Dongjiang Reservoir is located in southeastern part of Hunan Province, South China. The dam is 157m high. The capacity of the Reservoir is about 81.2 × 10⁸m³.Since August of 1986,it started to storage water,several thousands of induced earthquakes were recorded by the arrayof micro-seismic stations from November of 1987 to December of 1993, the maximum events of M_L＝3.0 occurred on 24 July,1989,and of M_L＝3.2, on 2 July,1990.Based on the research-es of regional geology,activity of the main fault zones,tectonic karstification by using the deter-mination and integrated analysis of time of fault activity, fabric characteristics, microstructures,structural joints,karstification and stress field, it could be suaggersted that there is no direct re-lationship between the occurrence of induced earthquake and the activity of the main fault zonesin the reservoir area. The distribution of induced earthquakes are confined in the area with kars-tificated strata and the complex weak zone with combination of multple structures. The authorsconsider that the percolation pressure can increase with the uprising level of storage water in thereservoir, and the induced earthquake will occur by the small fracturing or resliping along someweak plane or zone caused by the local stress adjustment. The induced earthquake activity willdeduce with the balance of local stress adjustment and the level of storage water in the reservoir.The maximum magnitude of induced earthquake in Dongjiang Reservoir will be below M_L＝4.0.

Sructural joints and gouges of the main fault zones in Northern North China were determined,statistically studied and analysed on micro-computer and scanning electron microscopy(SEM). Only twenty percents of the structural joints are oriented in the direction favorable to activation in the effect of the present stress field. Most of these structural joints were formed in the local stress field associated with the formation of the fault zones. The statistical study of rnicro-textures on the surface of quartz fragments from the fault gouges on SEM gives the last activity time of these fault zones, and the SEM determination of microstructures provides some information on the movernent mode along these fault zones. The results of these methods will provide more evidence for the fault activity.

The experimental study on transient processes of fracture and stick-stip instability shows that both of the stress drop and the displacement rise are not monotonous.They are oscillatory ones with multifrequencies.The SEM observation on fracture surfaces shows that the oscillation led to bilateral or multilateral traces.By combining the experimental results with the phenomena observed from natural fault surface and fault zone,such as slickensides,grooving,steps and abnormal array of subfaults,it has been presented that one of the reasons for the traces which reflect the bilateral or multilateral motions of natural fault may be the instability oscillation of fault from an event (earthquake).In contrast,these phenomena may be indicators as ancient earthquakes.

Some Scanning Electron Microscopy (SEM) microtextures have been observed on the products of quartzite from triaxial compression experiments with a confining pressure of 1-5 Kb and a strain rate of 4.4?10^-5/sec.The SEM microtextures resulting from stick-slip are distinguishable from those resulting from steady-state slip.The former shows the characteristics of bashing and shearing fracture or rapid slipping,and the latter demonstrates those associated with rubbing fracture and slow shearing.The SEM mic-rotextures in products from active faults can be compared with those from experiments.It is significant to distinguish between stick-slip and steady-state slip motion of active iaults by using these typical SEM microtextures.

The study of products from active fault has been concened by seismogeologists recently.Fault gouge from Honghe and Qujiang active fault zones has been studied.It is,shown that microstructure,grain size,fabric and SEM micro-surface texture on quartz fragment in gouge were formed during steady-state slip stage,rapid shear motion associated with earthquakes and retro-metamorphism and other chemical process in active fault zone.As the result of this study,the author pointed that the south segmetn of Honghe fault zone may be steady-state slip active fault,and the north segment of Honghe fault zone and Qujiang fault zone are stick slip active fault.

It has been found from field observation and laboratory study that the fault rocks on the Beishicheng fault zone in Miyun region, Beijing can be classified into four main types: cataclasite series, mylonite series, pseudotachylite and fault gouge. They have distinct features in mineralogy, deformation and microfabric, representing the different mechanisms of their origin. It is shown by the features and occurrences of the fault rocks in this region that the fault zone had experinced two stage of movement of different mechanical behavior: the ductile shearing in the early stage and the brittle fracturing in the late stage accompanied by seismic events.The existences of pseudotachylite and cataclasite types of fault rocks can be regarded as the potential evidences for seismic events. The former is produced by preferred melting of minerals in country rocks due to the frictional heating on the fault plane during seismic faulting, while the later is a product of brittle fracturing due to rapid release of strain energy. During rapid frictional heating process of seismic faulting, the mafic minerals are the first to be melted, but the felsic minerals are melted at the temperature much higher than the mafic ones, so that the SiO2 contents in the pseudotachylite are much lower than that in the country rocks. That is why the crush breccia and breccia in pseudotachylite consist mainly of felsic materials, and this characteristics are completely different from that of magmatic origin.

Basing upon the petrological analysis under a microscope, the thermodynamic method and the data of anatexis, some mineral reaction formulae and their paragenesis assemblages are presented in this paper.