Rticle Source Refraction/Reflection Seismic Tomography And Application In North China

We reviewed the geology and geophysical research in North China and Yinchuan Basin where we concerned in this dissertation, and discussed the importance of Urban active fault exploration in these regions.In chapter2, We reviewed the travel time tomography techniques and introduced advance of seismic tomography. Travel time tomography was consisted of four major techniques:1) model parametrization,2) forward calculating,3) inversion calculating, and4) model assessment. We provided a classic tomography example to explain the importance of the major techniques and what the travel time tomography could not to do.In Chapter3, We discussed the modeling and tomography strategies in seismic refraction/wide-angle reflection data processing.In Chapter4, We utilized modeling software Rayinvr and travel time tomography techniques to processed the refraction/wide-angle reflection data which was the densest recently in North China. The results of upper crust tomography indicated upper crust velocity structure of the North China Basin was strong lateral heterogeneity and major geology layers shared same geometry. The shallowest depth of sediments boundary was2km in Cangxian uplift, and the deepest depth was button to8km in Jizhong Depression. There was the plain region of Yanshan Uplift in northwest of240km of the profile, the sediments boundary was very shallow, generally was2km or shallower than2km, especially in Tongxian Horseback. There was the north China basin in southeast of240km of the profile, the sediment boundary was deeper, from3km to8km. There were three sag basins, Dacang Sag, Wuqing Sag, Huanghua Sag and one uplift Cangxian uplift. The deepest sediment was in Wuqing Sag and Huanghua Sag, button to8km. In Huanghua Sag, located the southeast of the profile, velocity contours was obviously dense from5.6km to5.8km, which mean the sediment boundary was low velocity5.6km/s, indicated Huanghua Sag depressed down and sediment was reconstructed in depressing motion.The results of3D and2.5D tomography indicated the differences between the basins in geology material. The major material of Sediments in Beijing Sag was velocity less than4.5km/s, but the material of velocity from3.5km to4.5km/s was not too different with other basins. That means Beijing Sag had much connections with Yanshan motion.The modeling results using Rayinvr indicated there were four crust boundaries in North China. The first boundary was the bottom of upper crust, which was strong lateral heterogeneity, velocity from5.80km/s to6.0km/s, and depth form1km to7km. The second boundary was the Conrad boundary which velocity was6.2km. The third boundary was the top of lower crust which velocity was65.km/s. The forth boundary was the Moho boundary which was the30km in southeast of profile located Tianjin Coast and down to40km in northwest of profile located in Yanshan mountain.In chapter5, We applied the first arrival travel time tomography to3D Seismic array data in Yinchuan Basin. Inherited non-uniqueness and nob-linear in tomography was more strong in3D problem than2D situation. Then, We using non-linear checkboard technique to assessment the final model and provided the qualify resolution according semblance among all the checkboards. The results indicated the Yinchuan Basin was consisted of two deep sediment basins bottom to7km. The sediment boundary in the west and the east was very shallow and in the basin was very deep. Luhuatai fault, Yinchuan-Pingluo fault and Huanghe fault exhibited NNE direction and constructed by obviously velocity difference. Luhuatai fault was dip to east and bottom to sediment. Yinchuan-Pingluo fault was dip to west and bottom to sediment. Huanghe fault was dip to west and bottom to sediment. The tomography results and checkboard testing revealed heterogeneous in horizon that was consistent with topography. The structure direction of Yinchuan basin was NNE, sediment boundary in the west more deeper than the east. There were two sediment centers in Yinchuan basin and two basins was demarcated from Suyukou to Yaofu. High velocity structures in the west and the east folded deep sediment revealed the graben feature of Yinchuan basin. The deepest sediment in Yinchuan basin located from Luhuatai to Xidatan, controled by Luhuatai fault, and the depth was8-10km. According to others research results, we interpreted our tomography result that the Cenozoic bottom velocity was5.65km/s. The west of Yinchuan basin was Helan mountain, the east was Lingyan tableland, and both sediments were shallower than4km.In chapter6, we analysis the complicated seismic phase WG and multiple P Phase and revealed the nature of these complicated phases. Synthetic seismogram technique was applied to modeling the1D crust structure which could predict the observed seismogram. The travel times of multiple phase was applied to modeling velocity structure using tomography technique.In chapter7, we introduced the advance of seismic tomography including conventional ray theory, Fennel volume tomography, Frequency denpendent travel time tomography and waveform inversion.