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

Abstract

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° at depth of 10.5–12 km and 60–65° 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.

Decade-long monitoring of seismic velocity changes at the Irpinia fault system (southern Italy) reveals pore pressure pulsations

“…The catalogue of micro-seismicity shows a stable low magnitude (0.5 < M L < 3.5) pattern, which is spatially located along the whole system, is widespread inside the volume between the boundary faults (i.e., southwest and northeast boundary faults in Fig. 1 b, referred to as SWBF and NEBF, respectively 12 ), and allows an investigation of the interaction processes between crustal fluids and micro-seismicity at the IFS with different approaches 13 .…”

The Near Fault Observatory community in Europe: a new resource for faulting and hazard studies

“…This area undergoes an extensional rate of ~3 mm/yr, as inferred from geodetic measurements [D'Agostino et al, 2010]. Present-day low-magnitude seismicity (M < 3.5) occurs in the shallow portion of the crust, is organized in seismic sequences [Festa et al, 2021] and appears spread into a large, fractured volume confined in the graben responsible for the 1980 earthquake. Beyond the large seismic hazard of the area, the main scientific questions targeted by this infrastructure is to understand the role of fluid-rock interaction and fluid diffusionwater and carbon dioxide [Amoruso et al, 2014], in the production of the earthquakes, and the contribution of the charging process of shallow aquifers in affecting the stress of rocks at seismogenic depths [D'Agostino et al, 2018].…”

“…Today, CREW compares the EEW software PRESTo [Satriano et al, 2011] and VS -Virtual Seismologist [Behr et al, 2016], on the real time data streaming from ISNet [Festa et al, 2021]. Each virtual guest has been assigned the same amount of (virtual) hardware resources, so that its final performances will only depend on the EEW software algorithms and configuration, given the availability of the same set of recorded waveform data in a timely fashion.…”

Microseismicity Monitoring and Site Characterization With Distributed Acoustic Sensing (DAS): The Case of the Irpinia Fault System (Southern Italy)

“…The Irpinia Near Fault Observatory (INFO) monitors the area that experienced the M 6.9, 1980 Irpinia earthquake, the strongest and most destructive seismic event of the last decades in Italy (Rovida et al, 2019). The present-day seismicity is mainly confined to the graben delimited by the main fault segments of the 1980 earthquake and is characterized by several swarm-like microearthquake sequences (Festa et al, 2021;Stabile et al, 2012). Velocity and attenuation tomographic images show an anomaly corresponding to earthquake locations (low vs., high vp-to-vs; high Qp), indicating the presence of fluids, eventually with a mixture brine-CO 2 and/or CH 4 -CO 2 (Amoroso et al, 2014(Amoroso et al, , 2017Vassallo et al, 2016).…”