| 汶川地震同震滑坡物质在震区的滞留和运移及其对龙门山地形演化的影响 |
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| 引用本文： | 王伟,刘静,Vincent Godard,张金玉,许冲,李志刚,徐心悦,许强,王鹏,谢克家.汶川地震同震滑坡物质在震区的滞留和运移及其对龙门山地形演化的影响[J].地球物理学报,2018,61(5):1970-1983. |
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| 作者姓名： | 王伟 刘静 Vincent Godard 张金玉 许冲 李志刚 徐心悦 许强 王鹏 谢克家 |
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| 作者单位： | 1. 中国地震局地质研究所, 地震动力学国家重点实验室, 北京 100029;2. Aix-Marseille Université, CNRS, IRD, Collège de France, CEREGE, Aix en Provence 13100, France;3. 中国地震局地质研究所, 活动构造与火山重点实验室, 北京 100029;4. 中山大学地球科学与工程学院, 广东省地球动力作用与地质灾害重点实验室, 广州 510275;5. 中国科学院青藏高原研究所, 北京 100101;6. 河南省有色金属矿产探测工程技术研究中心, 郑州 450016 |
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| 基金项目： | 国家自然科学基金项目（41172179，41225010和41761144065），中国地震局地质研究所地震动力学国家重点实验室自主项目（LED2016A02）和国家重点研发计划项目（2016YFC0600310）共同资助. |
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| 摘 要： | 2008年MW7.9汶川地震导致龙门山断裂发生强烈地壳变形，同时引发的巨量同震滑坡加速了该地区的地表剥蚀和河流侵蚀.然而，目前尚缺少系统的数据定量研究滑坡物质的运移以及河流侵蚀速率随时间的演化规律，这些对理解龙门山前缘物质的再分配以及强震对活动造山带地形塑造的作用至关重要.为此，本研究在汶川地震后的6年间，对震区沱江上游3条支流湔江、石亭江、绵远河流域进行了多期次的定点现代河沙采样.通过系统测量河沙中的石英10Be浓度，并与震前已发表的数据进行对比，发现如下基本特点：（1）震后河沙10Be浓度均有明显降低，表明同震滑坡物质对河沙的稀释作用；（2）震后河流对河沙的运移量增加为震前的1.3~18.5倍，因此震后龙门山地区侵蚀速率短期显著增加；（3）初步估计得到汶川地震产生的滑坡物质被完全运移出造山带所需要的时间至少为100~4000年，接近龙门山地区强震复发周期；（4）震间和同震产生的构造变形和地表剥蚀在空间上具有互补性.考虑到地表剥蚀引起的地壳均衡反弹效应，认为类似汶川地震的强震有利于龙门山的隆升.认识震前、震时和震后的地壳变形及侵蚀过程有助于更好地理解单次强震事件对高原边界龙门山地形演化的作用.
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| 关 键 词： | 龙门山 汶川地震 同震滑坡 河流卸载 地形演化 |
| 收稿时间： | 2018-02-06 |
Retention and transport of coseismic landslide sediments induced by the Wenchuan earthquake,and its implication for the topographic evolution of the Longmen Shan |
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| WANG Wei,LIU Jing,Vincent Godard,ZHANG JinYu,XU Chong,LI ZhiGang,XU XinYue,XU Qiang,WANG Peng,XIE KeJia.Retention and transport of coseismic landslide sediments induced by the Wenchuan earthquake,and its implication for the topographic evolution of the Longmen Shan[J].Chinese Journal of Geophysics,2018,61(5):1970-1983. |
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| Authors: | WANG Wei LIU Jing Vincent Godard ZHANG JinYu XU Chong LI ZhiGang XU XinYue XU Qiang WANG Peng XIE KeJia |
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| Abstract: | The 2008 MW7.9 Wenchuan earthquake, China, ruptured the parallel Beichuan and Pengguan faults along the Longmen Shan, eastern margin of the Tibetan plateau, which induced a large amount of landslides, volume comparable to the coseismic uplift. However, there lacks systematic data and research to quantify the removal of these loose materials and temporal variation of fluvial erosion rates, which is central to understand the mass redistribution along the Longmen Shan and the role of such earthquake in building topography in active mountain ranges. Over the period of 2008—2013 after the Wenchuan earthquake, we collected a series of river sand samples along three tributaries of the Tuojiang River, including the Jianjiang, Shiting Jiang, and Mianyuan River, and measured the detrital quartz 10Be concentration. Together with published river sand 10Be concentration prior to the Wenchuan earthquake, our results show that:(1) Detrital 10Be concentration declined dramatically after the Wenchuan earthquake, which shows the dilution effect of co-seismic landslides; (2) Fluvial erosion rate in the upstream of Mianyuan River increased to 1.3~18.5 times of the pre-earthquake level, which indicates there occurs an obvious increase of erosion rates shortly after the earthquake; (3) Under the assumption of constant erosion rate, a simple calculation indicates the river will take at least 100~4000 years to move away these loose materials, comparable to the return time of Wenchuan-type large-magnitude earthquake in the Longmen Shan. Considering the effect of isostasy, we think that the Wenchuan earthquake will lead to a net material surplus in the Longmen Shan; and (4) The vertical motion and denudation at surface during the interseismic period and cosesimic rupture have different spatial pattern, which together control the topographic evolution of eastern Tibet. |
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| Keywords: | Longmen Shan Wenchuan earthquake Co-seismic landslides Fluvial processes Topographic evolution |
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