摘要
由三分向数字地震仪构成的小孔径流动台网记录了1989年10月山西大同二个强震之后15天内的余震。纵波和横波的尾波在直达波的后续波列中表现得非常明显,估计是由近地表不规则沉积层对地震波的聚焦效应所形成的。由于近地表不规则沉积层的作用,在较宽的离源角的范围内都可以辨认出横波分裂现象。用大范围膨胀各向异性(EDA)裂隙对横波的影响解释了快波偏振的排列方向与区域应力场最大主压应力方向的一致性。对一天中包括一个较大地震以及它前后较小地震形成的系列,用理论到时差数值模拟与实际记录对比的方法,确认了横波分裂到时差在一个较大地震发生前后的上升和下降,用应力导致壳内裂隙随时间的变化对横波传播的作用解释了这种变化。到时差在短时间内发生的迅速变化说明含有EDA裂隙的上地壳对区域应力变化具有快速的弹性响应。
The aftershocks over 15 days after two large earthquakes, in October 1989 in Datong Area, North China, were recorded by temporal small apertural network consisted of three component digital seismographs. P-wave codas are remarkable feature of P-wavetrains and are expected to be caused by concave sediment layer and transit layer under stations. Shear wave splitting could be identified in the wider range of take-off angles for this particular near-surface structures. Polarizations of faster shear-waves have the alignment consistent with the direction of nearly horizontal regional maximum compression. The relative delays for two sequences of foreshock, mainshock and aftershock during one day are further recog-nized as being quickly variations before and after the significant events, using the method of comparing theoretical calculation and the observation records. This phenomenon could be in-terpreted in term of EDA-cracks and its temporal changes induced by changes of regional stress. The variation of relative delay in short time interval illustrated the faster response of EDA-crack of upper crust to the changes of regional stress.
出处
《华北地震科学》
北大核心
1992年第3期12-26,共15页
North China Earthquake Sciences
