The Microstructural Characteristics of Fault Rocks from the Wasatch Fault Zone in Utah (USA) Under Polarizing and Electronic Microscope and Its Seismogeologic Significance

摘要

The microstructures of fault rocks from the Wasatch fault zone in Utah （USA） have been studied using a polarizing microscope,a scanning electron microscope （SEM） and an ultrahigh-voltage electron microscope （HVHM）.This fault zone may be recognized as one a with long history of seismic activity according to the microstructural characteristics such as type, deformation characteristics,melting structure and surface textures of the fault rocks.However,the main fault now present seems not to have been noticeably active since the late Pleistocene （Q₃）,as shown by the eroded-surface texture on the quartz fragments in the fault gouge.Meanwhile,those faults supposed to be strongly active in modern times are branching faults much closer to the basin side and are covered by the Holocene sediments in the basin.