Large amounts of seismic records from Zhejiang digital seismic network are collected,and by double difference seismic tomography,fine velocity structure and local heterogeneity of upper crust in Zhejiang Province and its surrounding areas are studied,and the relationship of the crustal velocity structure to the local active faults,geological and geographical structure is discussed. Research shows that there is a large-area low velocity zone developed in northern Zhejiang at depths between 3.5km and 6.5km,and also some low velocity zones distributed sporadically in southern Zhejiang,mostly around Shanxi Reservoir in Wenzhou. The research indicates that most earthquakes happened along active faults or active fault segments,and are concentrated in zones. These zones are almost all in the transitions between low to high velocity zones,and are significantly related to the regional topographic features. The correlation relation derived by this paper between earthquake,active fault,and geological and geographical structure will be of theoretical value and practical significance to the study of seismogenesis and the prediction of future strong earthquakes.

Statistic analysis has been made on the characteristics of the contemporary tectonic stress field of East China based on 143 sets of single focal mechanical solutions of moderate and small earthquakes and on 17 sets of composite focal mechanism solutions. Results show that the stress field of East China exhibits a NNE (about 80?) oriented principal compression and NNW (about 350?) principal tension, and the principal stresses are mainly horizontal or near-horizontal. In the context of basically consistent orientation and action mode of stress field, there are some variations in the stress field among different seismotectonic regions, which are possibly related to the distribution of major active faults in the respective regions. This indicates that fault slip may be dominated or affected by existing tectonics. The feature of earthquake fracture and the orientation of fault slip of contemporary earthquakes in East China have been analyzed with data of focal mechanism solutions of contemporary moderate and small events, and of the orientations of major axis for innermost isoseismal of historical and contemporary events and so on. It indicates that the earthquake fractures of East China extend at large in NE and NW directions, and sometimes with NNE, NEE, NWW, or near EW directions. The movements of earthquake faults are mainly of strike-slip or near strike-slip with oblique-slip component. There exist some regional variations in the movement of earthquake faults. The historical moderate and strong events in East China exhibit mainly a NE trending slip, while the modern events show the NW-SE trending slip on the land and NE and NW trend slip in the sea area.

This paper discusses ultrasonic mechanism of the sealed-H₂ release from basalt rock on the basis of experiments.A small amount of released H₂ by ultrasonic vibration is escaping H₂,whereas most H₂ is absorbed H₂.Both phenomena can be regarded as a precursory H₂.So,it is possible to use H₂.to.forcast earthquake.Seeing that the intensity of u.v.and the its duration were constant in the experiments and the amount of released H₂ gas increased during each vibration,abnormal H₂ seems not to be representative of accoustic emission intensity,thus suggesting that the intensity of the failure of rock may be representative of the earthquake magnitude.