新疆塔什库尔干晚第四纪堰塞湖湖相沉积的古地震研究

Palaeoearthquake is of great scientific and realistic significance in the evaluation of earthquake hazard and fault activity. The dammed lacustrine sediments exposed at the tectonically active Tashkurgan area of the northeastern Pamir record various soft sediment structures such as diapir structure, ball and pillow structure, thixotropic mud dike and so on, which were possibly triggered by earthquake. In this study, we will conduct the detailed analysis of these soft sediment deformation structures on the type and feature, and further discuss the potential the mechanism of the formation. The shaking table model simulation will be demonstrated in order to establish the correlation of deformation structures with earthquake parameters. Meanwhile, the OSL and 14C chronology of lacustrine sediments will also be investigated for palaeoearthquake date, frequency and intensity during the late Quaternary. The study will provide crucial understanding for the linkage of Tashkurghan palaeaearthquake with the regional tectonic activities.

古地震研究对评估构造活跃地区地质灾害风险和断裂活动习性具有重要的理论和现实意义。塔什库尔干位于帕米尔高原东北部，晚第四纪构造活动强烈，导致该地区堰塞湖湖相沉积广布。这些湖相沉积物中常见发育多种可能与地震活动有关的软沉积物变形构造，如底辟构造、球枕构造、触变泥脉等。本项目拟对这些软沉积物变形构造开展细致研究，查明主要变形构造类型和特征，探讨其成因。在此基础上，采用振动台开展室内模拟试验，模拟软沉积物变形过程，尝试建立这些变形构造类型、强度与地震动参数之间的相关关系。与此同时，结合光释光和14C测年，探讨该地区地震活动时间、频次和强度及其与区域构造活动之间的可能联系。

古地震研究对地质灾害风险评估和断裂活动性评价具有重要的科学意义。地震成因的软沉积变形构造可指示区域断裂活动信息，而构造活动活跃地区的古堰塞湖湖相沉积是记录软沉积变形构造的最佳载体。本文选择帕米尔东北部塔什库尔干晚第四纪古堰塞湖湖相沉积，开展详细的软沉积变形构造研究，在该区湖相沉积地层中识别出与地震成因有关的多种软沉积变形构造，主要包括与重力作用相关的软沉积变形构造（负载构造、滑动构造），与砂层液化作用相关的软沉积变形构造（砂岩脉、液化滴状体、底劈与枕状构造），复合变形构造（触变泥岩柱、触变板块体、砂层液化-泥岩触变-滑动构造）。根据区域构造背景和振动台模拟实验结果表明，该地区记录的软沉积变形构造是由M>6级强地震引起，发震断裂可能为公格尔拉张系南部断裂。AMS 14C年代结果表明，软沉积物变形构造形成于25790±90 yr BP 和21270±80 yr BP之间，指示晚更新世时期该地区较强的断裂活动。本项研究不仅为中国西部地区构造活动与区域地球动力学提供具有基础依据，而且为塔什库尔干河下游下板地水库大坝的防震建设提供必要的地质背景。