GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 We used about 400 local earthquakes as templates and we applied template-matching detection algorithms to a 13-month-long dense passive survey. We obtained a final double-difference catalogue of 5,070 earthquakes (-0.7<M L <2.6; M C =0.1). The new catalogue allows precisely tracking the spatiotemporal distribution of the swarm-seismicity and to map the b-value of the Gutenberg-Richter law. We combine seismicity data with available subsurface geophysical data, fostering an improved interpretation of the RIS. Space-time earthquake distribution clearly shows that seismicity is organised in four distinct clusters, indicating a progressive southward activation in response to loading/unloading phases of the Pertusillo reservoir. Seismicity unravels new km-scale faults and/or better defines faults partially-illuminated by the previously available earthquake catalogues. All earthquakes are confined within a brine-saturated fractured carbonate reservoir, reactivating with extensional kinematics pre-existing reverse/transpressional faults favourably oriented in the present-day extension. In particular, seismicity is strongly controlled by inherited hydromechanical rock properties (i.e., rock fracturing; geometry of inherited faults; pore-fluid-pressure). In agreement with these observations, b-value shows a significant spatial variability, with very-high b-value (up to 2.2) within areas of distributed seismicity, while lower (~1.2) b-value associated with on-fault larger magnitude seismicity. All observations suggest that a poroelastic stress transmission mechanism, due to the seasonal water level oscillation, can explain the Pertusillo RIS. References Bello, S., Lavecchia, G., Andrenacci, C. et al. (2022). Complex trans-ridge normal faults controlling large earthquakes. Sci. Rep. 12, 10676. https://doi.org/10.1038/s41598-022-14406-4 . DISS Working Group (2010). http://diss.rm.ingv.it/diss/, doi: 10.6092 /INGV.IT -DISS3.1.1. Gupta H. K. (2002). A review of recent studies of triggered earthquakes by artificial water reservoirs with special emphasis on earthquakes in Konya, India. Earth-Science Reviews, 58 . Improta L., Ferranti L., De Martini PM, Piscitelli S., Bruno PP, Burrato P., Civico R., Giocoli A., Iorio M., D’Addezio G., Maschio L. (2010). Detecting young, slow-slipping active faults by geologic and multidisciplinary high-resolution geophysical investigations: a case study from the Apennine seismic belt, Italy. Journal of Geophysical Research: Solid Earth 115(B11). https://doi.org/10.1029/2010JB000871 . Improta L., Valoroso L., Piccinini D., Chiarabba C. (2015). A detailed analysis of wastewater induced seismicity in the Val d’Agri oil field (Italy). Geophysical Research Letters. https://doi.org/10.1002/2015GL063369 .