| The crustal stress pattern mentioned in this paper,including the characteristics of the crustal stress field and its mechanics,is an important research subject of earth science.China has a vast territory,and the crustal stress environment in different regions is significantly different.In order to understand the characteristics and causes of the crustal stress field in China,it is necessary to carry out crustal stress patten research across different scales,from the overall rule of plate scale,to the distribution of regional scales,and finally to the fine variations of local scale.Among them,the comprehensive analysis of multiple stress data is an effective way to study the general rule and regional difference of stress field,and the inversion from small earthquake data is the potential way to obtain the fine structure of stress field in key tectonic area.Based on the above ideas,the research work carried out in this paper and the main conclusions obtained are as follows:1.Based on the "Fundemental Database of Crustal Stress Environment in China",this paper collects and verifies different kinds of stress data in China and surrounding areas in recent years,and selects 6089 data records from it to participate in the compilation of World Stress Map 2016.The processed 5643 stress data has been compiled into World Stress Map 2016.In this paper,6344 reliable stress data in the range of 45°?155°E and 0°?60°N are selected from the combined database,which provides a more comprehensive and reliable data condition for the crustal stress field analysis in China.2.In this paper,the smoothing method for quantitative analysis of stress field law is improved,and 6344 reliable stress data are used to quantitatively calculate and analyze the general distribution law and different regional differences of crustal stress direction in China.The results show that the crustal stress model in China is generally distributed under the combined action of the Indian plate,the Pacific plate,the Philippine plate and the North American plate,and there is a plate-scale stress field characteristic,which is the stress directions rotate clockwisely around the Indian-Eurasian plate collision boundary.It indicates that the Indian-Eurasian plate collision is the main force source for controlling the plate-scale crustal stress model in China.In addition,the significant differences in mechanical factors at different scales,such as the complexity of plate boundary action,the complexity and strength of fault activity,and the severity of terrain changes,together create a crust stress patten with significant differences in stress field non-uniformities in different regions of China.The stress pattern is embodied as a staggered distribution formed by three broad and strong non-uniform strips,from west to east,followed by:Hindu Kush-Pamir area to Tianshan and Altai tectonic belts,along both sides of the North-South seismic belt,as well as the stripe extending from the Philippines and Taiwan to the Japanese island.These three stripes can be specified to 4 areas of strong non-uniformity:the Hindu Kush-Pamir area,the Tianshan area,the North-South seismic belt,and the Taiwan area.Among the three strong non-uniform stripes,the Northeast China and the hinterland of the Tibetan Plateau are two typical areas of uniform stress field.The strong non-uniformity distribution area of the North-South Seismic Belt extends widely,which further indicates that it is the boundary zone of the boundary structure between the east and west China.3.Through the principle analysis and theoretical data calculation,this paper points out that for the study of the fine structure of crustal stress field,the method of comprehensive focal mechanism solution from the P-wave polarities of small earthquakes has a preliminary data condition,and consequently is a potential but raw method.Then,through theoretical data experiments,synthetic data experiments,and actual stress field inversion detection,the degree of influence of traditional seismic location and velocity structure uncertainty on P-wave ray and its stress field inversion results is analyzed.The results show that the traditional seismic positioning error and the uncertainty of the P-wave velocity structure will bring significant errors(mean error?20°)to the take-off-angle of the P-wave initial polarity data with small epicenter distance(<200 km),and for P-wave initial polarity data near the epicenter distance of 100 km,the deviation from the source angle is more likely to be higher than 40°;in areas where the P-wave velocity structure is laterally non-uniform,it also leads to the change on the azimuthal angle to a certain extent,which may reach 10°orr above.At the same time,the seismic positioning error and the uncertainty of the P-wave velocity structure are also worthy of attention on the influence of the P-wave polarity inversion stress field,especially in the case when the amount of data is not very sufficient.It is quite necessary to more accurately constrain the seismic location and the three-dimensional P-wave velocity structure,which can effectively improve the accuracy and reliability of the tectonic stress field result from P-wave polarity inversion.In some cases,this improvement can reach more than 30%.4.Using the P-wave initial polarity data of the small earthquake in the middle section of the North-South seismic belt,which has been corrected by waveform cross-correlation and double-difference tomography,we adopt the method of composite focal mechanism to solve the fine crustal stress structure in the area,and analyze the stress field changes before and after the Lushan earthquake.The results show that the crustal stress structure in the middle section of the North-South seismic belt has significant differences in different tectonic positions,and also significant changes before and after the Lushan earthquake.The junction position of Longmenshan,Xianshuihe and Anninghe is the most complicated singular zone in the region,and the stress structure here changes significantly both on the lateral and vertical directions.There is a significant cross-fault change in the stress structure in the southern section of the Longmenshan fault.The front zone of the over thrust nappe is characterized by strong thrust-faulting extrusion,while the root zone is is characterized by strike-slip and even normal-faulting properties.These differences are the product of the long-term effects of the regional tectonic setting,and are related to deep structure,topography,as well as fault properties.In addition,in these two regions,there are obvious stress field changes before and after the Lushan earthquake,which are closely related to the activity of the Lushan earthquake and subsequent aftershocks.The studies in this thesis could be seen as the improvement based on the"Modern tectonic stress field map of China and its adjacent areas",both from the sides of quantification and the local-refinement. |
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