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横跨龙门山断裂带南段的连续GPS测网记录到了2013年4月20日芦山MS7.0地震孕育过程相关的地壳变形信息,为研究此次地震前孕震区地壳变形动态演化过程提供重要的基础资料.研究表明,汶川地震的发生导致茂县-汶川断裂南段及以东地区挤压应变和左旋剪切应变加载.GPS跨单条断裂的基线平均缩短速率约为1~2 mm/a,跨越整个断裂带的基线平均缩短速率约为8~10 mm/a,且均表现出随芦山地震临近年均缩短速率逐渐减小的特征;多站组合的应变参数时序结果显示,龙门山断裂带南段主压应变率自西向东逐渐减小,主压应变方向为N30°~45°W近似垂直于断裂带;北川-映秀断裂以东地区以挤压变形为主兼有明显的左旋剪切变形,且面应变和第一剪应变随着芦山地震的临近应变率逐渐减小;北川-映秀断裂以西则表现为在时间进程上逐渐增强的右旋剪切变形.区域GPS变形场结果显示汶川震后龙门山断裂带南段挤压应变积累速率显著大于震前,且茂县-汶川断裂以东地区表现出左旋剪切应变积累特征.综合分析认为,汶川地震后巴颜喀拉块体东向运动加速,运动速度自西向东递减,致使在汶川地震中未破裂的龙门山断裂带南段的挤压应变积累水平进一步增强.
The continuous GPS network across the southern segment of the Longmenshan fault zone recorded crustal deformation information related to the gestation process of the Lushan MS7.0 earthquake on April 20, 2013, which is important for studying the dynamic evolution of crustal deformation in the seismogenic zone before the earthquake The results show that the occurrence of Wenchuan earthquake resulted in the compressive strain and the left-lateral shear strain loading in the southern segment of the Maoxian-Wenchuan fault.At the same time, the average baseline shortening rate of GPS over a single fault is about 1 ~ 2 mm / a, The average baseline shortening rate across the fault zone is about 8-10 mm / a, and both show a decreasing trend along with the annual average shortening rate of the Lushan earthquake. The time series of the strain parameters of the multi-station assemblage shows that the Longmenshan fault zone The principal compressive strain rate in the southern section decreases gradually from west to east, and the principal compressive strain direction is N30 ° ~45 ° W, which is approximately perpendicular to the fault zone. In the area to the east of Beichuan - Yingxiu fault, compressive deformation is dominant with obvious left-hand shear Deformation, and the surface strain and the first shear strain decrease gradually along with the Lushan earthquake. The westward of the Beichuan-Yingxiu fault shows the dextral shear deformation that gradually increases in time course. After the earthquake, the accumulation rate of compressive strain in the southern segment of the Longmenshan fault zone was significantly larger than that before the earthquake, and the accumulation of left-lateral shear strain in the eastern area of the Mao-Wenchuan fault showed that the eastward direction of the Bayan Har block The acceleration of the movement and the decrease of the velocity of the movement from west to east resulted in the further increase of the compressive strain accumulation in the unbroken Longmenshan fault zone in the Wenchuan earthquake.