An Enhanced Catalog of Repeating Earthquakes on the 1980 Irpinia Fault System, Southern Italy

Abstract

A pilot study employing a template-matching approach on the detection of repeating earthquakes (or repeaters) in a small volume of the Irpinia fault (Southern Italy) is presented here. A catalog of repeaters nucleating over about a decade with local magnitudes ranging between ML 0.4 and ML 1.7 is generated. The events nucleate at depths of about 11 km over a fault patch with a size of about 600 m. Assuming a constant stress drop for all repeaters, the yearly coseismic slip rate of the patch is estimated in the range of 1–4.8 mm with a mean value of about 3.4 mm, which is close to the fault slip rate estimated by geodetic approaches. Given the mechanical properties of the medium in the source region of the repeaters revealed by previous tomographic studies, and in particular the high Vp/Vs ratio (close to 1.95), it is postulated that these events are fluid triggered, consistently with the mechanism proposed for the generation of most of the microseismicity in the area. The encouraging outcomes of this study suggest to focus future measurement campaigns on this area and open perspectives to extend this approach to other segments of the Irpinia fault to reveal small-scale frictional properties in an area capable to generate M7 earthquakes.

Remobilization of Inverted Normal Faults Drives Active Extension in the Axial Zone of the Southern Apennines Mountain Belt (Italy)

“…During the last four decades, a moderate aftershock and background seismicity has continuously affected the crustal volume delimited by the faults that were activated during the 1980 M S 6.9 Irpinia earthquake (e.g., De Matteis et al, 2012;Amoroso et al, 2014). Furthermore, since 2005, the monitoring of the Irpinia region by dense seismic networks (Irpinia Seismic Network, ISNet, and the Istituto Nazionale di Geofisica e Vulcanologia network, INGV) revealed the occurrence of persistent seismicity with magnitude near 0 (De Landro et al, 2015;Amoroso et al 2017;D'Agostino et al 2018;Festa et al 2021;Picozzi et al 2019;Palo et al 2023aPalo et al , 2023b.…”