利用尾波包络线反演方法研究伽师强震群区地壳的非均匀结构

Imaging crustal heterogeneity in Jiashi strong earthquake swarm region by coda envelope inversion analysis

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,用迭代最小二乘方法反演伽师强震群区的散射系数空间分布.结果表明,伽师强震群区下方中上地壳中存在明显的非均匀结构.在10～25km各深度图像上,研究区中部都存在一低散射系数区,这个低散射系数区在10km、15km深度被高散射系数区包围,在20km深度仅其东侧存在高散射系数区.1997年的7次Ms≥6.0级地震发生在研究区中部的低散射系数区内或低散射系数区向高散射系数区过渡带的低散射系数一侧.

Synthetic envelopes are calculated on the basis of the single scattering theory,assuming spherical radiation sources and a one-dimensional depth-dependent velocity structure.An observation equation,which connects synthetic and observed energy densities,is obtained employing coda normalization method.Finally,we obtain the spatial distribution of scattering coefficient of Jiashi strong earthquake swarm region using a standard least squares technique iteratively.The results show that the structure is obviously inhomogeneous in the middle and upper crust.A low scattering coefficient zone exists at depth of 10~25 km in the central part of research area.This low scattering coefficient zone is surrounded by large scattering coefficient zones at depth of 10 km and 15 km,but the large scattering coefficient zone remains only in the east at depth 20 km.Seven Ms≥6.0 earthquakes in 1997 occurred at the center or edge of the low scattering coefficient zone.