A recent, low-magnitude seismic sequence in the epicentral area of Ms 6.9, 1980 Irpinia earthquake

The 1980 Irpinia earthquake was the most destructive, instrumental earthquake of Southern Apennines, occurred along NW-SE trending normal faults. A complex rupture process involved multiple fault segments according to (at least) three different nucleation episodes producing ∼ 3000 fatalities, ∼ 9000 injured, and up to 280,000 displaced people. Several models, characterized by different number, geometries and locations of activated fault segments, have been proposed by different authors to explain the complex rupture that originated the Irpinia earthquake (Bernard and Zollo, 1989 and references therein). 42 years later, some questions about the number and the location of seismogenic sources of the region are still open within the scientific community, despite recent studies have been published (Adinolfi et al., 2020; Festa et al., 2021; Bello et al., 2021). This work proposes a detailed study of a small seismic sequence (ML 3.7 mainshock) that occurred in March 2012 in the proximity of a specially interesting zone, the so called “Sele Gap”, which remained inactive during the Irpinia 1980 earthquake. Despite the limited number of small magnitude events, the analyzed microseismic sequence was highly space-time clustered and can be a powerful tool to investigate the activated fault segment in terms of geometry, kinematics or depth extension within the seismogenic layer of the Irpinia area. Our preliminary results, based on the earthquake re-locations and focal mechanisms, show the activation, during the 2012 sequence, of a fault located near the Marzano-Cervialto normal fault segments, which have been interpreted as two strong asperities, activated during the 1980 Irpinia earthquake and separated by the low-strength zone, Sele (“relaxation”) barrier (Bernard and Zollo, 1989). Our analysis contributes to further studying the Irpinia, low-magnitude instrumental seismicity, and to better define the fault segmentation pattern of the seismogenic structures of the area.