Principal Slip Zones in Limestone: Microstructural Characterization and Implications for the Seismic Cycle (Tre Monti Fault, Central Apennines, Italy)

摘要: Earthquakes in central Italy, and other areas worldwide, often nucleate within rupture through carbonates the upper crust. During individual earthquake ruptures, most fault displacement is thought to be accommodated by thin principal slip zones. This study presents detailed microstructural observations of zones seismically active Tre Monti normal zone. All cut limestone, geological constraints indicate exhumation from \2 km depth, where ambient tempera- tures are � 100C. Scanning electron microscope suggest that composed 100% calcite. The secondary faults damage zone contain protocata- clastic cataclastic fabrics cross-cut systematic fracture networks stylolite dissolution surfaces. has much more complexity, contains a 2-10 mm thick ultracataclasite lies immediately beneath surface. itself internally zoned; 200-300 lm-thick ultracataclastic sub-layers record extreme localization slip. Syn-tectonic calcite vein net- works spatially associated with fluid involvement faulting. preserve compelling evidence fluidization, also con- tain peculiar rounded grains consisting (often angular) clast wrapped laminated outer cortex ultra-fine-grained These ''clast-cortex grains'' closely resemble those pro- duced during layer fluidization settings, including basal detachments catastrophic landslides saturated high-velocity friction experiments on clay-bearing gouges. An overprinting foliation present fault, backscatter diffraction analyses presence weak crystallographic preferred orientation (CPO) fine-grained matrix. c-axes systematically inclined direction shear. We ultra- formation clast-cortex occurred at high strain rates propa- gation seismic ruptures whereas development an CPO intergranular pressure solution post-seis- mic creep. Further work required document range microstructures localized different lithologies, compare natural produced controlled deformation experiments.