On the preseismic deformation changes prior to the Lushan M_S7.0 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.