摘要:
本文描述了一个解时空反演问题的方法.通过把华北地区看成是由24条主要断裂带组成的地质构造骨架,在15公里深处按照平面应变的理想塑性体处理,用有限单元方法计算了本地区在均匀边界外力作用下发生地震危险的地带.然后用逐次降低断层内摩擦系数的办法,模拟近十二年来历次大地震,计算释放应力后应力场的变化、断层的错动.将计算结果和实测资料进行对比,对各个力学参数和构造骨架进行了多次修改,使它们尽量接近.结果说明本方法能够基本上重复近十二年来的地震迁移规律,并可望对未来的地震危险区提出参考意见.结果还说明地震以后在沿断层错动方向的左前方有一狭窄扇形地带安全度增加,而其余较大地区由于断层处的应力释放使剪破裂的危险度有些增加.
Abstract:
Paper describes a certain process of solving a space-time inversion problem. A certain North China region is treated as a grillage of tectonic structures composed of 24 major faults and as an elastic-ideally plastic body in plane strain at a depth of 15 km. It is subjected to uniform stress along the boundaries. By means of the finite element method, the stress field is calculated and the zones of seismic risk are delineated in this region. By reducing the coefficient of friction in a fault from static to kinetic, stress and strain energy may be released there. Five major earthquakes in the last 12 years in this region are simulated in this manner. By comparing the stress fields before and after the stress release, one obtains the change in strain energy, fault offsets, areas of seismic risk etc. They are compared to data from actual measurements. If they don't agree well, tectonic framework, parameters of mechanical properties and external stress field are adjusted until they do.The results show that the present method can reproduce in essence the pattern of seismic transference in the last 12 years and may give some idea about the zones of seismic risk in the future. They also suggest that, after an earthquake, there are narrow sectors in the left-frontal part along the slippage directions that become safer than before, while in the remaining parts the danger of shear fracture increases.
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