海原断裂带断层通道波观测与破碎带宽度

THE OBSERVATION OF TRAPPED WAVES AND THE WIDTH OF THE SHATTERED ZONE IN HAIYAUAN FAULT ZONE

断层通道波是低速断层破碎带与高速围岩之间的边界相干多重反射形成的,其振幅和频率强烈依赖于断层的几何形态和物理性质,故能用于探测断裂带的内部结构。在宁夏海原西安州附近海原断裂带上,横跨1920年海原8.6级地震地表破裂带布设2条测线,接收测线之间人工爆破激发的断层通道波。每条测线由14台3分量数字地震仪组成,靠近破裂带台间距30～40m,远离破裂带台间距增大至230～250m。对测线1的台站接收到的一炮垂直道地震波数据进行了0.1～4.0Hz频段的滤波,结果表明在S波到时之后存在多组强振幅、低频率、长波链的断层通道波。由断层通道波揭示的海原断裂带在西安州附近的断裂破碎带宽度约为250m。

Two linear seismic arrays are deployed across the surface rupture of 1920 M 8.6 earthquake along Haiyuan fault zone near Xianzhou, Haiyuan County, Ningxia, to receive fault zone trapped waves generated by near-surface explosions within the fault zone between the two lines. Each array consists of 14 three-component portable digital seismic stations, with the interval between two stations being 30～40 m near the fault zone and 230～250 m away from the fault zone. After filtering in a frequency range of 0.1～4.0 Hz, vertical component seismograms on Line 1 show fault zone trapped waves with relatively large amplitude, low-frequency and long-duration wave train after the S waves. Since the trapped waves arise from coherent multiple reflection along boundaries between the lowvelocity fault zone and the high-velocity surrounding rock, their amplitudes and frequencies are strongly dependent on the fault geometry and physical properties. Thus, fault zone trapped waves can be used to explore inner structures of the fault zone. The study of the fault zone trapped waves reveals that the shattereing width of Haiyuan fault zone near Xianzhou is about 250 m.