Pre-Seismic Deformation Related to the Wenchuan Earthquake

  Objectives  Revealing the characteristics of deformation field related to earthquake preparation process is an important way to distinguish earthquake preparation stage and earthquake risk. In order to reveal the significance of crustal deformation observation, the deformation field related to the Wenchuan Ms 8.0 earthquake preparation and the relationship between the deformation field and the seismic activity are discussed from a large spatial scale.

  Methods  The original data of crustal tilt observed at Wenchuan station in the epicenter area of the Wenchuan earthquake since 2002 are collected, and the phased characteristics of crustal tilt change are extracted by using wavelet analysis method and piecewise fitting method. Based on the daily solution data of global navigation satellite system (GNSS) station coordinates since 2001, the baselines between Luzhou station and the surrounding stations are calculated. By comparing the baseline change with the Benioff creep, the synergistic characteristics between them are found.

  Results  The tilt rate in EW direction at Wenchuan station began to decrease significantly at the end of 2004, from 230 ms/a to 130 ms/a, and it decreased to 60 ms/a until the earthquake occurrence. There was no significant exponential acceleration change from the end of 2007 to the earthquake occurrence. The rapidly shortening anomaly of Guangzhou-Luzhou GNSS baseline in early 2005 has a high correlation with the earthquake creep loss anomaly, and the correlation coefficient is 0.89. The duration of rapidly shortening is about 2.5 years, and the magnitude of the corresponding earthquake is estimated to be 7.9, which is close to the magnitude of the Wenchuan earthquake. The Sumatra Ms 8.9 earthquake in 2004 has a significant impact on the stress-strain field in the eastern Tibet Plateau and accelerates the preparation process of the Wenchuan earthquake.

  Conclusions  The different influence of surrounding earthquakes should be considered in the analysis of crustal deformation and earthquake risk. The research results of this paper have reference value for understanding the significance of crustal deformation measurements and innovating earthquake prediction ideas.