西藏亚东-谷露地堑分段滑移速率的GPS/InSAR监测与构造意义

A lot of large scale SN-trend rifts distributed in the Tibet plateau. Those rifts have played a very important role during the evolution of tectonics in the Cenozoic Era. Also, it is a key point for the topographic changes, tectonic block movements and the seismic activities. But the lack of quantified descriptions of seismic geology and geodesy in this area makes it very limited to understand the adjustment role of those faults how to shorten along SN and how to extend along WE within the plateau in the Quaternary. This study is focused on the 500km-long Yadong-Gulu rifts which stretches over the Yaluzangbu suture zone. GPS and InSAR will be used to monitor the crustal deformation and to derive an accurate 3-d velocity map of the area. We expect to densify the existed GPS network and form several profiles across the rift and then to integrate the GPS and InSAR measurements to derive the velocity maps and geometry of different segments of the rift, cooperated with geology and geophysics data. Finally, we will inverse the lock depth of different segments and investigate the relationship between crustal deformation features and strong earthquakes as well as relationship between the lock depth and deep struture. It will help us to best understand the characteristics of Yadong-Gulu rift and to clarify the role of rifts in central and southern Tibet played in the evolution of Tibet Plateau in the Quaternary.

大量分布的南北向大型地堑（裂谷带）在青藏高原新生代构造演化中发挥过重要作用,是制约高原地形地貌、构造块体运动及强震活动等的控制因素,但由于断层活动定量化的地震地质和大地测量数据等关键资料的不足,对这些断层在第四纪青藏高原南北向缩短、东西向伸展变形过程中的调节作用仍认识有限.本研究拟以横跨雅鲁藏布江缝合带,500公里长的亚东-谷露地堑为对象，开展GPS、InSAR监测,通过加密观测，建立数条跨断层的地壳位移速度剖线,结合该地区已有的地震地质及地球物理资料，将GPS与InSAR融合,精确测定亚东-谷露断裂带各段的运动速率、几何学特征,并反演计算断裂带各段的闭锁深度，研究该断裂带构造活动特征及其与强震的关系,探索断层闭锁深度与深部构造活动的关系,揭示亚东-谷露地堑的构造意义，以澄清青藏高原中南部地堑在青藏高原第四纪构造演化的地位。

以500公里长、近南北向的亚东-谷露裂谷带为对象，沿裂谷带及周边地区，进行了GPS测点的加密埋设和观测，结合该地区的其他GPS观测，获得了该地区较为密集的GPS水平形变场，同时利用InSAR技术获取了该地区的LOS形变速度场，分别采用GPS和InSAR形变场对亚东-谷露断裂带各段的运动速率、几何学特征及闭锁深度进行了研究，最后基于历史地震目录和地震应力触发理论，采用岩石圈地壳分层粘弹性位错模型，计算了尼泊尔Mw7.9地震对亚东-谷露及周边活动断裂的同震和震后库仑应力变化．结果表明：.1）.沿亚东谷露裂谷带，GPS速度场大小由南往北逐渐减小，运动方向由南往北，在经过雅鲁藏布缝合线后，方向逐渐往东向偏转，存在顺时针转动的特征；.2）.沿亚东-谷露断裂带，GPS的水平形变场，由南往北平均变化(线性拟合)范围为28.0mm/yr~24.3mm/yr，幅度较小；GPS的南北向形变场，由南往北平均变化(线性拟合)范围为25.4mm/yr~11.6mm/yr，变化幅度为-13.8mm/yr；GPS的东西向形变场，由南往北平均变化(线性拟合)范围为12.7mm/yr~22.1mm/yr，变化幅度为9.4mm/yr；表明沿亚东-谷露断裂带的地壳运动，南北向压缩，东西向拉张，NS和WE方向的应变率分别为-2.4*10^-8/yr和4.9*10^-8/yr，地壳运动以拉张为主；.3）.沿雅鲁藏布缝合线南北两侧的地壳运动，呈现为线性运动，差异运动不明显表明雅鲁藏布缝合线作为印度板块与欧亚板块碰撞的界线，其现今的地壳运动处于较弱的活动状态。通过欧拉矢量，获得了雅鲁藏布缝合线的滑移速率，西段右旋速率为4.5mm/yr，东段为2.2mm/yr；亚东-谷露裂谷带南段的拉张速率约为6.75±0.9mm/yr，北段的拉张速率为4.72±0.8mm/yr，其中南段的结论与Chen et al.(2004)的结果6.6 ± 2.2 mm/yr基本一致；亚东-谷露裂谷带闭锁深度为10公里。.4）.受制于误差影响和LOS对三维形变的敏感性，由InSAR获得亚东-谷露裂谷带各段的滑移速率较小，闭锁深度也较大；.5）.尼泊尔地震的同震效应引起亚东-谷露断裂南段应力的持续增强，地震活动性值得进一步关注。