Many of the large earthquakes in the continental crust nucleate at the bottom of the seismogenic zone in depths between 10 and 20km which is related to the broad so-called ‘brittle-to-plastic or brittle-to-ductile’ transition region. From the field studies and seismic data, we could know that the dominant deformation mechanism at the base of seismogenic zone is likely to be semi-brittle flow of fault rocks. The physical and chemical processes acting in the ‘brittle-to-plastic’ transition are of great interest for a better understanding of fault rheology, tectonic deformation of the continental lithosphere and the generation of strong earthquakes. So it’s of great significance to know more about this transition. Despite the importance of semi-brittle flow, only few experimental studies are relevant to semi-brittle flow in natural rocks. In order to study the semi-brittle deformation and rheological characteristics of granite, we performed a series of transient creep experiments on fine-grained granite collected from the representative rock of Pengguan Complex in Wenchuan earthquake fault area using a solid-medium triaxial deformation apparatus(a modified Griggs rig). The conditions of the experiments are under the temperatures of 190~490℃and the confining pressures of 250~750MPa with a strain rate of 5×10^-4s^-1. The temperature and pressure simulate the in-situ conditions of the Wenchuan earthquake fault zone at the corresponding depths of 10~30km. We observe the microstructures of the experimentally deformed samples under the scanning electron microscope(SEM). The mechanical data, microstructures and deformation mechanism analysis demonstrate that deformation of the samples with experimental conditions could be covered by three regimes: 1)Brittle fracture to semi-brittle flow regime. We could see the strain and stress curves of the samples characterizing with strain hardening behavior and without definite yield point under low temperatures and pressures, which correspond to the depths of 10~15km; 2)Brittle-ductile transition regime. The strain and stress curves of the samples tend to be in a steady state with definite yield point under temperature and pressure at the depths of 15~20km. The main deformation mechanism is cataclasis, and dynamic recrystallization and dislocation creep are activated; and 3)Ductile flow regime which is at depths of 20~30km. The strength of granite increases with depth and reaches to the ultimate at the depth of 15~20km, and then decreases with depth at 20~30km. Based on the analysis of strength of granite, microstructures and deformation mechanism, we conclude that the granitic samples deformed with the characteristics of transient creep, and the strength of Longmenshan fault zone reaches maximum at the depths of 15~20km where it is in the brittle-to-plastic regime. Based on the Mohr circle analysis, the rupture limit at depths of 15~20km is close to the limit of friction, and at the same time, this depth range is also consistent with the focal depth of Wenchuan earthquake. Therefore, it implicates that the deformation and strength of Pengguan complex granitic rocks should control the nucleation and generation of the Wenchuan earthquake.

By the analysis of deformation in outcrop area and fissure measurement of core rocks in Zhangqiang depression and its adjacent area, we divide the geological history of this region into eight tectonic stress phases and determine the tectonic stress states and deformation forms of each phase. We conclude that the tectonic stress fields of the late Jurassic and the Cretaceous resulted in the formation and development of faulted basins, and the stress state of the late Jurassic was nearly E-W extension. Between the end of Fuxin Group and the beginning of Quantou Group sedimentation stages, the stress fields resulted in the close of basin faulting stage and deformation of the late Jurassic caused by the change of stress states from E-W extension to E-W compression. In the Cretaceous phase, the principal stress direction was E-W compression which caused the regional depression as a whole in the early period and uplifting and erosion widely in the later time. The principal stress direction was NW-SE compression in the Eogene, and was NEE-SWW compression since the Neogene. Two phases of stress fields in Cenozoic only caused some reactive faults, the deformational strength was less than that in Jurassic and the Cretaceous.

In the study of seismotectonics,much attention is usually paid to active fault zones which have long evolution history and large scales.However there are also newly-generated seismotectonic zones in the recent tectonic stage.Seismicity has a close relation with both kinds of tectonic zones.It can be seen that Tangshan-Hejlan-Cixian seismic zone is a new crustal shear fracture zone which has been developed since the Neogene as well as a newly-generated seismotectonic zone in North China based on analysis of the data of earthquakes and geological structures.

Soil-forming factors are involved in original rocks, climate, living things, topography and time. If we wish to ascertain accurately the soil-forming time, all remaining factors must be be kept constant. The physical parameters of any soil are related to time. The authors have established a regression equation and correlation coefficients between characteristic parameters and formation time of soil layer B_ms on the alluvial fan in Heyuan area, Guangdong. The age of third-step alluvial fan has been determined by using growth rate of secondary minerals. A chronosequence cf the soil development of the alluvial fan has been set up in Heyuan area, Guangdong.

Jianghan-Dongting Lake basin is a large-scale Meso-Cenozoic basin in South China. Its geological structure, deep-seated structure, tectonic evolution, neotectonic activity and seismicity are analysed basing on the data of geology, geophysis and earthquakes in the basin region.The basin consists of Jianghan and Dongting Lake depressions and Huarong uplift. WNW-EW-trending secondary segs and positive land forms controlled by the faults developed in Jianghan depression, but NEN-NE striking secondary positive forms and segs controlled by the faults developed in Dongting Lake depression. The basin has undergone a complex process o'f tectonic evolution. There is intensive neotectonic activity in the basin region. Mid-intensity earthquakes are closely related to the structures with differential activities in Quaternary.

In this paper, characteristics of neogenic clay minerals and micro-surface texture of quartz fragment in fault gouge are discussed. Clay minerals are analysed mainly by X-ray diffraction, whereas miero-surface texture of quartz fragments is studied by SEM. The relative age of faulting is determined with the analysis of corroded surface texture of quartz fragments.