Insights into Mechanical Properties of the 1980 Irpinia Fault System from the Analysis of a Seismic Sequence

Seismic sequences are a powerful tool to locally infer geometrical and mechanical propertiesof faults and fault systems. In this study, we provided detailed location and characterization ofevents of the 3–7 July 2020 Irpinia sequence (southern Italy) that occurred at the northern tip of themain segment that ruptured during the 1980 Irpinia earthquake. Using an autocorrelation technique,we detected more than 340 events within the sequence, with local magnitude ranging between−0.5 and 3.0. We thus provided double difference locations, source parameter estimation, and focalmechanisms determination for the largest quality events. We found that the sequence ruptured anasperity with a size of about 800 m, along a fault structure having a strike compatible with the oneof the main segments of the 1980 Irpinia earthquake, and a dip of 50–55◦ at depth of 10.5–12 kmand 60–65◦ at shallower depths (7.5–9 km). Low stress drop release (average of 0.64 MPa) indicatesa fluid-driven initiation mechanism of the sequence. We also evaluated the performance of theearthquake early warning systems running in real-time during the sequence, retrieving a minimumsize for the blind zone in the area of about 15 km.