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 properties of faults and fault systems. In this study, we provided detailed location and characterization of events of the 3-7 July 2020 Irpinia sequence (southern Italy) that occurred at the northern tip of the main 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 focal mechanisms determination for the largest quality events. We found that the sequence ruptured an asperity with a size of about 800 m, along a fault structure having a strike compatible with the one of the main segments of the 1980 Irpinia earthquake, and a dip of 50-55 degrees at depth of 10.5-12 km and 60-65 degrees at shallower depths (7.5-9 km). Low stress drop release (average of 0.64 MPa) indicates a fluid-driven initiation mechanism of the sequence. We also evaluated the performance of the earthquake early warning systems running in real-time during the sequence, retrieving a minimum size for the blind zone in the area of about 15 km.

Automated summary

The study provided detailed location and characterization of events of the 2020 Irpinia seismic sequence, showing that the sequence ruptured an asperity with a size of about 800 m along a fault structure compatible with the main segment of the 1980 Irpinia earthquake, with low stress drop indicating a fluid-driven initiation mechanism. The performance of earthquake early warning systems during the sequence was evaluated, revealing a minimum blind zone size of about 15 km in the area.