In order to quantitatively analyze the reliability of the composite fault plane solution of small earthquakes, the Bootstrap sampling technique is introduced into the grid search method, and the ideas and methods for calculating the confidence interval from the grid search method are proposed initially. There are two sample sets that can represent the characteristics of the composite fault plane solution. One sample set is the optional solutions obtained by the grid search method and the other is obtained by the Bootstrap sampling technique. Then, we calculate the confidence intervals of the two sample sets (P, B and T axis). The research results of tectonic stress field in southern Jiangxi Province are relatively few. In view of such situation, we use the focal mechanism solutions of small earthquakes to calculate and analyze the composite fault plane solution and the confidence interval. This study shows that the confidence interval of the principal stress axis can be obtained well by both of the sample methods. The reliability of the results and the confidence range of the principal stress axis can be better represented by the confidence intervals. The middle principal stress in southern Jiangxi Province is nearly vertical, and the maximum and minimum principal stresses are nearly horizontal. The direction of maximum principal stress is NWW-SEE and that of the minimum principal stress is NNE-SSW. And, the area is in a strike-slip stress regime. The results are consistent with previous studies, and the stress directions obtained by previous researchers are within the confidence interval calculated by this paper.

Based on Zoback's method for estimating the tectonic stress magnitude and the two assumptions, we consider the conditions that three principal stresses are vertical principal stresses respectively(corresponding to three kinds of tectonic stress types). We deduced the formulae for estimating the tectonic stress magnitude by using the stress form factor and frictional strength of the fault and discussed the correlative influence of friction coefficient, pore pressure parameter and stress form factor on the stress value. When the maximum principal stress is approximately horizontal (when stress regime is strike-slip or reverse), the maximum principal stress (or the slope of stress increasing linearly with depth) is positively related with the friction coefficient and negatively related with the pore pressure coefficient. When the minimum principal stress is approximately horizontal (when stress regime is strike-slip or normal), the minimum principal stress (or the slope with depth) is negatively related to the friction coefficient, and positive to the pore pressure. Besides, these three parameters have great influence on the estimation of the tectonic stress magnitude. If the friction coefficient is too big and the pore pressure is too small, there could be a wide difference between the slope of the maximum principal stress increasing with depth and the slope of the minimum principal stress increasing with depth, which could lead to an unreasonable result. Our method is just an approximate estimation for the tectonic stress magnitude when crustal rocks have undergone brittle rupture or frictional sliding. The estimated results are not the tectonic stress magnitude when crust is in steady state.

Based on the synchronized observation data of 1s sampling rate Network MT(N-MT)system with FHDZ-M15 geo-magnetometer installed at Jinghai seismic observatory in the "Tenth Five-Year Program" period,we carried out the MT measurement at a stationary station. Robust technology was employed in data processing to the data recorded at Jinghai observatory from January to June,2008. The tensor impedances were obtained. The temporal abnormal change of 18 apparent resistivity and impedance phases of same-period in the range of periods of 6～600s was analyzed. The results show there exist changes in some periods of apparent resistivity and impedance phases before the M_L 4.2 Lulong earthquake on March 17,2008. In this study,the period of data used corresponds to the depth of 5～ 50km,a range of focal depth of North China. The result indicates the change of electrical conductivity of the strata in the source area before and after the earthquake. The MT method can reflect the electrical conductivity changes at the source area more directly than the existing geoelectric observation methods,and it has bigger advantage for deeper exploration.

Yanhuai Basin contains Yanfan Basin and Huaizhuo Basin,which are connected one another.According to field seismo-geological investigation and fault slip observation,the active faults in northeast direction in Yanfan Basin are mainly dextral strike-slip,with some cases of normal fault.But in Huaizhuo Basin,the situation is opposite,the active faults in northeast direction are mainly normal faults,with some cases of strike slip.However,in the whole Yanhuai Basin,the active faults in northwest direction are mo

Owing to strong and permanent Cenozoic re-orogenic processing, a lot of EW-striking active thrusts and folds have been developed in Tian Shan, resulting in crustal shortening in NS direction. There also exist NW-striking transform-like strike-slip faults that cut the Tian Shan and accommodate uneven crustal shortening larger in the west and smaller in the east. The seismogenic structures in and around the Tian Shan mainly include EW-striking thrust ramps or blind thrusts and NW-striking transform-like strike-slip faults. The 2003 AD Bachu-Jiashi earthquake is located at south of the Kalpintag nappe. A NE-trending deep seismic reflection profile about 50km long across the epicenter has been conducted after the earthquake. From this reflection profile four blind faults are identified. Together with earthquake relocation, these identified blind faults are used in the paper to interpret the seismogenic structures of the 1997 AD Jiashi strong earthquake swarm and 2003 AD Bachu-Jiashi earthquake. The 1997 AD Jiashi strong earthquakes were generated mainly by a NW-striking buried transform-like strike-slip fault, while the 2003 AD Bachu-jiashi earthquake by blind thrusts in front of the Kalpintag nappe.

Based on analysis of distribution of 2 660 earthquake focal mechanism solutions from “Database of Crustal Stress of China and Adjacent Area” (updated to December, 2003), the regional characteristics of focal mechanism solutions are studied. In the Northeast and North China stress regions, the orientations of maximum horizontal stress mostly are in the near EW direction and NEE-SWW direction. The strike-slip focal mechanism is predominant in Northeast and North China stress regions. In the South China stress region, the predominant orientation of maximum horizontal stress is in NE-SW direction. The focal mechanisms mainly include thrust faulting and strike-slip faulting. In the Xinjiang stress region, the predominant orientation of maximum horizontal stress is in near N-S direction. There is a significant number of thrust faulting events and strike-slip faulting events in Xinjiang stress region. In the south Tibetan stress region, the predominant orientation of maximum horizontal stress is in near N-S direction, and the focal mechanism solutions are of strike-slip and normal faulting. In the stress region of north Tibet plateau and in the northeastern edge, the predominant orientation of maximum horizontal stress is not concentrated, and the focal mechanisms mostly are of strike-slip faulting, with some normal faulting and thrust faulting.