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研究了发生在一条断层的端部,且靠近引张区一侧的地震,或发生在右(左)旋向右(在)错开的两条雁列型断层的交错部位的地震的震源机制的特点,发现走滑型地震和倾滑型地震兼而有之,但是总的看来它们比发生在主断层上的地震具有较大的倾滑分量。用在无限大平板中含有一条裂纹的平面应力模型,计算了一条二维裂纹附近的应力场,结果表明,局部最大主应力相对远场主应力旋转了5～15°。估计了次生剪切裂纹可能出现的范围,表明它们主要集中在裂纹端部表现为引张的区域内,其取向或者和主裂纹大致平行,或者接近分叉张裂纹的方向。这些裂纹面上的附加正应力为张应力,并且当它们的取向接近张裂纹取向时数值较大,所以,如果地震是由接近张裂纹的剪切裂纹引起的,其震源机制应具有较大的倾滑分量,反之,如果地震与大致平行于主裂纹的剪切裂纹有关时,震源机制的走滑分量应占优势。
The focal mechanisms of earthquakes that occur at the ends of a fault and near one side of the extension zone, or at the staggered parts of two geesetrct faults that occur to the right (left) and to the right (in) It is found that both the strike-slip earthquake and the dip-slip earthquake combine to have larger slip-dip components than the earthquakes occurring on the main fault. Using a plane stress model with a crack in an infinite flat plate, a stress field near a two-dimensional crack is calculated. The results show that the local maximum principal stress rotates 5 ~ 15 ° with respect to the far-field principal stress. Estimating the range of possible secondary shearing cracks indicates that they are mainly concentrated in the area where the crack ends appear as an extension and the orientation is either approximately parallel to the main crack or close to the direction of the bifurcated crack. The additional normal stresses on these cracked surfaces are tensile and their values are large when their orientation is close to the tensile crack orientation. Therefore, if the earthquake is caused by a shear crack near the crack, the focal mechanism should have a larger On the other hand, if the earthquake is related to the shear crack roughly parallel to the main crack, the strike-slip component of the focal mechanism should be dominant.