“从源到汇”研究2008年汶川地震对岷江流域地表过程的影响

地震制约着地貌演化和物质循环，极具特色的侵蚀、风化和沉积作用，其造成的物质输移通量成倍数增加，且可持续几年至几百年，但这类高强度事件对地球关键带过程的影响仍知之甚少，也是碳收支中最不确定组分之一。2008年汶川特大地震前后河流悬浮物和河水组成变化表明，地震对流域侵蚀、河水化学和碳输移有深远影响。然而，地震对这个地球关键带地表过程影响强度、幅度和趋势有待系统评估。本项目拟通过紫坪铺水库沉积序列粒度、磁学、有机、元素和多元同位素分析，开展地震前后流域侵蚀-风化强度对比研究；获得岷江悬浮物和河水化学组成与通量的季节/年际变化及其与径流量、震动强度和滑坡密度等关系；结合沉积速率、水文、滑坡等数据，“从源到汇”深入认识地震对流域侵蚀-风化过程的影响和机理。这一创新的研究思路和手段不仅有助于加深认识高强度构造事件的地表环境效应，而且对于阐明构造活跃带地球关键带侵蚀-风化以及碳循环机制具有深刻科学意义。

Earthquakes play a dominant role in the competition between topography build and surface processes that drive mountain belt evolution, with distinctive processes of erosion, weathering and sedimentation of some Earth’s critical zone. As a primary trigger of landslides, large earthquakes may cause many-fold increase in mass transfer and would last years to hundreds of years because of their dramatic perturbation to the natural system. However, poor understanding of the mechanism, rate and flux at which erosion and weathering generated by these kinds of events remains a key gap in our knowledge about long-term mountain denudation, sediment production, and carbon cycle. We started to monitor active sediment transport, river water chemistry, and particulate organic carbon (POC) in the Min Jiang following the 2008 Wenchuan earthquake since the end of 2009 and indicated that the earthquake has had significant effects on catchment erosion, river alkalinity flux, and POC export. A systematic evaluation is worth to further understanding the temporal and spatial impacts and trend of the earthquake on earth’s surface processes within the entire catchment. This project we propose to measure changes in grain size, magnetic and organic components, and concentrations of elements and isotopes of the pre- and post-event sediments from the Zipingpu reservoir that was built in 2005 just before the earthquake, in order to understand the difference between the pre- and post-event geophysical and geochemical inventories. Meanwhile we will monitor suspended particles and river water chemistry of main channel and major tributaries of the Min Jiang River to obtain seasonal and interannual variation in their chemistry and flux contribution and link them to water discharge, peak ground acceleration, and remote sensing inventories of total landslide volume. Being combined with chemistry and flux of pre-event suspended particle from Min Jiang stations, sedimentation rate, hydrological and landslide dataset, we expect to observe the difference in the river sediment after the earthquake, and if this is the case, these results will set the foundation for our deep understanding in catchment erosion and weathering processes associated with the tectonic event. Consequently, the specific focus of the proposed research will be to determine the effect of a large earthquake on (1) the sediment load, (2) the sediment geochemistry, (3) the catchment erosion and weathering processes, and (4) the organic carbon yield from a large river. The proposed work will fill a major gap by determining the magnitude of these effects associated with earthquake-triggered landslides, focusing on the case of the Wenchuan earthquake. The outcomes will form stand-alone outputs worthy of publication in high impact peer reviewed journals.