| Two destructive earthquake, Ms8.0 Wenchuan earthquakes in 2008 and Ms7.0 Lushan earthquake in 2013, occurred on in the middle and southern segments of Longmen Shan fault zone locating between Bayan Kala block and South China block just in five years, making this area one of the most important earthquake areas to be researched, long-term ground movement monitor and earthquake risk prediction for this area is needed. Five years’ data from ten continuously operating GPS stations in Longmen Shan fault zone south were used in this research, and some post processing methods were adopted to process the GPS displacement time series, such as Euler Conversion, Least Squares Collocation, Quasi-Accurate Detection of gross errors, Block Rigid and Elastic-plastic Model, Bessel Geodetic Inverse Solution Method, and Negative Dislocation Model, to obtain displacement time series and station velocity in East China Datum, and block strain parameters, geodetic baseline time series, locking and slip deficit value on Lushan seismogenic fault.These deformation parameters were used to analyse the crustal movement of the area in Longmen Shan south crossing 29.5°N~31.5°N and 101.5°E~104°E, mainly the ground movement change, earthquake risk in sub-areas caused by Wenchuan earthquake, influencing range and intensity of Whenchuan earthquake in the area, and how Wenchuan earquake effected Lushan seismogenic fault and locking and slip deficit value on it. The major conclusions were as follows:(1)Influence of Wenchuan earthquake in Longmen Shan south became low from its northwest to southeast, the maximum ground displacement and velocity in the northeast during five years after Wenchuan earthquake was 100 mm and 20mm/a which was six times of the velocity before the earthquake. Displacement of the nearest station from Wenchuan earquake center in the southeast was only 30 mm, and velocity was 9mm/a.(2)Seismic risk in the west of Longmen Shan was low, where the ground velocity, area strain rate and shear strain rate were large, the largest area strain was 2010 /a in the area just south of Wenchuan earthquake center near Wenchuan-Maoxian fault, where the geodetic baseline shortening rate was 9mm/a and deformation space was large. While the seismic risk near Guanxian-Anxian fault was high, where the ground deformation space was small, the ground velocity, strain rate were low, area strain rate was 5 10 /a, and the geodetic baseline shortening rate was 0.8mm/a.(3)Locking value of Lushan seismogenic fault above the depth of 22 km was high before Wenchuan earthquake, while the creep zone expanded to a 20-24 km deep and 50 km long area with low locking value but stable shape in the south of Wenchuan earthquake source.(4)Slip deficit rate in the parallel direction of Lushan seismogenic fault had low influence from Wenchuan earthquake, while the normal direction was great. Slip deficit rate in the normal direction was 12.5mm/a during 2007 and 2009, which was three times of that before the earthquake at least. The normal direction slip deficit rate decreased ever since, which was 5.8mm/a near the Lushan earthquake source, and increased to 7.0mm/a to the Wenchuan earthquake source along Lushan seismogenic fault two years before Lushan shaked, but was still larger than that before Wenchuan earthquake. Large slip deficit rate in the normal direction of Lushan seismogenic fault caused more compressive strain on it, while the normal silp deficit rate was slowest near Lushan earthquake source, which had the smallest strain area and was the most dangerous area on the seismogenic fault.(5)Wenchuan earthquake released some compressive strain on the east of Xianshuihe fault south, but with the effection of sinistral strike-slip of Chuandian block, this area regained compressive rate just as that before Wenchuan earthquake. |
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