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利用中国地震局地球物理勘探中心 1 998年在伽师地震区记录的天然地震资料 ,通过地震记录波形资料的衰减来反演伽师地震区地壳介质的三维 S波 Q值结构 ,并初步了解该地震区内地壳深部断层的大致形态 .首先 ,对精选的 45 0多次地震记录的 S波求出其振幅谱 ,称为观测振幅谱 ;然后 ,假设震源符合布伦圆盘位错模式 ,在对仪器和场地效应校正之后 ,用非线性阻尼最小二乘法对理论振幅谱和观测振幅谱进行拟合 ,从而得到观测吸收特征时间 ;最后 ,利用三维射线追踪方法 ,对理论吸收特征时间与观测吸收特征时间进行非线性阻尼最小二乘拟合 .在拟合过程中 ,速度模型保持不变 .速度模型是通过三维走时层析成像得到的 ,只修改 Q值模型 ,当拟合达到给定精度后 ,便得到最终的 Q值模型 .结果表明 ,在 1 0～ 1 8km的深度范围内 ,存在一个北东向的低 Q值条带 ;在 1 2～ 1 8km的深度范围内 ,存在一个北西向的低 Q值条带 .这与他人所做的北东向、北西向的两个低速条带较接近 .不同的是 ,低 Q值条带深度范围比低速带的更大一些 .
Based on the natural seismic data recorded by Geophysical Exploration Center of China Earthquake Administration in Jiashi area in 1998, the 3D S-wave Q-value structure of crustal medium in Jiashi earthquake area was retrieved by the attenuation of seismic record waveform data. The general shape of the deep fault in the crust of the earthquake area is first of all described.Firstly, the amplitude spectrum of the S-wave of the selected 45 0 seismograms is obtained, which is called the observed amplitude spectrum; then, assuming that the source conforms to the Brun disc dislocation pattern, After the correction of instrument and site effects, the theoretical amplitude spectrum and the observed amplitude spectrum were fitted by nonlinear damped least square method to obtain the observed absorption characteristic time. Finally, by using the three-dimensional ray tracing method, the theoretical absorption characteristic time and observation Absorption characteristics of time non-linear damping least squares fit in the fitting process, the velocity model remains unchanged speed model is obtained by three-dimensional traveltime tomography, only modify the Q value model, when the fit reaches a given accuracy The final Q value model is obtained.The results show that there exists a northeast low Q band in the depth range of 10 ~ 18 km, Within a depth of 8 km, there is a northwestward low-Q band, which is closer to the northerly and northwesterly bands of low-velocity bands made by others, except that the low Q-band depth range ratio Larger number of low-speed zone.