Contemporary Crust Deformation Of Chineese Mainland Determined From Earthquake Moment Tensors And GPS Observations

Chinese mainland is located in a complex deformation zone arising from collision between India and Eurasia plates, and there are lots of earthquakes occurred on it. So, it is very meaningful for us to analyze its seismic hazard and secular seismicity rate. Nowadays, many achievements, determined from earthquake moment tensors, quaternary fault rates or geodesy observations, have been made to research continental deformation in china and its adjacent areas, which provide basic magazines for analysis of seismic hazard and secular seismicity rate. Based on these achievements and irrationality in using earthquake moment tensors, we collect historic earthquake data of Chinese mainland and its vicinity between1900and2013, and surface ruptures and displacements of70earthquakes with magnitude greater than7.0. Then, we divide47of these large earthquakes into small segmentations with displacements and ruptures gathered before. Finally, we inverse strain rates and velocity models with earthquake moment tensors, quaternary fault rates and geodesy observations, and evaluate strain rate deficit, moment deficit and seismicity rate of Chinese mainland, meanwhile, we analyze seismic hazard by combining moment deficit and previous achievements.Following is the main works of this article,1. Determining strain rate and velocity models of Chinese mainland from earthquake moment tensors, quaternary slip rates and GPS observations with bicubic spline interpolation method. Then, evaluating dilatational rates, shear strain rates, principal strain rates and tectonic moment rates.2. Collecting earthquake moment tensors, surface ruptures and displacements of earthquakes with magnitude greater than7.0of Chinese mainland and its vicinity between1900and2013, and dividing47of these large earthquakes with length of ruptures greater than50km into small segmentations. Then, inversing strain rate and velocity models of study areas with earthquake moment tensors.3. Calculating strain rate and moment deficit based on strain rate model and historic earthquake data, and eliminating the aseismic deformation. Combining with the results of previous study, we analyze the seismic hazard of Chinese mainland.4. Using strain rate model and tapered Gutenberg-Richter distribution function, we evaluate seismicity rate of Chinese mainland and its vicinity. The results show that,1. The results show that the Tibetan plateau moves toward NNE direction and its velocity decreases gradually from south to north. The predicted velocity of Tibetan plateau indicates the crust shortening and eastward escape of highly plastic upper crust material, especially in the southern parts of plateau where goes clockwise around EHS (Eastern Himalayan Sytaxis). The velocity of western Himalayan thrust fault is about16mm a-1, the middle part is23mm a-1and the eastern is24mm a-1. The predicted velocity for the Altyn Tagh fault system is6-9mm a-1, which turns out that this fault zone is less active. The velocity for Tian shan areas is10-14mm a-1, and the western part is more active than the eastern, which shows that the Tarim basin goes clockwise relative to the Eurasia plate with a rotation rate of1°Ma-1and the axis located in eastern Tianshan. Contraction between northern India and Tian shan amounts to40-48mm a-1, of which a half is absorbed by the Himalaya thrust fault zone, a quarter across Tian shan and less than one fifth across the Altyn Tagh system.2. The characteristics of motion in Chuan-dian areas are that crust activity increases from south to north and from east to west, and goes clockwise. The fitted velocity is about8mm a-1in North china. The south china block moves toward SEE direction with a velocity of9mm a-1around a pole at (66°N,132°E,0.14°/a). The northeast china moves toward S84°E with a velocity of3.8mm a-1around a pole at (58°N,132°E,0.09°/a), which results in the extension of the Bakal region. The predicted velocity of VLBI station in Shanghai is7.4mm a-1that is comparable with the observation of8-11mm a-1.3. Earthquakes account for30-50percent of the expected motion of India relative to Eurasia and there is20mm a-1of slip deficit which is mainly composed of aseismic deformation such as fault creep and fold, insufficient of earthquake data and strain energy for potential earthquakes.4. During these113years, large moment deficit areas of Chinese mainland contain the Himalayan thrust fault zone, the Tian shan mountains, the Altyn Tagh fault system, the middle and south Tibetan plateau, the Chuan-dian areas, the periphery of the Ordos block, and the southeastern china. With the previous acquirements, there may be some potential strong shocks in these areas. There is little moment deficit in the Tarim basin, the south China and the northeastern china.5. There are48earthquakes with magnitude greater than7.0and1240earthquakes with magnitude greater than5.5in Chinese mainland during a century calculated by using strain rate model and tapered Gutenberg-Richter distribution function. Earthquake-prone areas in china are mainly the Himalayan thrust fault zone, the Tian Shan mountain, the Altyn Tagh fault zone, the east Kunlun fault zone, the Qilianshan-Haiyuan fault zone, the Xianshuihe-Anninghe-Xiaojiang fault zone, the Red River fault, the Sagaing fault and the periphery of the Ordos block.