芦山MS7.0地震前远、 近场形变 时空演化特征研究

应用芦山M_S7.0地震震中附近跨断层及连续形变观测资料， 分析了芦山地震前不同阶段地形变变化的特点， 讨论了震中附近区域异常时空演化过程. 结果表明: ① 自2013年1月起， 沿鲜水河断裂带一些跨断层基线观测到显著的加速转折变化, 沿安宁河、 则木河断裂带个别场地的跨断层水准基线， 2010年以来出现的巨幅异常等是突出的场兆变化； 沿龙门山断裂带一些水准观测在汶川M_S8.0地震后持续的调整变化具有近震源区变形特征. ② 鲜水河、 龙门山和安宁河3条主要断裂围成的三叉口地区， 地倾斜、 应变、 重力及断层水准和蠕变观测临震前均未有显著的异常变化， GPS水平、 垂直位移年速率最小， 该地区是形变变化或形变异常分布的“空区”. ③ 在对近场与远场多种连续形变数据通过傅里叶变换提取年周期成分后发现， 临震前2—3年近震源区域的地倾斜、 重力年变化幅度不是增大， 而是减小. 芦山M_S7.0地震前观测到的形变前兆现象特征与汶川M_S8.0地震等震前的前兆现象较为接近. 因此， 芦山地震前近震源区及外围形变异常分布特征不是个别的现象. 

On the preseismic deformation changes prior to the Lushan MS7.0 earthquake

This paper analyzes and discusses the spatio-temporal evolutionary characteristics of deformation prior to the Lushan M_S7.0 earthquake, based on the data of cross fault and continuous deformation measurements near the epicenter of the earthquake. The results show that: ① the cross fault baseline length has been significant acceleration-turning at some cross-fault sites along the Xianshuihe fault since January of 2013, and some anomalies of leveling and baseline lengths recorded at individual sites along Anninghe and Zemuhe faults are the field precursors. Small adjustment of most of the leveling cross the Longmenshan fault presented the characteristic of source precursors. ② In the cross connected area of the Xianshuihe, Longmenshan and Anninghe faults, no significant anomalies were recorded by means of continuous deformation (tilt, strain, gravity), fault leveling, and creep observation. Moreover, the GPS horizontal and vertical velocities nearby the source are smaller than the outer region, so there is a concept of Weak Area, where no significant changes in deformation or no anomalies. ③ The annual amplitude of tilt and gravity in the near-field, extracted by the Fourier transform, is reduced 2—3 years prior to the event, which is our newly understanding about the earthquake precursors. The results mentioned above indicate that the precursory phenomena before the Lushan M_S7.0 earthquake, observed by deformation measurements, are similar to those before Wenchuan M_S8.0 and so on, so it is not individual.