The new seismic catalog of the Gargano area (Southern Italy) after a decade of seismic monitoring by OTRIONS network

Abstract

The Gargano Promontory (hereafter GP) has attracted the attention of seismologists in recent years for its peculiarities regarding the high rate of low-magnitude seismicity and focal depths in the lower crust. These peculiarities have been highlighted thanks to the new data provided by the OTRIONS seismic network (hereafter OT), installed in 2013 in the GP area, consisting of 15 short-period seismometers, thanks to a fruitful collaboration between UniBa (University of Bari Aldo Moro) and INGV (Istituto Nazionale di Geofisica e Vulcanologia). The first available seismic catalog referred to the first 7 years of the network operation (2013–2018) and suffered from some technological problems of the acquisition system. Thanks to improvements in the data transmission system, these problems were overcome in 2019 and now the OT network data are available in real time. In order to include the most recent seismicity and to cover the temporal gaps existing in the previous catalog, we thoroughly reviewed the 24 h seismic recordings, collected over the decade after the installation, by employing an automatic detect and picking software (CASP, Complete Automatic Seismic Processor). More than 7100 seismic events were initially identified. Through careful manual review, approximately 60 % were confirmed as local earthquakes, and the others were recognized as quarry blasts or false/poorly-located events. Manual review significantly improved the quality of P- and S-phase picking, and consequently led to more accurate earthquake locations, using both linearized and nonlinear algorithms. The manual review resulted in two catalogs, both released on Mendeley Data (https://doi.org/10.17632/nhfvx7ysxw.6). This study highlights the value of automatic analysis for compiling a seismic catalog, suggesting that the manual review is still necessary. The quality of the catalogs was assessed in detail using statistical parameters and a new formula for the location quality. The completeness magnitude of the new catalogs is as low as 0.82. The noise affecting the network was also evaluated. This study confirms the importance of the OT local network for seismic hazard analysis and provides a useful dataset for seismotectonic and geophysical studies in a long under-monitored region.