Possible Precursory Observations Relevant to the 2013 Lushan Ms7.0 Earthquake, China

Abstract:

The 2013 Ms7.0 Lushan earthquake is the strongest event occurred along the Longmen fault following the 2008 5.21 M8 Wenchuan earthquake in China. Based on the a couple of deformation measurements on the surface, including cross-fault baseline, leveling, tilt, strain, gravity and continuous GPS data, we analyze the spatial and temporal characteristics in surface deformations before the Lushan earthquake. The results indicate that (1) since January 2013, significant accelerating compression can be seen from the cross-fault baseline deployed along the Xianshuihe fault; (2) anomalies in the time series of leveling and cross-fault baseline are observed at several sites along Anninghe and Zemuhe faults; (3) most of the leveling records cross the Longmenshan fault with small variations, have the indication of earthquake precursors; (4) the horizontal and vertical GPS displacement rates in the near field are smaller than those in the far field, suggesting there existing a weak area in the source region without significant changes in surface deformation; (5) the annual amplitudes of tilt and gravity in the near-field, extracted by the Fourier transform, are smaller in 2-3 years before the Lushan event. All of these observations can improve our understanding on earthquake nucleation process.