青藏高原东南缘地区三维精细结构与地震活动性研究

Both seismicity and velocity structure in the custal and upper mantle can give us important information to the lithespheric flow and deep driving mechanism in sourtheastern Tibet.However,there are uncertainties in estimating focal depths and in boundary of low-velocity ,the key point to the lithespheric flow and deep driving mechanism is less clear. In this proposal, we plan to take advantage of both the absolute and differential arrival times (including both the waveform cross-correlation and catalog time difference data) recorded by national and regional seismic networks and the temorary seismic stations after Wenchuan earthquake. We will apply the double-difference tomography method to determine a detailed high-resolution 3D crustal and upper mantle velocity structures as well as the absolute and relative hypocenter parameters under the southeastern Tibet region. Compared with standard tomography, the use of differential arrival times removes most of imprecise picks and correlated errors , which will in turn remove some fuzziness from the velocity model. By reducing systematic errors using the more accurate relative arrival times to improve relative and/or absolute location accuracy, double difference tomography will produce an improved velocity model beneath the southeastern Tibet region.Simultaneously, it will yield event locations of a quality equivalent to those of the double difference location method. Consequently, the double difference tomography is efficient in relocating large numbers of earthquakes accurately as well as characterizing the velocity structure finely. Our project should give more accurate view of seismicity and a more reliable velocity structure beneath the southeastern Tibet region than previous studies. The seismic results will be used to answer the fundamental question, ie., where is the boundary of low velocity in the middle and lower crustal beneath the southeastern Tibet, what is the relationship between the seismicity of small earthquakes and velocity structures near the active faults in the southeastern Tibet region. Our tomographic results will deepen our understanding of the lithespheric flow and the dynamic source of stron earthquakes.

青藏高原东南缘地区高精度的三维精细速度研究可以为青藏高原的物质运移与深部驱动机制提供现象和证据，确认地壳中低速层的边界至关重要。探寻地震与速度异常体以及活动构造之间的关系对于深入认识青藏高原现代构造活动状态、地震孕育的深部构造背景、地震的破裂过程有着十分重要的作用。 本项目计划采用中国地震台网、区域地震台网和汶川震后流动台网记录的人工爆破资料、天然地震体波观测报告和高精度波形数据，改进初始模型和网格节点的划分、提高地震定位精度、联合使用多种类型地震波的绝对到时数据和相对到时数据、用双差地震层析成像方法联合反演青藏高原东南缘地区高分辨率的三维速度结构和精确的震源参数，确定地壳中低速体的边界和横向变化，获得该区域内主要活动断裂与地震活动性之间的联系，加深对青藏高原东南缘地区的物质运移和深部驱动机制的理解，为该区域的强震孕育机制和地点提供重要信息。

青藏高原东南缘地区高精度的三维精细速度构造研究可以为青藏高原的物质运移与深部驱动机制提供现象和证据，确认地壳中低速层的边界至关重要。本研究中采用中国地震台网、区域地震台网和汶川震后应急台网记录的人工爆破资料、天然地震体波观测报告和高精度波形数据，改进了初始模型和网格节点的划分、提高了地震定位精度。联合使用地震波绝对到时数据和高精度的相对到时数据、用双差地震层析成像方法给出了青藏高原东南缘地区重点区域：龙门山断裂带、芦山震源区和昭通地区的高精度的三维速度结构及震源参数，并对该地区地震的震源深度分布与活动构造之间的关系做了非常深入细致的研究，探讨了青藏高原东南缘构造运动的深部驱动机制及其对强震的控制作用，为研究未来强震可能发生的地带和地域提供重要信息。