GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Seismic cycle in bituminous dolostones (Central Apennines, Italy) M. Chinello 1 , E. Bersan, M. Fondriest 1 , T. Tesei 1 , G. Di Toro 1,2 1 Dipartmento di Geoscienze, Università degli studi di Padova, Padua, Italy 2 Isttuto Nazionale di Geofsica e Vulcanologia (INGV), Rome, Italy Central Apennines in Italy is one of the most seismically actve areas in the Mediterranean (e.g., L’Aquila 2009, Mw 6.3 earthquake), with mainshocks and afershocks propagatng along extensional faults cutng km-thick sequences of carbonates. As a consequence, fault rock assemblages may record the seismic cycle under a wide range of loading conditons, temperatures, and fuid-rock interactons that actvates several mechanical and chemical processes (i.e., fracturing, crystal-plastc deformaton, dissoluton and precipitaton). We document the interplay between these deformaton mechanisms in normal faults cutng through bituminous dolostones in the Central Apennines. We sampled faults with increasing displacement (from 1-2 mm to a few meters) and with ultra-polished slip surfaces (“mirror-like surface”). Microstructural analysis of the slip zones show evidence of cataclasis, pressure soluton and smearing of bitumen. Furthermore, the fault surfaces with higher displacement also record multple slip events with ingression of carbonate-rich fuids and fragments of older slip zones sealed by calcite precipitaton. Sometmes, these fragments derive from bitumen-rich slip zones with evidence of viscous fow. We propose that these microstructures preserve the evidence of multple cycles of: high strain rate coseismic embritlement (i.e., fragments of previous slip zones associated to fuid ingression), long-term aseismic or post-seismic creep (i.e., bitumen viscous fow and pressure soluton) and fault locking/sealing (i.e., calcite precipitaton). Since mirror-like surfaces can form both during seismic slip (Fondriest et al., 2013; Siman-Tov et al., 2015; Ohl et al., 2020; Pozzi et al., 2018) and aseismic creep (Tesei et al., 2017; Verbene et al., 2013), this study presents a natural case of diferent processes actng in the same slip zones throughout the seismic cycle. References Fondriest, M. et al.; 2013: Mirror-like faults and power dissipaton during earthquakes. Geology 41, 1175–1178. Ohl, M. et al.; 2020: Mechanisms of fault mirror formaton and fault healing in carbonate rocks. Earth Planet. Sci. Let. 530, 115886. Pozzi, G., et al; 2018: A new interpretaton for the nature and signifcance of mirror-like surfaces in experimental carbonate-hosted seismic faults. Geology 46, 583–586.