晚第四纪以来罗云山山前冲沟裂点时空序列及其与断裂活动的关系

Using various technical means available to restore the history of the fault tectonic activity since late Quaternary completely and reliably is the premise and foundation to establish the model of the fault activity, assess seismogenic capacity and predict the future behavior of the fault. The latest research results show that the integrity of the paleoearthquake sequence revealed by traditional trenching method needs further examination, supplement and completion due to limited by the location, depth and scale of the trench excavation. In order to establish temporal and spatial sequence of knickpoints of gullies along the Luoyunshan Mts. Piedmont, this project intends to measure long-profiles of the gullies across the Luoyunshan Mts. Piedmont Fault in the field by the differential GPS technology and sampling and dating sediments well preserved in the typical terraces, and exclude the non-tectonic knickpoints by regional comparison. Analyzing the relationship between tectonic knickpoints and the number, time and vertical dislocation component of the fault activity. The paleoearthquake sequence since late Quaternary obtained by the knickpoint sequence will be compared with previous study on the paleoearthquake of the fault revealed by trenches. Both the similarities and differences and possible reasons will be analyzed to establish more complete paleoearthquake sequence supported each other by geomorphologic and sedimentary evidence. This project aims to complement and improve the traditional trenching method, provide theoretical and methodological support for the research of active tectonics and basic data for regional earthquake disaster defense.

利用各种可能的技术手段完整可靠地恢复断层晚第四纪以来的构造活动历史是建立断层活动模型、评估断层发震能力和预测断层未来行为的前提和基础。最新研究结果表明，传统探槽方法所揭示古地震序列因受位置、深度和规模所限，其完整性需要进一步检验、补充和完善。本项目拟利用差分GPS技术和测年技术，野外实地测量横穿罗云山山前断裂的冲沟纵剖面，并对沉积物保存较好的典型阶地取样测年，建立罗云山山前冲沟裂点的时空序列，通过区域对比剔除非构造裂点，分析构造裂点与断裂活动期次、时代和垂向断错分量之间可能存在的关系，提取裂点序列所记录的罗云山山前断裂晚第四纪以来的古地震活动信息。在此基础上与前人对该断裂开展的探槽古地震研究进行对比，分析二者异同及可能原因，建立地貌与沉积证据相互支撑的较完整的古地震序列。项目旨在，对传统的古地震探槽方法作补充完善，为活动构造研究提供理论和方法上的支持，并为区域震害防御提供基础资料。

本项目利用差分GPS野外实地测量了28条横穿罗云山山前断裂的冲沟纵剖面，并对沉积物保存较好的典型阶地取样测年，获得了罗云山山前冲沟裂点的时空序列，通过6级裂点序列获得了罗云山山前断裂距今约2.8万年以来6次古地震事件，复发间隔接近，具有准周期复发特征。在此基础上与之前对该断裂开展的探槽古地震研究进行对比发现，通过冲沟裂点调查与探槽开挖揭示的断裂古地震事件在发生时间段上较为吻合，且古地震事件垂直位移基本一致，说明本项目通过裂点序列研究断裂古地震序列是可行的。最后，通过比较分析建立了地貌与沉积证据相互支撑的较完整的古地震序列。也即，距今约2.8万年以来罗云山山前断裂发生了6次古地震事件，并具有准周期复发特征，复发间隔为4585a。古地震事件垂直位移为2.4-3.0m，对应的古地震震级为7.0~7.5级。本项目旨在，对传统的古地震探槽方法作补充完善，为活动构造研究提供理论和方法上的支持，并为区域震害防御提供基础资料。