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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Protracted river response to medieval earthquakes
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Protracted river response to medieval earthquakes

机译：长期的河流反应中世纪地震

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Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from seismic disturbances, depending on how recovery is defined. We examine three principal proxies of river recovery after earthquake-induced sediment pulses around Pokhara, Nepal's second largest city. Freshly exhumed cohorts of floodplain trees in growth position indicate rapid and pulsed sedimentation that formed a fan covering 150 km(2) in a Lesser Himalayan basin with tens of metres of debris between the 11th and 15th centuries AD. Radiocarbon dates of buried trees are consistent with those of nearby valley deposits linked to major medieval earthquakes, such that we can estimate average rates of re-incision since. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos, and dated tree trunks to reconstruct geomorphic marker surfaces. The volumes of sediment relative to these surfaces require average net sediment yields of up to 4200 t km(-2) yr(-1) for the 650 years since the last inferred earthquake-triggered sediment pulse. The lithological composition of channel bedload differs from that of local bedrock, confirming that rivers are still mostly evacuating medieval valley fills, locally incising at rates of up to 0.2 m yr(-1). Pronounced knickpoints and epigenetic gorges at tributary junctions further illustrate the protracted fluvial response; only the distal portions of the earthquake-derived sediment wedges have been cut to near their base. Our results challenge the notion that mountain rivers recover speedily from earthquakes within years to decades. The valley fills around Pokhara show that even highly erosive Himalayan rivers may need more than several centuries to adjust to catastrophic perturbations. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning i
机译：山区通过迅速加剧来应对强烈的地震以容纳通过共同地震山体滑坡提供的多余沉积物。详细的沉积预算表明，河流需要几年时间才能从地震干扰中恢复，具体取决于定义恢复。在尼泊尔第二大城市的Pokhara周围地震诱导的沉积物脉冲后，研究了三个河流恢复的主要代理。在成长的洪泛区的洪泛区的新膨胀的队列表明了快速和脉冲沉降，形成了一个覆盖了150公里（2）的风扇，在较小的喜马拉雅盆地，在11日和15世纪广告之间。埋地树的Radiocarbon日期与与主要中世纪地震相关的附近的山谷矿床符合，这样我们就可以估计自从。我们将高分辨率数字高度数据，大地测量场调查，天线照片和日期树干组合在一起重建地貌标记表面。由于最后推断地震触发沉积物脉冲，相对于这些表面相对于这些表面的沉积物的量需要平均净沉积物，其净沉积物高达4200吨（-2）YR（-1）。通道床单的岩性组成与当地基岩的岩性组成不同，确认河流仍然大多数疏散中世纪谷填充，在速率下达到最高0.2米的速率（-1）。在支路交界处的明显的基点和表观遗传峡谷进一步说明了延长的河流反应;只有地震衍生的沉积物楔的远端部分被切割到其底部附近。我们的成果挑战山区在几年内从地震迅速恢复的概念。山谷填补了Pokhara表明，即使是高度腐蚀的喜马拉雅河也可能需要超过几个世纪以来调整到灾难性的扰动。我们的结果激发了一些重新思考后地震危害评估和基础设施规划我

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