【作者】 王兆国；

【导师】 刘财； 冯晅；

【作者基本信息】 吉林大学 ， 固体地球物理学， 2010， 博士

【摘要】 东北地区濒临欧亚板块与太平洋板块碰撞带,并且东北地区的构造复杂,在此两者的影响下,东北地区地震研究有着重要意义。为此,我们利用2001年—2008年的走时数据和2007年11月—2009年3月我们布设的台站的走时数据以及波形数据,对东北地区的地震进行定位、层析成像和震源机制解的研究。研究结果表明:东北地区发生的地震大体可以划分为四个地震区,但主要分布在断裂分布带上,大多发生在盆地外围隆起区,而在断陷盆地内部很少发生。南边地震深度较深,而北边地震深度较浅。44。N南北两侧差异明显,各存在两个地震活跃层位。华北板块是由SE向倾向于NW向的“低-高-低-高”的四层速度异常带构造成的“穹隆”式的结构;华北板块北缘增生带,主要体现为三层“低-高-低”条带状速度异常结构;额尔古纳-兴安地块表现为由SW倾向于NE方向的三层“低-高-低”条带状速度异常结构;松嫩地块SW部,即经过松辽盆地的区域,表现为“高-低-高”的三层条带状速度异常结果,NE部过渡为“低-高-低-高”的近似水平的四层条带状速度异常,最上层的低速带较薄;兴凯地块与佳木斯地块表现为“低-高-低”的三层条带状速度异常,与松嫩地块的NE部地层连续性较好,但兴凯地块与佳木斯地块相同性质的速度异常,深度较浅。长白山火山下方存在着低速异常体,与他人的研究工作,长白山火山是一个弧后板内火山是相一致的。震源的位置主要分布在高速异常区与零速度扰动线附近,也即高速异常与低速异常相交的区域,可见震源的发生与高速异常有很密切的关系,应发生在高速异常区或速度变化过渡带上。华北板块有个别地震分布于低速异常区内,这些地震与地层中水的作用有关。深源地震的震源机制解为典型的板块俯冲造成的结果,远离东北地区的日本海域的深源地震主节理面近乎于水平,辅节理面近乎于垂直,因此俯冲角度较小,到东北的珲春地区,俯冲角度增大。陆地浅源地震,从震源机制解来看,一对节理面近乎于垂直,主要为右旋走滑及左旋走滑断层,为地块走滑造成。更多还原

【Abstract】 The earthquakes which are the Violent release pattern of energy in the Earth, give a huge disaster and economic losses to the persons. The Wenchuan earthquake occurred on May 12, 2008, the Haiti earthquake occurred on Jan. 12, 2010 and the Chile earthquake occurred on Feb. 17, 2010 all give tremendous losses and casualties. it has long been a goal of seismologists to really understand the mechanism of the earthquake. There is the chinese largest oil field-Daqing Oilfield in the Northeast china, and there are a large number of industrial and character-intensive areas here,but the Northeast China is located in the Eurasian Plate and the Pacific plate collision zone, near one of the world’s two major seismic zone, Central Pacific seismic zone, seismic activity has its particularity. To further study the causes of earthquakes as well as the relationship between crustal structure, the Northeast China is chosen to be the study area.We selected seismological travel time data from 2001 to 2008 in the Northeast seismological stations net and seismological travel time and waveform data from 2007 to 2009, in the 16 stations we laid in the Northeast China. We did the re-positioning, tomography and focal mechanisms to the earthquakes in the Northeast China.to try to explain the cause of the earthquakes and its relationship with the crust-mantle structure and stress field in the Northeast China.For the inversion of geophysical work, the well posed solution is very important, including wellposedness existence, uniqueness and stability. For the inversion problem, the establishment of an appropriate model is very important. The earthquake relocation, tomography and the inversion of focal mechanisms, are based on one-dimensional velocity model. So we first determine the one-dimensional velocity model. The one-dimensional Global velocity model has four kinds. We go through the average standard deviation of the residuals of the theoretical and actual travel time to determine the one-dimensional velocity model. When the average standard deviation is smaller, it illustrate the difference between the theoretical travel time and the actual travel time is smaller and the model is more similar to the actual formation.After the establishment of one-dimensional velocity model, we take the travel time data in the Northeast China to relocate the earthquakes source to analyze the northeast China’s spatial distribution of earthquakes, the depth layer of the earthquake based on the re-positioning results,Using the travel time data, we carry on the tomographic imaging of the crust and mantle in the Northeast China using the pseudo-bending ray tracing to study the crust and mantle in Northeast China , the earthquake distribution and its relationship with the crust-mantle structure and the structural characteristics of the Changbai volcano in Northeast China.We carry on the inversion of focal mechanisms with moment tensor inversion in Northeast China to determine the principal stress axis, advocated force axis. The very important issue in moment tensor inversion is the synthetic theory of wave. The Green’s function in the waveform synthesis problem is calculated to use the coefficient matrix and the wave number integral method, then according to the synthetic theory waveform fit with the observed waveform , the best focal mechanism is found.According to the relocation research, the earthquakes in the Northeast China can be roughly divided into four area, which are mainly distributed in the fracture areas, mostly in uplifts surrounding the basin area, rarely in the sedimentary basin; In the spatial distribution, the depth of the earthquakes in southern area is deeper and the depth of the earthquakes in northern area is shallower. There are significantly differences between the north and south sides separated by the latitude 44°, which separately has two active earthquake layers.Based on the tomographic result, the horizontal sections can be divided into 3 bands of speed anomaly with nearly NE-SW direction. A band anomalies shows low anomaly in the Northeast, high-speed anomalies in the central, the major changes in the southwest is that the high-speed anomaly changes into the low-speed anomaly from 2km section to 5km section , which changes into high-speed anomaly untile 30km section; B band anomaly always shows low-speed anomaly in the southwest, whose area increases continuously, and it shows low-speed anomaly in the Northeast and quickly disappears and change into high-speed anomaly, take on the low-speed anomaly in the 30km section, and in the central of the section it shows high-speed anomaly and only performance low speed abnormal in the 30km section. C band anomaly performance the low-speed anomalies in the northeast and high-speed anomalies in southwest, and both areas are expanding. From the NE and NW vertical profile sections, the North China plate is composed of "low - high - low - high" four velocity anomalies which is inclining to NW to form a "dome" structure; The northern accretion zone of North China Plate takes on“low-high-low”three velocity anomalies; The Ergun-Xingan masiff presents“low-high-low”three velocity anomalies which is inclining to NE; The SW part of the Songnen masiff which crosses the Songliao basin shows“high-low-high”three velocity anomalies, and the NE part of the Songnen masiff takes on the nearly horizontal“low-high-low-high”four velocity anomalies, and the top layer is thin; The Xingkai masiff and the Jiamusi masiff both show“low-high-low”three velocity anomalies, and compared with the Songnen masiff the stratum has good continuity, but the same characteristic anomaly in the Xingkai masiff and the Jiamusi masiff is shallower than in the Songnen masiff..The Changbai volcano has low velocity body below, ,which is consistent with previous research work which is a volcanic arc plate. The locations of the earthquakes source are mainly in the high anomaly areas or near 0 velocity disturbance line, ie, high-speed anomaly and low-speed anomaly intersection region, which shows that the earthquake occurrence has close relationship with the high-speed anomaly. The earthquakes should occur in the high-speed area or anomalies transition zones. The individual earthquakes in North China plate are in the low velocity zone, which has close relation with the water.The focal mechanism can be divied into two types based on the focal mechanism solutions. Deep earthquake focal mechanism solutions is the typical result of plate subduction, the main plane in the Japan Sea is nearly horizontal and the secondary plane is nearly vertical, so the dive angle is small,and near the northeast, the subduction angle increases; A pair of plane of focal mechanism solutions of the shallow earthquakes in the land is nearly vertical ,which indicate the dextral strike-slip and sinistral strike-slip fault caused with the massif slip movement.Through the focal relocation, tomography and focal mechanism studies, we can see that the Northeast region is influenced by the subduction of the Pacific plate whose subduction angle increases from SE to NW and velocity structural abnormalities among the masiff, make the blocks strike-slip movement to form four major earthquake zone in the deep fault belt.更多还原