GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Earthquake catalog enhancement through template matching: an application to the Southern Apennines (Italy) G. Diaferia 1 , L. Valoroso 1 , D. Piccinini 2 , L. Improta 1 1 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Nazionale Terremoti, Roma 2 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa Improving the capability of seismic networks to detect small-magnitude seismicity, commonly near or below the detectability threshold, is the prerequisite to characterize the seismotectonics of an area in terms of fault geometry, kinematics and mechanics, thus leading to an improved comprehension on the physical mechanisms that generate small and large earthquakes. In this work, we apply template-matching , a cross-correlation based technique for the detection of hidden earthquakes, at the scale of the Southern Apennines (Italy). Here, the ongoing extension of the Mio-Pliocene Apennine thrust-belt poses a major seismic hazard, as testified by several Mw~7 earthquakes that struck this area in the past 300 years. No clear consensus exists on the seismotectonic models related to such events, particularly in terms of characterization of the fault structure and crustal rheology that can thus largely benefit from the application of template-matching . As template events, we use ~4000 earthquakes occurring between 2009 and 2015, recorded by 181 stations from the INGV National Seismic Network. We scan six years (2009-2015) of continuous recordings with the template-matching algorithm, ending up with ~3 million (possible) detections. Only 3% (~88.000 events) comply with the minimum quality thresholds that we set (at least four P and four S picks, recorded at least at five stations). For determining earthquake locations we used the fully-probabilistic non-linear code NonLinLoc, with an ad-hoc 1D velocity model and corrections for station residuals. By accounting for the quality of the hypocenter location, the final catalog comprises ~26.000 new seismic events, showing a mean horizontal and vertical error of 1.5 and 2.8 km, respectively, and a mean RMS of 0.14 s. These values are only slightly higher than those of the template catalog, mainly due to the lower number of phase arrivals that usually constrain the detected events. Given the small magnitude (M L <1) of the majority of the newly detected events, the new catalog shows a decrease in magnitude of completeness from 1.6 to 0.5 or 0.6 using the Max-curvature or the MC90 methods, respectively. The main NW-SE trending seismogenic structures of the axial zone of the chain are illuminated by abundant microseismicity, with evident gaps delineating the along-strike boundary of such