美国加利福尼亚州兰德斯和海克特曼恩地区于1992年和1999年先后发生7.4级和7.1级地震,分别在地面产生80km和40km长的断裂带。震后在断裂带布置的密集地震站台记录到明显的断层导波(fault-zone guided waves)。这些导波由断层带内的余震和人工震源激发产生,走时在S波之后,但具有比体波更强的振幅和更长的波列,并具有频散特征。通过对2～7 Hz断层导波的定量分析和三维有限差分数字模拟,获得了震深区断裂带的高分辨内部构造图像以及岩石的物理特性。数字模拟结果表明这些断裂带上存在被严重破碎了的核心层,形成低速、低Q值地震波导。核心破碎带宽约100～200 m,其内地震波波速降为周围岩石的40％～50％,Q值约为10～50。根据岩石断裂力学观点,这一低速、低Q值带可被解释为地震过程中处于断层动态断裂前端的非弹性区(或称之为破碎区,相干过程区)。在兰德斯和海克特曼恩断裂带测得的破碎区宽度与断裂带长度之比约为0.005,基本上符合岩石断裂力学预期的结果。观察到的断层导波还显示兰德斯和海克特曼恩地震中多条断层发生滑移和破碎。兰德斯地震时多条阶梯形断层相继断裂;而在海克特曼恩地震中,断裂带南北两端均出现分枝断裂,深处的分枝断裂较地表出现的破裂状况更为复杂。由三维有限元模拟的动态断裂过程表明,? The 7.4 and 7.1 magnitude earthquakes occurred successively in 1992 and 1999 in the Landes and Hector Mann regions of California, USA, respectively, producing 80km and 40km long fault zones on the ground respectively. After the earthquake, clear fault-zone guided waves were recorded at the intensive seismic stations arranged in the fault zone. These guided waves are excited by aftershocks and artificial sources within the fault zone and travel after the S wave but with stronger amplitude and longer wave train than the body wave with dispersion characteristics. By means of quantitative analysis of 2 ~ 7 Hz guided wave and three-dimensional finite difference numerical simulation, high-resolution internal structural images of the seismic zone and the physical characteristics of the rock are obtained. Numerical simulations show that there are severely fractured core layers on these faults that form low-velocity, low-Q seismic waveguides. The core crushing bandwidth is about 100-200 m. The seismic wave velocity in the core is reduced to 40% -50% of the surrounding rocks, and the Q value is about 10-50. According to the rock fracture mechanics, this low-velocity and low-Q band can be interpreted as the inelastic zone (or crushing zone, coherent process zone) at the front of fault dynamic fracture during the earthquake. The ratio of the width of the crushed zone to the length of the fault zone measured at the Landes and Hatchmann faults is about 0.005, which basically corresponds to the expected results of rock fracture mechanics. The observed guided wave also showed slippage and fragmentation of multiple faults in the Landes and Hector Mann quakes. In the case of the Lancterman Earthquake, multiple faults were successively fractured in the Landers earthquake. In the Hector Mann earthquake, there appeared branch faults at both the north and south ends of the fault, and the ruptures at the deeper branches were more complicated than those at the surface. The dynamic fracture process simulated by three-dimensional finite element shows that