【作者】 王勤彩；

【导师】 陈章立；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理， 2007， 博士

【摘要】 地震层析成像是研究地球非均匀结构的一种非常有效的方法。在研究长波长非均匀结构方面，速度成像得到了广泛的研究和应用。而在研究小尺度非均匀结构方面，尾波具有独特的优越性。本论文在介绍散射系数层析成像前，首先介绍了尾波归一化方法的基本原理，并把此方法应用到云南地区P、S波的衰减研究上，结果显示，由尾波归一化方法得到的P、S波衰减值与其它方法得到的结果基本一致，说明了尾波归一化方法在云南地区衰减研究中的有效性。然后利用多次散射模型、多流逝时间窗方法进行散射系数与吸收系数的分离，得到了大姚强震区及邻近地区的散射系数与吸收系数，为大姚强震群散射系数空间分布的研究准备了初值。本论文以单次散射模型、球形辐射源、一维线性速度模型为基础计算理论包络线，通过尾波归一化方法把理论与观测包络线结合起来形成非线性方程组，用迭代最小二乘法反演研究区的散射系数空间分布。大姚强震区的研究范围为60km×40km，研究区内网格水平间隔和深度间隔均设置为5km，外围区域网格间隔为10km，研究区及外围区域的网格点总数为1680，块体总数为1224。研究结果显示，M_s6.2、M_s6.1级地震序列的余震大多发生在高散射系数区内，主震发生在高散射系数区的边缘。震源深度较浅的M_s6.1级地震序列向北西、南东方向的扩展终止于两端的低散射系数区，M_s6.2级地震序列震源深度在研究区中部向下弯曲绕过低散射系数区，在深度剖面上呈弧形分布。大姚强震区10km深度上的高散射系数条带沿震源断层分布，暗示了震区下方断层破碎带的存在。大姚地震震源断层可能是通海一牟定断裂向北西方向的延伸。选取伽师强震群区的研究范围为72km×60km，研究区及外围区域的网格点总数为2725，研究区内网格水平间隔6km，深度间隔5km，外围区域网格水平间隔12km，深度间隔10km。伽师强震群区的散射系数分布图像显示，伽师强震群区下方中上地壳中存在明显的非均匀结构。在研究区的中部10-25km深度上有一低散射系数区，这个低散射系数区与速度结构中的P波高速异常区有很好的空间相关性。1997年的7次M_s≥6.0级地震发生在研究区中部低散射系数区的边缘。更多还原

【Abstract】 Seismic tomography is an effective method of studying heterogeneousstructure of the earth. Velocity tomography has got extensive applicationin studying long-wavelength inhomogeneous structure, however, instudying short-wavelength inhomogeneous structure, coda waves have theparticular advantage. In this thesis, Before introducing scatteringcoefficient tomography, we first introduced the basic theory of codanormalization and estimated attenuations of P and S waves in Yunnan region.The results show that our attenuation values are very close to thoseobtained by using other methods, Proving that coda normalization methodis effective in attenuation research of Yunnan region. And then, weestimated the scattering coefficient and intrinsic absorptionattenuation in Dayao strong earthquake area and nearby area by usingmultiple scattering theory and multiple lapse time window analysis method.Consequently, we prepared initial values for the research of spatialdistribution of scattering coefficient.Synthetic envelopes are calculated on the basis of the singlescattering theory, assuming spherical radiation sources and aone-dimensional depth-dependent velocity structure. An observationequation, which connects synthetic and observed energy densities, isobtained employing coda normalization method. Finally, we obtain thespatial distribution of scattering coefficient of research areas usinga standard ]east squares technique iteratively. The research region ofDayao strong earthquake area is 60km×40km. We set 1680 Grid points with5km spacing in the central part of research area and 10km spacing in thesurrounding area and there are total 1224 blocks. Obtained results showthat most aftershocks of M_S6.2 and M_S6.1 earthquake sequences occuredwithin large scattering coefficient zones and two main earthquakesoccured on the edge of large scattering coefficient zone. The extension of M_S6.1 earthquake sequence towards northwest and southeast ends at lowscattering coefficient zones. The aftershock focal depth of M_S6.1earthquake is relative shallow. M_S6.2 earthquake sequence bends downwardsto round a low scattering coefficient zone and forms an arc shape insection. The large scattering coefficient zone at depth of 10km isdistributed along the main shock faults, which implies that there arefault-damaged zones under Dayao strong earthquake area. The main shockfaults are supposed to be the extension of Tonghai-Mouding fault. Theresearch region of Jiashi strong earthquake swarm area is 72km×60km. Weset 2725 Grid points with 6km (horizontal) and 5km(vertical) spacing inthe central part of research area and 12km and 10km respectively in thesurrounding area, thus there are total 2106 blocks. The results show thatthere is obvious inhomogeneous structure in middle and upper crust, A lowscattering coefficient zone exists at depth of 10-25kmin the central partof research area and forms a good spatial correlation with high P-wavevelocity zone. Seven M≥6.0 earthquakes in 1997 occurred at the centeror edge of the low scattering coefficient zone.更多还原