西太平洋俯冲板块中、深源地震高精度定位及应用研究

发布时间：2018-08-12 18:44

【摘要】：由于太平洋板块向西北方向的俯冲,造成了日本东北岛弧一带下方俯冲板块内存在丰富的中、深源地震。甚至造成了中国东北地区下方存在深源地震。本研究利用日本台网及中国东北地区台网收集到的中、深源地震数据进行重定位,并结合震源机制解,探讨板块的结构形态和应力状态,进而解释中、深源地震的发震机制。本研究采用改进的双差定位作为地震重定位方法:理论走时计算采用三维射线追踪;计算偏导数系数时选用球坐标系,提高深部地震定位的精度。在对实测数据定位前,本研究进行了理论测试,验证了改进双差定位方法的有效性及定位精度特点。并且在测试阶段,确定了定位参数的选取原则。为了简化操作,本研究在定位源程序的基础上利用Matlab软件编制了可视化界面。通过对日本东北地区中源地震的重定位发现,该地区下方沿俯冲板块上、下边界存在两条平行的地震带,两条地震带在深部逐渐融合。根据上、下两层内地震的震源机制解,发现上层地震带内的应力为挤压力;而下层地震带内的应力为拉张力。本研究推断造成该现象的原因是板块俯冲至地幔过渡带后速度逐渐减小,由于自身重力作用发生向下弯曲作用。通过对中国东北地区深发地震的重定位发现,同时利用中国和日本台网记录的数据进行重定位比单独用中国或日本的数据进行定位得到的精度高。重定位后的深源地震基本位于与板块上边界相距30km的条带内。结合震源区低速异常结构和震源机制解,认为深源地震的发生与地幔过渡带中板块内部存在亚稳态橄榄岩存在联系。在浮力和重力的共同作用下,亚稳态橄榄岩处于挤压应力状态,这可能是造成深发震源带的原因。
[Abstract]:Due to the subduction of the Pacific plate to the northwest, there are abundant moderate and deep earthquakes in the subduction plate along the northeastern island arc of Japan. It even caused a deep earthquake in northeast China. In this study, the data collected from Japan and Northeast China are used to locate the moderate and deep source earthquakes, and combined with the focal mechanism solution, the structural shape and stress state of the plate are discussed, and the seismogenic mechanism of the medium and deep source earthquakes is explained. In this study, the improved double difference location is adopted as the method of seismic resetting: the theoretical travel time is calculated by 3D ray tracing, and the spherical coordinate system is used to calculate the partial derivative coefficient to improve the accuracy of deep seismic location. Before locating the measured data, a theoretical test is carried out to verify the effectiveness and accuracy of the improved dual-difference positioning method. And in the test stage, the selection principle of location parameters is determined. In order to simplify the operation, the visual interface is compiled by using Matlab software on the basis of locating source program. It is found that there are two parallel seismic zones along the subduction plate under the middle source earthquake in northeastern Japan, and the two seismic belts merge gradually in the deep part of the area. According to the focal mechanism of the upper and lower layers of the earthquake, it is found that the stress in the upper seismic belt is extrusion force, while the stress in the lower layer is tensile tension. The reason for this phenomenon is that the velocity of plate subduction to the mantle transition zone gradually decreases and the downward bending occurs due to its own gravity. By relocating deep earthquakes in northeast China, it is found that the accuracy of relocating by using the data recorded by China and Japan network is higher than that by using data from China or Japan alone. After relocating, the deep focus earthquakes are located in the 30km zone separated from the upper boundary of the plate. Combined with the low velocity anomalous structure and focal mechanism solution in the focal area, it is concluded that the occurrence of deep source earthquakes is related to the existence of metastable peridotite in the plate in the mantle transitional zone. Under the combined action of buoyancy and gravity, the metastable peridotite is in the state of compressive stress, which may be the cause of the deep earthquake source zone.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.3

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