摘要
青藏高原快速隆升过程中,在东西向伸展作用下冈底斯造山带内发育了一系列近南北向的裂谷.其中申扎裂谷及其附近地区历史地震活动频繁,蕴藏了大量的矿产资源.对申扎裂谷及周围区域进行浅层精细结构研究,有助于深入了解裂谷的内部形态,对于理解东西向伸展作用的浅部表现和成矿机制有重要意义.本文基于跨越申扎裂谷(青都段)的49个短周期地震仪记录的26个新型甲烷气爆震源和310个炸药震源信号,挑选了5378条P波初至和2379条S波初至震相到时.利用simul2000程序反演得到了申扎裂谷(青都段)浅层5 km内的高精度P波速度结构和P、S波速比.反演结果显示,P波速度结构与地形及地质构造具有高度的相关性,如裂谷内部低速特征指示了其内部松散填充物或破碎带的分布范围.在浅层,测线穿过的申扎裂谷(青都段)表现为一个超过20 km宽的半地堑模式,半地堑东边界为明显的断层陡坎,而西边界较为平坦.结合该区域发生的正断层地震事件及板片撕裂模型,本文提出了申扎裂谷可能的发育模式:首先,地壳底部岩浆的向上侵位导致了浅层局部变形,产生的拖曳作用形成拉张环境,在薄弱区裂开形成高角度正断层.然后,在底部岩浆的作用下韧性-脆性转换带抬升,整个断层系统通过滚动铰链机制旋转,更多的断层出现并伴随有地震活动,最终发育成裂谷系统.
During the rapid uplift of the Tibetan Plateau,a series of nearly north-south trending rift developed within the Gangdese orogenic belt due to the east-west extensional tectonic forces.The Xainza Rift and its surrounding region have been subjected to recurrent historical seismicity and encompass substantial mineral resources.Conducting a detailed investigation into the shallow subsurface fine structure of the Xainza Rift and its surrounding area is significant for gaining deeper insights into the internal morphology of the rift.This research is instrumental in enhancing our understanding of the shallow morphology and ore-forming mechanisms associated with the east-west extensional tectonic forces.Based on 49 short-period seismometers deployed around the Xainza Rift(Qingdu segment),we manually picked 5378 P-wave and 2379 S-wave first-arrival phases from 26-shots methane sources and 310 explosive sources in this study.By utilizing the simul2000 inversion program we obtained a high-precision P-wave velocity structure and P-wave,S-wave velocity ratio within the shallow 5 km of the Xainza Rift(Qingdu segment).The inversion results indicate a strong correlation between the P-wave velocity structure and topography as well as geological structures.For instance,the lowvelocity characteristics within rifts are indicative of the distribution range of loose infill or fault zones.In the shallow subsurface layer,the Xainza Rift(Qingdu segment)traversed by the seismic profile exhibits a halfgraben pattern with a width exceeding 20 km.The eastern boundary of the half-graben features a prominent fault scarp,whereas the western boundary appears relatively flat.Combining information such as the normal fault seismic events near the rift and slab tearing model,we have inferred a possible rift development model:Initially,the upward migration of magma at the base of the crust induced localized deformations in the shallow crust,creating a dragging effect that generated an extensional environment,where fractures developed in weak zones,forming high-angle normal faults.Subsequently,under the influence of the underlying magma,the ductile-tobrittle transition zone uplifted,and the entire fault system rotated through a rolling hinge mechanism,resulting in the emergence of additional faults accompanied by seismic activities,ultimately evolving into a rift system.
作者
冀战波
张云鹏
贺日政
李宗旭
JI ZhanBo;ZHANG YunPeng;HE RiZheng;LI ZongXu(Chinese Academy of Geological Sciences,Beijing 100037,China;Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Key Laboratory of Earthquake Source Physics,China Earthquake Administration,Beijing 100081,China)
出处
《地球物理学报》
北大核心
2025年第9期3386-3400,共15页
Chinese Journal of Geophysics
基金
西藏拉萨地球物理国家野外科学观测研究站开放课题(NORSLS20-05)
中国地质科学院基本科研业务费项目(JKY202214,JKY202015)
国家自然科学基金(42004079)
中国地质调查项目(DD20230008)联合资助.
关键词
申扎裂谷
甲烷震源
炸药震源
体波到时
速度结构
Xainza Rift
Methane source
Explosive source
Body wave arrival time
Velocity structure
