurrent study. In this region, the Priadriatic Fault is sinistrally offset by the Guidicarie Fault and a switch in the sub-duction polarity had been proposed. In order to better understand the crustal and upper-mantle structure and how itis related to faults seen at the surface, we aim to assess the precise distribution of local earthquakes (potentially in-dicating active faults) and the seismic velocity structure in the subsurface. In our investigation, we use the data of avery dense seismic network deployed in the Southern and Eastern Alps (SWATH-D network - DFG funded priorityProgramme 4D-MB) to provide seismicity pattern and velocity structure of the crust and possibly the upper mantle.This temporary network consists of 150 stations with an average inter-station spacing of 15 km complementingthe larger scale AlpArray Seismic Network (AASN). The objectives are, accordingly, to implement a reliable andfully automated algorithm to detect the events and pick the phase onset times of local earthquakes, provide precisehypocentral locations and calculate a velocity model for the target area. Here we focus on the first results of theearthquake analysis procedure and present a 1-D velocity model for the Southern and Eastern Alps. Later, this datawill be used for a 3-D tomographic inversion. So far, we used 10 months of data from September 2017 to Jun 2018and implemented an automated multi-stage processing chain to provide the first catalog. The catalog comprises123 local earthquakes with 5261 P and 2651 S picks. The hypocentral locations were then calculated and a 1-Dvelocity model was also obtained using simultaneous inversion of hypocenters, velocity, and station corrections.The seismicity pattern is characterized by rather diffuse clusters in the Friuli, Lake Garda, Brenner and Trentinoregions with low to medium magnitude (ML 0-4) events within the upper 25 km of the crust. The central part ofthe region, where the Preadriatice fault sinistrally offset by the Guidicarie Fault and its related fold-and-thrust belt,has obviously less activity. Our 1-D velocity model indicates upper crustal velocities that are higher than averagefor the whole Alpine region.