Effect of long-term surface temperature variation on fault displacement observation and anomalous fault movement in Western Sichuan before the Lushan M_s7.0 earthquake
About 2—3 years before the Lushan Ms7.0 earthquake on 20 April 2013,some shortbaseline and short-leveling sites in western Sichuan presented long-term and quasi-synchronous trend transition.However,the temperatures from some auxiliary observation were similar to fault displacements in some extent.So,in order to explore if they are thermal deformation,we analyze the short-baseline,short-leveling,and temperature observation data from Xianshuihe,Anninghe-Zemuhe,and Longmenshan fault zone.Based on spectrum and statistical analysis methods,the correlation between fault displacement and temperature is studied.Furthermore,the movement features of these fault zones are discussed by using principal mode analysis.The results show that:(1) In the period of larger than 2.63 years,the fault displacement and temperature data have similar frequency components,and have weak to moderate correlation.(2)The variation of temperature is not the major influence factor on the trend transition of fault displacement before Lushan earthquake.Except individual site,the secular thermal deformation only contributes a small fraction in the whole deformation.(3) The principal mode analysis suggests that,around 2010,the left-lateral strike slip and tensional movement weakened along Xianshuihe fault zone,and the tensile motion of Anninghe-Zemuhe and Longmenshan fault zone weakened also.These variation features may be associated with the intensive movement in SESEE orientation of the Bayan Har tectonic block in this stage.