Research On The Characteristics Of Active Fault Gouges At The Nano/Micro Scale

Since the eighties of the 20 th century, the study of fault gouges in fault zone has garnered attention. The mainly research directions include study of quartz grains microstructure characteristics of gouges, study of mineral composition of gouges, study of physical and mechanical properties determination of gouges, study of grain size distribution of gouges, study of fractal characteristics of gouges, study of the age determination of the formation(thermal luminescence, K-Ar dating, Raman spectroscopy) and study of microstructural features of gouges. With the wide application of scanning electron microscope(SEM), the writers tried to study on the components deformation characteristics of the scratches on the principle sliding zone(PSZ,or named the a-b fabric plane in this paper) and the foliation belt outside the PSZ(named the a-c fabric plane in this paper) at the nano/micro scale.Tanlu fault zone is an important deep fault belt in eastern China, north from the Guangji area, extending across Anhui, Jiangsu, Shandong, Bohai Bay and three provinces in the northeast of China, to enter the territory of Russia. The section located in Shandong and Jiangsu is the Yishu fault zone, earthquake activity of which is the strongest. Especially, the Juxian-Anqiu fault, which is a Holocene active fault, is a typical representative. Since the seventies of the 20 th century, through there has been a lot of research results on Quaternary activity and seismic activity of Yishu fault zone and preliminary observation of the microscopic structure of fault gouges has been carried out, research on fault gouges at the nano/micro scale is still blank.This paper is based on the gouges in Yishu fault zone and the north-east or north-west active faults on both sides of which as the research object, involving 7 faults and 123 samples collected. The writers used SEM to observe clay minerals deformation styles of gouges. Then they analysis and summarize the deformation characteristics and significance. The main understandings and achievements obtained are shown as follows:(1) Contrast experiment: the micro samples were made of gouges which was obtained from gouges by dissolution, deposition and dry and clay with obvious scratches which were corrected from drilling. The samples were observed, compared and analyzed. At the nano/micro scale, the clay minerals made by natural sedimentation experiment are randomly arranged, and the clay minerals of fault gouges are arranged in order. Slickensides of fault gouges on the a-b fabric plane are featured with flat and sliding quickly, which belongs to seismic structure; on the contrary, slickensides of drilling micro samples on the a-b fabric plane is crooked and wave-like and shows the feature of sliding slowly, which belongs to non-seismic structure.(2) Nano/micro characteristics on the PSZ: the phenomenon of different directions scratches on the PSZ may be caused by multiple active fault. According to the relationship between cross striation of slickensides, the stress direction can be determined which occurs earlier, so that the regional stress change process can be known. In addition, multiple scratches may also be formed by the same earthquake with the main shock and aftershocks. There are some epigenetic minerals on the a-b fabric plane of gouges in some sections. According to these minerals, the relationship between fault activity can be roughly distinguished.(3) Stick slipping and creep slipping: on the basis of macroscopic investigation and previous research data, from macro and micro to ultra micro, the marks of stick slipping and creep slipping were summarized according to the characteristics of the nano/micro deformation of gouges. Stick slipping is characteristic of scratches, slickenside, grinding ridges, grinding grooves and steps. Creep slipping is characteristic of fold deformation of flake clay minerals, clay mineral slipping around gravels, exfoliation structure of flake clay minerals and wave arrangement of flake clay minerals.(4) According to the research on deformation characteristics of gouges at the nano/micro scale, seismogenic mode is established initially and earthquake generation system can be divided into two tectonic units-earthquake cultivation unit and earthquake occurrence unit. It is considered that the creep slipping before main shock is of significance for earthquake prediction. And the aspect study of gouges is provided with micro geological evidence for the feasibility of earthquake prediction.