A revised image of the instrumental seismicity in the Lodi area (Po Plain, Italy)

Abstract. We analysed the instrumental seismicity in a sector of Po Plain (Italy) to define baseline for seismic monitoring new underground gas storage plant that will use depleted reservoir Cornegliano Laudense, near Lodi. The target area – square approximately 80 km × wide is commonly considered aseismic. period, 1951–2019, includes all available data. gathered P- and S-phase readings collected by various agencies more than 300 events, located inside area. processed earthquakes uniformly, using absolute location algorithms velocity models adopted regional national networks. relocated earthquake dataset depicts an image weak deep this central Plain, which quite different from initial one derived existing catalogues. Within distance 30 Lodi, are extremely rare (on average 0.5 per year, assuming completeness magnitude Mc = 2.7 1980s); only two events fall at less 15 whole period 1951–2019. strongest instrumentally recorded related sequence Caviaga 1951 represent first recordings Confirming hypocentral depths recently proposed Caciagli et al. (2015), far reservoir; we suggest common tectonic stress main shock M4.2 17 December 2020, based on similarities depth, location, focal mechanism. While it clear corresponds collision between Northern Apennines Southern Alps, characterization geological structures generate appears uncertain. Our results preliminary benchmark definition seismogenic zones Lodi area, whose can be improved with observational capabilities now surroundings.