This paper presents the coseismic displacement and preseismic deformation fields of the Lushan MS7.0 earthquake that occurred on April 20,2013.The results are based on GPS observations along the Longmenshan fault and within its vicinity.The coseismic displacement and preseismic GPS results indicate that in the strain release of this earthquake,the thrust rupture is dominant and the laevorotation movement is secondary.Furthermore,we infer that any possible the rupture does not reach the earth’s surface,and the seismogenic fault is most likely one fault to the east of the Guanxian-Anxian fault.Some detailed results are obtainable.(1)The southern segment of the Longmenshan fault is locked preceding the Lushan earthquake.After the Wenchuan earthquake,the strain accumulation rate in the southeast direction accelerates in the epicenter of the Lushan earthquake,and the angle between the principal compressional strain and the seismogenic fault indicates that a sinistral deformation background in the direction of the seismogenic fault precedes the Lushan earthquake.Therefore,it is evident that the Wenchuan MS8.0 earthquake accelerated the pregnancy of the Lushan earthquake.(2)The coseismic displacements reflected by GPS data are mainly located in a region that is 230 km(NW direction)×100 km(SW direction),and coseismic displacements larger than 10 mm lie predominantly in a100-km region(NW direction).(3)On a large scale,the coseismic displacement shows thrust characteristics,but the associated values are remarkably small in the near field(within 70 km)of the earthquake fault.Meanwhile,the thrust movement in this70-km region does not correspond with the attenuation characteristics of the strain release,indicating that the rupture of this earthquake does not reach the earth’s surface.(4)The laevorotation movements are remarkable in the 50-km region,which is located in the hanging wall that is close to the earthquake fault,and the corresponding values in this case correlate with the attenuation characteristics of the stra
A continuous GPS array across the southern segment of the Longmenshan fault zone recorded the deformation during the process of the Lushan MS7.0 earthquake that occurred on April 20, 2013. Such data can provide meaningful information regarding the dynamic evolution of crustal deformation in the seismogenic zone. Our studies have shown that the occurrence of the Wenchuan earthquake led to the loading of compressive and sinistral shearing strain on the southern segment of the Maoxian-Wenchuan fault, whereby the extrusion strain accumulated at a greater rate than before the Wenchuan earthquake. The strain time series in the seismogenic zone revealed that the principal compression strain rates decreased from west to east in the direction of N30°–45°W. Furthermore, the area to the east of Beichuan-Yingxiu fault behaved as a zone of compressive deformation with obvious sinistral shearing deformation. The surface strain and the first shearing strain time series decreased with time, while the area to the west of the Beichuan-Yingxiu fault behaved as a zone of dextral shear deformation that increased with time. Furthermore, the regional deformation field before the Lushan earthquake showed that the rate of extrusion strain accumulation in the southern segment of the Longmenshan fault zone was obviously larger than before the Wenchuan earthquake. Moreover, the sinistral shearing strain accumulated in the area of the southern segment of the Maoxian-Wenchuan fault. Based on the above analysis, we consider that the eastward movement of the Bayan Har block increased considerably following the Wenchuan earthquake, which enhanced the accumulation of compression strain in the southern segment of the Longmenshan fault zone.
LIU XiaoXiaWU YanQiangJIANG ZaiSenZHAN WeiLI QiangWEI WenXinZOU ZhenYu
