An automatically generated high-resolution earthquake catalogue for the 2016-2017 Central Italy seismic sequence, including P and S phase arrival times

The 2016-17 central Italy earthquake sequence was caused by activation of an approximately 70-km-long normal-fault system comprised of a set of SW-dipping normal fault segments. The first main-shock occurred near the town of Amatrice on August 24 (MW 6.0), and was followed by a very intense and extended period of seismic activity space and time.

By the middle of September there was a dense network of 155 stations (permanent and temporary stations of the National Institute of Geophysics and Volcanology, and temporary stations from the British Geological Survey and the School of Geo-sciences at the University of Edinburgh), with a mean separation in the epicentral area of 6-8 km, comparable to the typical earthquake d epth. This network configuration was kept stable for an entire year, producing 2.5 TB of continuous waveform recordings. This database was used to generate a high-resolution catalog of earthquakes using the fully automatic Complete Automatic Seismic Processor (CASP) procedure.

The automatic procedure detected more than 450,000 earthquakes and determined their phase arrival times through an advanced automatic picker engine (RSNI-Picker2) producing a set of about 6 million P- and 9 million S-waves arrival times, which were then used to locate the events with a non-linear location algorithm (NLL) and a 1D model calibrated for the area which includes station corrections. The procedure was validated by comparison of the derived data for phase picks and earthquake parameters with a reference catalogue based on initial annual phase picking. It is fast, taking less than 12 hours to analyse the primary waveform data and to detect and locate 3000 events on the most seismically active day of the sequence.

The results show significant improvements in the number of events detected and the magnitude of completeness (from 2.5 to 0.5), as well as in resolution with an estimated error of 0.04s in P-phase picks, 0.08s in S-phase picks, 3km in epicentral location and 5km in depth, with most events having uncertainties well within these ranges. Together these provide a significant improvement in the resolution of fine structures such as local planar structures and clusters, and the identification of shallow events occurring in a previously inactive part of the crust.