青藏高原西北部区域地壳形变、构造地貌与孕震构造模型研究——以2008年与2014年新疆于田7.3级地震为例

Regional Crustal Deformation, Tectonic Geomorphology and Seismogenic Tectonic Model of the Northwestern Tibetan Plateau:Case Studies of the 2008 and 2014 Yutian (Xinjiang) MS7.3 Earthquakes

摘要:

为了清晰认识发生于青藏高原西北部2008年与2014年的两次于田M_S7.3地震发震构造环境与构造地貌特征,本文利用DEM(数字高程模型)数据分析"喀喇昆仑-西昆仑-康西瓦地区"的地形地貌特征,结合区域活动断裂研究资料、相对于塔里木盆地的两期GPS速度场资料和区域运动学特征等讨论两次M_S7.3地震所处的青藏高原西北部区域构造环境和地壳运动学特征,分析喀喇昆仑断裂、阿尔金断裂康西瓦段、龙木错-邦达错断裂及贡嘎错断裂所围限的西昆仑地块的地质构造背景、阿尔金断裂西南端发震断裂活动性及孕震环境等发震构造基本条件;进而利用"地形剖面"方法及断裂分布特征分析震源区的地形地貌特征,给出晚第四纪以来的地貌形态与发震构造的关系,从区域构造地貌学和GPS地壳运动学的角度探讨中上地壳变形特征及孕震过程;最后讨论区域孕震构造、克尔牙张性裂谷演化过程和地球动力学背景等。通过地形剖面及区域地貌综合分析新疆于田2008年M_S7.3拉张型发震构造和2014年M_S7.3走滑拉张型地震的发震构造特点的区别,认为2014年发生的地震可能与2008年M_S7.3地震同震库伦应力变化、触发过程及震后变形过程密切相关,并且青藏高原西北部地区存在明显的东西向拉张性构造单元,可能与青藏高原10~15 Ma以来的地壳减薄过程有关。

Abstract:

To understand clearly the geomorphologic characteristics and seismogenic structure of the Yutian M_S7.3 earthquakes of 2008 and 2014, the regional tectonic geomorphic features of the Karakoram-Western Kunlun-Kangxiwa region are analyzed using digital elevation model data. The tectonic environment and crustal kinematics of the northwestern Tibetan Plateau, where the earthquakes occurred, are discussed by combining data on active faults and GPS velocity field relative to the Tarim rigid block. The geological background of the Western Kunlun block, which is surrounded by the Karakoram, Kangxiwar, and Longmu Lake-Bangda Lake faults, is discussed. The seismic activity and seismogenic environment of the southwestern segment of the Altyn Tagh fault are studied. In this study, the topographic and tectonic geomorphologic characteristics near the seismogenic region are analyzed using terrain profiles to reveal the relation between the regional geomorphologic characteristics and the seismogenic structure. The deformation characteristics and seismogenic process of the middle and upper crusts are discussed on the basis of the regional tectonic geomorphology and crustal deformation obtained from the GPS velocity data. Finally, the evolutionary process of the Kerya River extension rift and geodynamic background is discussed. It is suggested that the 2014 Yutian M_S7.3 earthquake was related to the coseismic static Coulomb stress and lower-crust viscoelastic relaxation that were part of the post-seismic processes of the 2008 Yutian M_S7.3 earthquake. Moreover, the occurrence of these earthquakes may be related to the crustal thinning of the Tibetan Plateau.