Study of the microstructures and mineralogical phases in the fault gouge and their relationship with the fault seismicity, a case study of the Astaneh fault

Abstract:The Astaneh Fault is one of the active and seismic faults in the Shahroud sinistral fault system. Fault gouges can be seen in a completely pristine and unchanged form in the portions of this fault that have affected the carbonate rocks. Fault gouges are the direct product of lithology and are formed as a result of the fault slip from the host rocks. Studying these rocks for type, composition, mineralogical phases and structure can provide results on how the fault slip and gouge process occurs. The result of a seismic slip in faults, and especially in gouges, are different types of deformations, such as mineralogical and compositional deformations, depending on the conditions of their formation. From this deformation model, we can mention the thermal decomposition of calcite and dolomite, as well as the presence of siderite in gouges. In this article, by studying the combined [aggregated] microstructures in the Astaneh fault gouge, their relationship with seismic slip has been investigated. According to previous research, the Astaneh Fault is certainly a seismic fault. The presence of the resulting thermal decomposition of calcite and dolomite (calcium and magnesium oxide or periclase) and the welding of particles due to heat may be the key to seismic slip in this fault.