Preprints
https://doi.org/10.5194/se-2021-35
https://doi.org/10.5194/se-2021-35

  15 Apr 2021

15 Apr 2021

Review status: this preprint is currently under review for the journal SE.

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

Laura Peruzza1, Alessandra Schibuola1,2, Maria Adelaide Romano1, Marco Garbin1, Mariangela Guidarelli1, Denis Sandron1, and Enrico Priolo1 Laura Peruzza et al.
  • 1OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Sgonico (TS), 34010, Italy
  • 2Dipartimento di Matematica e Geoscienze, Università degli Studi di Trieste, Trieste, 34100, Italy

Abstract. We analyse the instrumental seismicity in a sector of the Po Plain (Italy) with the aim of defining the baseline for seismic monitoring of a new underground gas storage plant that will use the depleted gas reservoir of Cornegliano Laudense, near Lodi. The target area – a square approximately 80 x 80 km wide – is commonly considered aseismic. The analysed period, 1951–2019, includes all available instrumental data. We gathered the P- and S-phase readings collected by various agencies for more than 300 events, approximately located inside the target area. We processed the earthquakes in a uniform way, using absolute location algorithms and velocity models adopted by the regional and national monitoring networks. The relocated earthquake dataset depicts an image of weak and deep seismicity for this central sector of the Po Plain, which is quite different from the initial one derived from the existing earthquake catalogues. Within a distance of approximately 30 km from Lodi, earthquakes are extremely rare (on average 0.5 earthquake/yr, assuming a completeness magnitude Mc = 2.7 from the 1980s); only 2 weak events fall at less than 15 km distance from the reservoir in the whole period 1951–2019. The strongest events instrumentally recorded are related to the seismic sequence of Caviaga in 1951 that represent the first instrumental recordings for that area. Confirming the hypocentral depths recently proposed by Caciagli et al., 2015, the events are far from the gas reservoir; we suggest a common tectonic stress of the main shock of 1951 and the M4.2 earthquake of Dec 17, 2020, on the basis of the similarities in depth, location and focal mechanism. While it is clear that the deep seismicity corresponds to the collision between the Northern Apennine and Southern Alps, it is much less clear, however, which geological structures are capable of generating earthquakes. Our results and the improvement in the observational capabilities of the very last years will help refining the seismogenic sources hypothesized for this area.

Laura Peruzza et al.

Status: open (until 04 Jun 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2021-35', Anonymous Referee #1, 26 Apr 2021 reply
  • RC2: 'Comment on se-2021-35', Anonymous Referee #2, 26 Apr 2021 reply

Laura Peruzza et al.

Laura Peruzza et al.

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Short summary
In weakly seismic or poorly monitored areas, the uncritical use of earthquake catalogues can be misleading. This is the case of a central sector in the Po Valley, where Northern Apennine and Southern Alps collide. We collect and reprocess the available instrumental data of about 300 earthquakes from 1951 to 2019. The seismicity is weak and deeper than expected, and far from some existing human activities carried on in the underground. The potential tectonic causative sources are still unknown.