汤西断裂的断层围陷波初步研究

作为断层围陷波方法在城市活断层探测中的首次尝试,我们针对太行山山前断裂带南段的汤西断裂开展了爆炸震源的观测试验。运用数字滤波和频谱分析等技术,由地震记录图分离出了断层围陷波。根据2横测线的观测结果,可确定断层的位置,并可推测断层在该处宽度为200～300m。破裂面较宽,可能与其张性特征有关。分频道地震图显示,断层围陷波具有正频散现象,其低频分量传播较快。这表明断层围陷波是一种面波,可利用其频散规律研究断裂带内介质的物理性质。这次的观测结果也表明,断层围陷波并不局限于新破裂带,在老断层中也能形成和传播。事实上,只要断层带内外的介质在物理性质上有较大的差异,均能产生沿断层传播的围陷波。在城市活断层探测中,断层围陷波的方法具有非常独特的优越性

A PRELIMINARY STUDY ON TANGXI FAULT USING FAULT ZONE TRAPPED WAVES

As the first application of fault zone trapped waves to the active fault exploration in urban areas, an experiment aimed at Tangxi Fault of Taihang Mtns. Fault Belt was performed with explosion sources. By using digital filtering, spectral analysis and other techniques, the fault zone trapped waves were separated from seismograms. Based on the observational data of two transverse profiles, the position of the fault was detected, and its width was assumed to be 200 - 300m. The great width of the fractured zone may be due to the tensional action. The normal dispersion nature of the fault zone trapped waves was revealed from multiple bandpass filtered seismograms. The waves with lower frequencies travel faster than those with higher frequencies. This indicates that the fault zone trapped waves are surface waves and their dispersions can be used to study physical properties of the medium in the fault zone. The results also show that the fault zone trapped waves can be formed and propagate not only in new fractured zones, but also in old faults. Indeed, they can be generated if the physical properties of the mediums inside and outside the fault zone are quite different. The method using fault zone trapped waves is of great advantage for active fault exploration, especially in urban areas.