5:15 PM - 6:45 PM
[SSS05-P20] Frictional properties of brittle fault zone: insights from low- to high-velocity rotary shear experiments on sandstone gouges within Main Frontal Thrust, Himalaya
Keywords:fault friction, crustal deformation, Main Himalayan Thrust, Main Frontal Thrust, seismic nucleation
These crustal-scale faults are the area of stress accumulation and their eventual release as a result of ongoing deformation. The stress release mechanism defines if the process will be instantaneous leading to an earthquake, or it can be infinitesimally slow leading to aseismic creep. In case of crustal faults, factors like pre-existing weak planes, and heterogeneity in fault rocks affect the stress release mechanisms. Therefore, frictional properties of heterogenous fault rocks from brittle deformation zone help elucidate development of shallow crustal earthquakes of creep mechanisms.
The Main Himalayan Thrust is considered the crustal-scale fault boundary between the subduction margin of the Indian-plate below the Eurasian-plate. The Himalayan Frontal Thrust represents the shallow crustal portion (2–5 Km depth) of this active Indo-Eurasian subduction margin. The present research is aimed to elucidate the effects of constituent mineral heterogeneity on the frictional properties of protoliths and fault gouges within the Himalayan Frontal Thrust.
The present convergence rates along the active Indo-Eurasian subduction margin varies longitudinally from west to east, with a mean convergence rate estimated ~15 mm/year. This continuing northward subduction of the Indian Plate results in stress accumulation along the Main Himalayan Thrust. However, historically the number of large earthquakes (> M5) are conspicuously low in the Himalayan region, representing a major deficit in stress release events. The present study area within the Main Frontal Thrust exhibit sandstone protoliths with varying phyllosilicate content and brittle fault zone exhibiting gouges with cataclastic and foliated microstructural features. Pressurized rotary-shear velocity step experiments at slow velocities (10–200 µm/s; creep), and fast velocity (1.5 m/s; seismic) were conducted on powdered protolith and fault zone rocks. All the experiments were conducted in wet condition (maintaining pore pressure) under 10 MPa effective normal stress condition. The mechanical data from the deformation experiments and microstructures of recovered samples provide insights on weakening mechanisms of the fault rocks and controls on seismic nucleation in the Himalayas.
The Main Himalayan Thrust is considered the crustal-scale fault boundary between the subduction margin of the Indian-plate below the Eurasian-plate. The Himalayan Frontal Thrust represents the shallow crustal portion (2–5 Km depth) of this active Indo-Eurasian subduction margin. The present research is aimed to elucidate the effects of constituent mineral heterogeneity on the frictional properties of protoliths and fault gouges within the Himalayan Frontal Thrust.
The present convergence rates along the active Indo-Eurasian subduction margin varies longitudinally from west to east, with a mean convergence rate estimated ~15 mm/year. This continuing northward subduction of the Indian Plate results in stress accumulation along the Main Himalayan Thrust. However, historically the number of large earthquakes (> M5) are conspicuously low in the Himalayan region, representing a major deficit in stress release events. The present study area within the Main Frontal Thrust exhibit sandstone protoliths with varying phyllosilicate content and brittle fault zone exhibiting gouges with cataclastic and foliated microstructural features. Pressurized rotary-shear velocity step experiments at slow velocities (10–200 µm/s; creep), and fast velocity (1.5 m/s; seismic) were conducted on powdered protolith and fault zone rocks. All the experiments were conducted in wet condition (maintaining pore pressure) under 10 MPa effective normal stress condition. The mechanical data from the deformation experiments and microstructures of recovered samples provide insights on weakening mechanisms of the fault rocks and controls on seismic nucleation in the Himalayas.