A Consistent and Uniform Research Earthquake Catalog for the AlpArray Region.

The AlpArray research initiative (www.alparray.ethz.ch) started in 2016 with the aim of investigating the geodynamics of the European Alps and their forelands from crust to mantle. The associated AlpArray Seismic Network (AASN) is composed of more than 650 broadband seismic stations (300 of which are temporary) thus providing unprecedentedly uniform station coverage for the region that exhibits a significant yet laterally strongly variable seismicity presently monitored and reported by a dozen individual observatories. A homogeneous earthquake catalog in terms of location and magnitude is a prerequisite to improve our understanding of the seismotectonics and the seismic hazard in the greater Alpine region.

We take advantage of this new large data set to provide consistent and precise hypocenter locations and to provide preliminary but uniform magnitude calculations across the region. Focusing on the first two years of data (2016-2017) from more than 1000 stations (> 20TB of data), we first use the SeisComP3 monitoring system STA/LTA detector system in off-line mode for events detection. After an initial location is provided, a high-quality semi-automated re-picking approach defines the consistent phase arrival times in combination with timing uncertainties and phase identification assessment. This automatic re-picking framework is pursued by QUAKE, an object oriented Python library which, by means of a multipicking stage, takes advantage of different well established picking algorithm to exploit different waveform's information, both frequency- and energy- related.

Subsequently, the high-quality automatic picks of all well-locatable earthquakes are used to calculate a minimum 1D P-wave velocity model for the region with appropriate stations corrections. Finally, all events are relocated with the NonLinLoc algorithm in combination with the updated 1D model. We compare our locations with existing earthquake catalogs (ISC, EMSC, national catalogs). The proposed procedure represents an important step towards the uniform earthquake catalog for the entire greater Alpine region using the AASN.