Fault geometry and mechanics of marly carbonate multilayers: An integrated field and laboratory study from the Northern Apennines,Italy |
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| Institution: | 1. Dipartimento di Scienze della Terra, Università degli Studi La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy;3. Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, Via Alessandro Pascoli, 06123 Perugia, Italy;1. Computational Geology Laboratory, Polish Geological Institute – National Research Institute, Wroc?aw, Poland;2. Physics of Geological Processes, University of Oslo, Norway;1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, China;2. HPT Laboratory, Department of Earth Sciences, Utrecht University, The Netherlands;1. Dept. Geosciences, Penn. State Univ., University Park, PA, United States;2. Dept. Earth Sciences, UC Santa Cruz, Santa Cruz, CA, United States |
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| Abstract: | Sealing layers are often represented by sedimentary sequences characterized by alternating strong and weak lithologies. When involved in faulting processes, these mechanically heterogeneous multilayers develop complex fault geometries. Here we investigate fault initiation and evolution within a mechanical multilayer by integrating field observations and rock deformation experiments. Faults initiate with a staircase trajectory that partially reflects the mechanical properties of the involved lithologies, as suggested by our deformation experiments. However, some faults initiating at low angles in calcite-rich layers (θi = 5°–20°) and at high angles in clay-rich layers (θi = 45°–86°) indicate the important role of structural inheritance at the onset of faulting. With increasing displacement, faults develop well-organized fault cores characterized by a marly, foliated matrix embedding fragments of limestone. The angles of fault reactivation, which concentrate between 30° and 60°, are consistent with the low friction coefficient measured during our experiments on marls (μs = 0.39), indicating that clay minerals exert a main control on fault mechanics. Moreover, our integrated analysis suggests that fracturing and faulting are the main mechanisms allowing fluid circulation within the low-permeability multilayer, and that its sealing integrity can be compromised only by the activity of larger faults cutting across its entire thickness. |
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| Keywords: | Mechanical multilayer Northern Apennines Fault Rock mechanics |
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