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藏南丁木错地堑断陷盆地的构造特征与活动历史及其对定日MS6.8级地震强变形带的启示

Tectonic characteristics and activity history of the Dingmu Co fault-bounded basin in southern Xizang and its implications for the earthquake deformation zone of the MS6.8 Dingri earthquake

  • 摘要: 自定日县“1.07”地震发生以来,学者们针对震后灾害、震源机制、发震构造等开展了大量研究,但对丁木错断陷盆地内的沉积、构造等基础地质背景缺乏系统的认识,严重制约了发震机制的研究。本文以2022−2024年在该区域开展的1︰5万区域地质调查为基础,详细阐述了丁木错断陷盆地及其所在区域的沉积物特征、构造特征以及震前采集的音频大地电磁和土壤氡气测量成果,并对控制丁木错断陷盆地的边界断裂破碎带开展了OSL测年工作。结果显示,丁木错断陷盆地湖积物中发育大量地震成因的软沉积物变形,表明该区域古地震活动强烈。丁木错断陷盆地北部发育东西向展布的箕状构造,东部发育大量南北向走滑正断层。音频大地电磁测量揭示盆地内发育超过七条隐伏断层,土壤氡气测量结果表明盆地东部断层活动性强于中部。丁木错断陷盆地是由南北向走滑正断层系和东西向拉轨岗日伸展拆离系共同作用的产物,自晚更新世以来,至少经历了~53.4 ka BP、~37.1~32.2 ka BP、~9.2ka BP三个历史强活动期,且目前正处于一个新的强活动期。定日1.07地震引发的强变形带多分布于南北向与东西向、北东向、北西向断层的交汇区域,因此在未来的地质监测与灾害风险评估工作中,应将此类断层构造的交汇部位作为重点关注对象。

     

    Abstract: The MW7.1 earthquake that struck Dingri County on January 7, 2025, has prompted extensive investigations into its post-seismic hazards, focal mechanism, and seismogenic structure. However, the absence of a systematic understanding the sedimentary framework, structural architecture, and other key geological characteristics of the Dingmu Co fault-bounded basin has hindered such efforts. Drawing on a 1:50,000-scale regional geological survey, we examined the sedimentary and structural features of the basin. We further integrated pre-earthquake audio-frequency magnetotelluric (AMT) and soil-radon survey data with optically stimulated luminescence dating of the fault fracture zones. Our results reveal that lacustrine deposits in the basin host abundant seismically induced soft-sediment deformation structures. The northern sector contains an east-west-trending half-graben, and the eastern sector is dominated by several north-south-trending strike-slip normal faults. AMT data have identified multiple concealed faults, and soil-radon measurements indicate heightened fault activity east of the central basin area. Shaped by the combined influence of the north-south-trending Dingmu Co strike-slip-normal fault system and east-west-trending Lhagoi Kangri Detachment System, the basin has undergone at least three episodes of intense tectonic activity since the Late Pleistocene, at ~53.4, ~37.1–32.2, and ~9.2 ka BP, and is presently experiencing renewed deformation. Coseismic deformation associated with the January 7 event was concentrated at the intersections of north-south-, east-west-, northeast-, and northwest-trending faults. These results indicate the need to prioritize such intersection zones in future geological monitoring and disaster risk assessments. Overall, this study offers new insights for advancing seismotectonic research and understanding earthquake hazards in the Himalayan orogenic belt.

     

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