本申请拟从北美西部PBO钻孔应变数据中系统地寻找两类长周期异常应变信号，其中第一类明显与近地表孔隙压力相关，而第二类则出现在中级地震之后。项目拟分析这两类长周期异常应变信号的时间变化和空间分布特性，通过孔弹介质力学数值模拟，建立第一类异常应变信号与降水、孔隙压力变化之间的物理联系，结合GPS观测确定第二类异常应变信号源的位置和属性，分析信号源与地震之间的关系，探讨断层面震后余滑、地震触发其它区域蠕动等可能性，分析地球介质粘弹、孔弹特性等因素对地下应变的贡献。本项目拟研究的这两类长周期应变信号均属学术界首次发现。项目对其起因和物理机制的研究将提出新的物理机制，同时也将提高我们对地球浅表应变变化过程和产生机制的理解，更好地了解近地表各种因素对地表形变的影响。

This proposal proposes to systematically search for two types of long-period anomalous strain signals observed in the PBO borehole strainmeters installed in the Western North America, with one kind of signal related to near-surface pore pressure and the other occurring after some moderate earthquakes. The proposal will analyze the temporal and spatial characteristics of these two types of long-period strain signals, establish a physical relationship of the first type of signal with rainfall and pore pressure changes based on poroelastic theory, determine the location and characteristics of the source for the second type of signal, explore possible mechanisms of fault afterslip and earthquake-triggered creep, and evaluate the contributions of Earth’s poroelastic and viscoelastic effects on near-surface deformation. The investigation of these newly discovered strain signals and their origins will identify new physical mechanisms of near-surface deformation and improve our understanding of near-surface geophysical processes and their controlling factors.