Strain Evolution Characteristics Before and After Lushan Ms7.0 Earthquake Using GNSS Baseline

Using GNSS data obtained from the Crust Movement Observation Network of China between 2011 and 2014, the GNSS baseline length change time series in the near field of Lushan Ms7.0 earthquake were calculated. From the baseline after planar projection, the solution method of surface strain was proposed. Based on Linear strain, maximum shear strain, maximum surface expansion, the first shear strain and second shear strain, the dynamic evolution characteristic of the crustal movement before and after earthquake was analyzed. The result of the linear strain series shows that the NW-SE compression and S-N extension are reflected.The linear strain anomaly is obvious before earthquake and restore original linear change trend after earthquake, and the whole linear strain is still continuing to accumulate. The result of the surface strain series shows that the strain change trend appeared obvious abnormal deviation before the earthquake. Especially, the stability lock state and reverse acceleration changes is more obvious. The whole change curve is similar to parabola, which agrees well with the deformation theory of rock mechanics. According to the prominent abnormal change of the first shear strain, it's concluded that a strong sinistral shear tectonic forces is generated in south of seismogenic fault.