西昆仑山前构造带地震变形特征的InSAR/GPS研究—以皮山地震为例

Because subjected to the persistently converge and wedge between India and Eurasian plate, the border of Tibetan Plateau usually occurred large devastating earthquakes in its frontal region, such as the 2008 Wenchuan Ms 8.0 earthquake and 2015 Nepal Ms 8.1 earthquake. As one of the most important border in the Tibetan Plateau, the western Kunlun tectonic region locates in the northwest boundary, where is remarkable whether an earthquake risk with magnitude of Ms 8.0 will occur in the future. However, due to the severe environment and scarce observation, the regional geological setting is not well known..The 2015 Pishan Mw 6.4 earthquake which justly occurred along the western Kunlun Shan, providing a rare chance to gain insights into the interaction between the Tarim Basin and the Tibetan Plateau, and the growth of the Tibetan Plateau. In this proposal, to overcome the disadvantage of planar fault used in slip inversion for a blind fault, we take account of seismic profile to construct a more accurate listric fault to inverse the coseismic slip for Pishan earthquake. After that, by combining the GPS data from several postseismic campaigns, we use the time series InSAR with high precision to obtain the postseismic displacement for Pishan earthquake, then recognize the postseismic mechanisms and analyze the relationship between postseismic response and coseismic rupture. Finally, we assess the risk of regional strong earthquake by researching the seismic activity habit and rupture model in the front foothill of western Kunlun. The project will be helpful to promote the sustainable development of the research of the tectonic activities and dynamic evolution at the north border of Tibetan plateau.

受印度板块对欧亚板块持续向北的碰撞与挤压楔入作用，青藏高原边界前缘区往往会产生大的破坏性地震，如2008年汶川Ms 8.0地震和2015年尼泊尔Ms 8.1大地震。作为青藏高原块体西北缘的重要边界带，西昆仑山前构造带是否存在8级地震的危险性，非常值得关注。. 2015年Mw 6.4皮山地震，恰好位于西昆仑前缘逆冲活动带，为我们认识该区域构造活动、理解青藏高原隆升机制提供了契机。考虑平面滑动断层几何在山前隐伏构造研究中的不足，本项目在顾及地震反射剖面资料的基础上，构建更为精细的铲式断层几何反演此次地震的滑动破裂。同时在已有多期震后GPS观测的基础上，利用高精度时序InSAR技术研究皮山地震的震后时序变形，反演震后变形机制，分析震后变形与主震破裂的关系。最后通过山缘构造地震活动习性及破裂方式研究评估区域强地震危险性。本项目将有助于推动青藏高原西北边界带构造活动及动力学演化研究的持续发展。

随着山缘地带人口快速增长，社会、经济活动日趋频繁，灾害效应急剧扩大，一旦地震降临，伤亡格外惨烈。在2008年汶川地震和2015年尼泊尔大地震后，青藏高原块体西北缘边界带是否具有孕育8级地震的危险性受到广泛关注。本项目在前期对皮山地震的研究基础上，开展了山缘区域中强地震破裂机制、皮山地震的震后形变时空响应、和区域地震串丛触发的探索研究。研究内容涉及同震变形及破裂模型构建，大地测量与地震波的联合反演，三维同震形变场的提取，高精度时序InSAR信号分析，震后形变机制建模等。厘定了若干山缘中强地震的震源机制，空间大地测量观测能为真实的断层几何破裂识别提供有效约束，丰富对山缘构造活动的认识；多源数据观测有利于改善地球物理反演的不确定性，获取多维的地下结构的运动学和动力学信息，联合大地测量与地震波观测开展了地震破裂几何和动态破裂过程的研究，应用于Anchorage、Ezelegh和皮山地震；形成了一套高精度三维形场构建的技术方法；时序InSAR研究结果表明皮山震后恢复过程持续了2.5年，最大形变量4 cm，发现明显地地壳运动非线性时变细节特征，对确定区域的应力摩擦研究提供了重要的约束；基于库仑应力研究推断于田若干次地震具有级联触发，但是震间GNSS确定的震间应力累积小于这些地震释放的总地震能量，从而表明西昆仑东边界于田地区的拉张活动存在深部过程响应。依托项目资助共发表高水平研究论文12篇，培养研究生3名，研究成果为深入区域灾害研究提供了较好的科学基础。