GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Are productve gas felds antcorrelated with large seismogenic faults? Implicatons for hydrocarbon exploitaton and seismic hazard G. Valensise 1 , F. Donda 2 , A. Tamaro 2 , S. Parolai 3 1 INGV, Rome, Italy 2 OGS, Trieste, Italy 3 University of Trieste, Italy Thrust faultng earthquakes are an inherent occurrence in hydrocarbon-bearing actve regions dominated by crustal shortening: they may be generated by regional-scale tectonic processes, but also triggered at all stages of hydrocarbon exploitaton actvites. Their occurrence, however, is highly heterogeneous, as earthquakes ofen appear scatered across relatvely homogeneous tectonic trends. For instance, investgatons of the seismicity of the Zagros region (southern Iran: Nissen et al., 2011), one of the largest oil and gas reserves worldwide, revealed (a) that thrust faultng earthquakes are less frequent than strike-slip events, despite the characteristc and actvely deforming fold-and-thrust structure of the region; and, more importantly, that (b) the observed seismicity accounts for a small fracton of the region’s shortening estmated from geodetc observatons. In a frictonal regime, the fracton of fault slip that is released in earthquakes is generally referred to as seismic coupling, or c , a dimensionless parameter introduced in the 1970s based on observatons of great earthquakes of the circum-Pacifc belt (Kanamori et al., 1971). Investgatons of the compressional domains encircling the Italian peninsula, most of which host important oil and gas reservoirs, have already suggested that the average c is about 50% (Carafa et al., 2017); half than that estmated for the extensional domains straddling the Apennines chain, which is close to 1.0. Is this the result of episodically aseismic behaviour of the large thrust faults occurring beneath Italy’s hydrocarbon reservoirs? How else could it be exaplained? These questons were initally addressed by Mucciarelli et al. (2015), moving from the evidence ofered by the 20 and 29 May 2012, M w 5.9-6.0, Emilia earthquakes. These workers focused on the 2D spatal relatonships between some known seismogenic sources supplied by the DISS database (DISS Working Group, 2021), and the distributon of 455 gas felds falling in a ∼ 10,000 km 2 porton of the central-southern Po Plain, using data supplied by the “Visibility of Petroleum Exploraton Data in Italy” (ViDEPI) database run by the Italian Ministry of Economic Development ( htps:// www.videpi. com/videpi/pozzi/pozzi.asp ). Based on this exercise, they proposed the existence of an antcorrelaton between productve reservoirs and the presence of relatvely large seismogenic faults, i.e., faults capable of M w 5.5 + earthquakes.