【摘要】 通过对 1997年 5月 10日Zirkuh (Ghaen Birjand )破坏性地震若干余震横波分裂现象的观测 ,研究了该地区上地壳各向异性特征 .采用质点运动图和纵横比两种不同手段获取了横波分裂参数 .所选余震记录显示了明显的横波分裂 ,说明该地区介质具有强烈的各向异性 .通过质点运动的方法得出 :快横波的偏振方向为 2 2°N± 19°E ;且快、慢横波的延时之差为 6 5± 16ms .用纵横比的方法得到的结果为 :快横波的偏振方向 35°N± 18°E ,且快、慢横波的延时之差为 (4 9± 10 )ms .对于厚约 5km各向异性均匀分布的水平层 ,我们采用了一个沿应力分布的裂纹模型 ,并采用垂直于N2 2°E排列 ,且密度为 0 .0 1的裂纹情况来解释本文结果 .由于研究范围是上地壳 ,因此假设裂纹被水填充 .最后通过Hudson模型 ,对裂纹密度为0 .0 0 5 ,0 .0 1和 0 .0 3的模型 ,给出横波速度随传播方向与裂纹对称轴夹角的变化曲线 .结果表明 ,当横波的偏振平行于裂纹表面时波速不随角度变化 ;而偏振垂直于裂纹表面时 ,速度曲线则有明显变化 .更多还原

【Abstract】 A number of aftershocks of the May 10th 1997, Zirkuh (Ghaen-Birjand) destructive earthquake have been used to investigate the anisotropy in the upper crust by observing shear wave splitting. Particle motion diagram and aspect ratio methods were used as two different approaches to obtain splitting parameters. Clear shear wave splitting was observed on the records of the selected aftershocks, indicating that the media in the region was highly anisotropic. By using particle motion method, the direction of fast shear wave was found 22°N±19°E, while the delay time between the fast and slow shear waves was obtained to be (65±16) ms. By aspect ratio method, the direction of fast shear wave was determined to be 35°N±18°E and the delay time between fast and slow shear waves was found to be (49±10) ms. For a simple horizontal layer with a thickness about 5 km and uniformly distributed anisotropy, a stress aligned cracks model was used and the result was interpreted in terms of vertical aligned cracks in the direction of N22°E, having a density about 0.01. It is assumed that cracks are fluid-filled since they are located in the upper crust. Finally, by using Hudson cracks model for three crack densities 0.005, 0.01, 0.03, the velocity curves of shear wave were plotted as a function of angle between the symmetrical axis of cracks and the azimuth of source to receiver. It was concluded that when shear wave was polarized parallel to the crack surface, the velocity was uniform, but the velocity curve varied clearly if shear wave was polarized perpendicular to the crack surface.更多还原