Seismic Cycle in Bituminous Dolostones (Monte Camicia Thrust Zone, Central Apennines, Italy)

Abstract

AbstractSeismic ruptures often propagate along fault zones cutting km‐thick sequences of carbonates (e.g., Wenchuan Mw 7.8, 2008, China; L’Aquila Mw 6.1, 2009, Italy). As a consequence, fault rock assemblages may record the seismic cycle under a wide range of loading conditions, temperatures (>1,000°C during co‐seismic slip), and fluid‐rock interactions. The Monte Camicia Thrust Zone in the Italian Central Apennines is exhumed from ∼3 km depth. We studied the seismic cycle recorded by a network of faults cutting bituminous dolostones in the footwall of the Monte Camicia Thrust. These faults accommodate up to several meters of displacement. Slip zones are mm‐ to cm‐thick and bounded by ultra‐polished (“mirror‐like”) surfaces independently of their displacement. At the microscale, deformation is accommodated by cataclasis and pressure‐solution in carbonates, and viscous flow in the foliated bitumen. Some of the faults with displacements >0.10 m have multiple slip zones, separated by “mirror‐like” surfaces, and include clasts of foliated bitumen and fragments of older slip zones sealed by calcite precipitation. We conclude that (a) slip zones record post‐ to inter‐seismic (foliated bitumen) and co‐seismic (fragments of bitumen) deformation in a fluid‐rich environment (calcite precipitation) and (b) mirror‐like surfaces formed during all phases of the seismic cycle.