Long runout geological disaster initiated by the ridge-top rockslide in a strong earthquake area: A case study of the Xinmo landslide in Maoxian County, Sichuan Province
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摘要:
近年来，在汶川地震等强震区常发生一种特大的高位滑坡地质灾害，它从高陡斜坡上部位置剪出并形成凌空加速坠落，具有撞击粉碎效应和动力侵蚀效应，导致滑体解体碎化，从而转化为高速远程碎屑流滑动或泥石流流动，并铲刮下部岩土体，使体积明显增加。新磨滑坡就是这种典型，它发生于2017年6月24日，滑坡后缘高程约3450m，前缘高程约2250 m，高差1200 m，水平距离2800 m，堆积体体积达1637×104 m3，摧毁了新磨村村庄，导致83人死亡。新磨滑坡地处叠溪较场弧形构造带前弧西翼，母岩为中三叠统中厚层变砂岩夹板岩，是1933年叠溪Ms7.5级震中区（烈度X度）和汶川Ms8.0级强震区（烈度IX度），形成震裂山体。滑源区分布多组不连续结构面，将厚层块状岩体分割成碎裂块体，在高程3150~3450 m区间形成明显的压裂鼓胀区，特别是存在2组反倾节理带，具有典型的“锁固段”失稳机理。滑坡体高位剪出滑动，连续加载并堆积于斜坡体上部，体积达390×104 m3，导致残坡积岩土层失稳并转化为管道型碎屑流；碎屑流高速流滑至斜坡下部老滑坡堆积体后，因前方地形开阔、坡度变缓，转化为扩散型碎屑流散落堆积，具有“高速远程”成灾模式。据此，可建立强震山区高位滑坡的早期识别方法，当陡倾山脊存在大型岩质高位滑坡时，应当考虑冲击作用带来的动力侵蚀效应和堆积加载效应，特别是沿沟谷赋存丰富的地下水时，发生高速远程滑坡的可能性将明显增加。因此，在地质灾害调查排查中，在高位岩质滑坡剪出口下方的斜坡堆积体上的聚居区等应划定为地质灾害危险区。在强震山区地质灾害研究中，不仅应采用静力学理论分析滑坡的失稳机理，而且应采用动力学方法加强运动过程的成灾模式研究。
Abstract:In recent years, a typical type of catastrophic ridge-top (or high-position) rockslide often occur in the strong earthquakes such as the Wenchuan earthquake. It exits out from the upper part of the steep slope and forms a volley fall with impact and crushing effect and dynamic erosion effect, causing the slide body to disintegrate and fragment, which transforms into rapid and long run-out avalanche debris or debris flow, and entraining the lower part of rock and soil mass, so that the volume increased significantly. The Xinmo landslide is this typical, it occurred at Maoxian County, Sichuan Province on June 24, 2017. The elevation of the crown of the Xinmo landslide was about 3450 m and the front edge was about 2250m. The height difference of landslide was 1200m, and the horizontal distance was about 2800 m. Its volume was up to 16.37 million m3. The landslide buried the Xinmo Village, leading to the death of 83 people. The Xinmo landslide was located on the western wing of the Jiaochang arc-shaped tectonics. Its parent rocks were the medium to thick layered metamorphic sandstone intercalated with slate in the Middle Triassic. The region was not only the epicenter area of the Diexi earthquake with magnitude 7.5 in 1933 (the intensity of the earthquake was X) but also the strong earthquake-affected area of the Wenchuan Ms8.0 earthquake in 2008 (the intensity was IX). The mountains, especially the ridge-top rockmass, were fractured/cracked due to the strong earthquakes. There were multiple groups of discontinuous structural planes in the sliding source zone, and hence the thick blocky rock mass was cracked into fragmented blocks, and the bugling area was formed at the elevation varying from 3150 to 3450 meter. In particular, there were two sets of anti-dip large joints in the sliding source area, indicating a typical failure mechanism "locked-section". Rockslide with a volume of 3.9 million m3 exited and continuously accumulated at the back of previous residual landslide. The "overload effect" triggered the slope instability under the exit and transferred into long runout channeled avalanche debris. Because the terrain was wide and the slope angle gradually decreased, avalanche debris converted to diffused one and then to scattered accumulation. The Xinmo landslide presents a typical disaster mode of the rapid and long runout initialed due to rockslide at ridge-top in strong earthquake area. A new method should be established to recognize this type of landslides. Wherever there are large-scale rockslides in steep ridge-top region, the "dynamic erosion effect" and the "overloading effect" on the previous accumulation and the talus of slope due to impact processes should be considered. Especially in the place where there is abundant groundwater along the gully, the possibility of a rapid and long runout rockslide-avalanche debris will increase. Therefore, in conducting the investigation of geological disaster, the town, village or other populated areas should be zoned as risk area on the previous landslide accumulation of slope below the exit of the rockslide at the ridge-top. The authors emphasize that, in the strong earthquake mountainous regions, the static balance method for the landslide stability should be considered, and the dynamic research on the landslide runout processes and the disaster mode should be strengthened.
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Keywords:
- ridge-top landslide /
- avalanche debris /
- strong earthquake area /
- Maoxian County
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深部地质调查工程（首席专家吕庆田研究员）隶属中国地质调查局十大计划之一的“基础地质调查计划”。该工程由4个项目组成，分别是“松辽盆地资源与环境深部钻探工程（王稳石），松辽盆地深部油气基础地质调查（侯贺晟），钦杭结合带及邻区深部地质调查（严加永）和祁连－天山及周缘盆山结合带深部地质调查（陈宣华）”。
工程选择我国资源、能源重要基地、重大地质边界和构造单元，通过综合地球物理探测和科学钻探等手段，揭示成矿成藏系统深部过程、结构和形成规律，阐明中生代环境气候演变规律、控制要素，揭示关键造山带及盆山深部精细结构，抢占大陆基础地质研究的国际制高点，引领国际深部地质研究前沿，推动地质调查向深部进军。经过3年的努力，工程在深层油气发现、超深钻探技术、重大基础地质问题等方面取得重大进展。
1.“松科二井”科学钻探工程打破多项世界纪录，取得系列技术创新。“松科二井”完钻深度7018 m，成为国际大陆科学钻探组织（ICDP）成立以来实施的最深科学钻探工程，亚洲国家实施的最深大陆科学钻探井，是国际上连续取心最深、长度最大的钻探工程（2863.23~7018m），岩心采取率高达96.6%。创造了311 mm口径深部地层连续取心1650.51 m，311 mm口径同径取心钻进单回次取心长度超30 m，216 mm口径在井深超4700 m井段单回次取心长度超40 m，152 mm口径在井深超6900 m井段单回次取心长度超30 m四项世界纪录；攻克了深部高温钻井系列技术难题；开发出311 mm和216 mm大口径中空井底动力绳索取心钻具，实现绳索取心和提钻取心两种技术快速切换；研发出152 mm地表驱动绳索取心钻具，在6400m以深钻井中成功应用。
2.“松科二井”科学钻探工程及松科盆地深部地质调查取得系列重大科学发现。获取了“松科二井”沙河子组十大地质记录，发现沙河子组年代为112~121 Ma，物源区主要来自大兴安岭地区。发现沙河子组四段底部主要受岁差和偏心率控制的东南季风的影响，发育优质的烃源岩，为进一步分析松辽深层油气成因的物质基础提供了依据。发现松辽盆地基底存在三叠纪火山—沉积地层，为研究松辽盆地的形成与演化提供了新的重要线索。通过对“松科二井”岩性、烃源岩、气测异常、罐顶气和孔隙度等参数分析研究，获得了470~7018 m井段垂向油气特征，并划分为6个明显区段，完整揭示了白垩系和前侏罗系的轻烃分布特征，为今后评价和勘探松辽盆地深部油气资源提供了依据。深地震反射剖面发现疑似上古生界的地震反射信息，为进一步探索松辽盆地形成机理和深层油气赋存基础提供了重要信息。
3.华南东南部综合地球物理探测深化了区域构造格架、地壳结构和演化的认识，取得了系列新发现。接收函数和重力反演揭示华南东南部的Moho面起伏整体较为平缓，自东向西逐渐增厚；长江下游、钦杭东段、武夷山和东南沿海地壳泊松比普遍较高，指示幔源物质注入地壳增多，壳幔作用强烈，而南岭和江南造山带西段地壳平均泊松比较低，指示地壳偏酸性，壳幔作用较弱；华南东南部岩石圈电性结构结果发现长江中下游、钦杭等重要成矿带对应地壳和岩石圈的低阻通道，认为它不仅代表了块体边界，还是中生代深部岩浆/流体迁移的“通道”，对区域成矿具有重要的控制作用。深地震反射剖面发现江南造山带保留清晰的“碰撞造山带”结构，即下地壳连续多处出现“楔状”构造和地壳“鳄鱼”构造，提出了中生代在古太平洋板块远程挤压应力作用下，造山带“活化”控制了中生代陆内成矿系统的形成和演化的新认识。
4.复杂造山带及盆山结构研究取得重要进展。祁连-天山及周缘盆山结合带深部地质调查取得重要地质新认识：揭示出柴达木地块北缘、祁连山造山带和阿拉善地块的全地壳结构及复杂深部关系，提出了早古生代北祁连洋双向俯冲、北祁连造山带和阿拉善地块深部逆冲叠瓦与双重构造、祁连山北缘榆木山逆冲推覆和飞来峰构造以及早白垩世陆内伸展等新认识；建立了祁连造山带新元古代以来的构造演化模式。厘定了塔里木盆地北缘库车凹陷的沉积厚度，揭示出准噶尔盆地南缘沉积岩最大厚度可达13000 m；发现南天山南缘长距离逆冲推覆构造（达60 km），天山北缘山前带逆掩推覆构造（推覆距离达20 km）；厘定了天山造山带与塔里木盆地结合带中生代以来晚三叠世、古近纪、新近纪和第四纪共4期构造变形序列与生长地层记录，明确了西天山造山带与塔里木盆地、准噶尔盆地之间的盆山耦合关系，再现了新生代以来印度－亚洲大陆碰撞对欧亚大陆改造的效应。
项目自实施以来，不仅在深部基础地质、探测技术创新等方面取得重大进展，还在人才培养上成绩显著。先后1人获得国家“万人计划”领军人才，1人入选国土资源部领军人才，1人获地质调查局卓越地质人才，2人获地质调查局优秀地质人才。2个团队入选自然资源部（国土资源部）科技创新团队。先后培养博士、硕士30余名，参与组织2次国际会议，参加国内外重要学术会议近50余人次。获得3项“十三五”国家重点研发计划项目，先后发表论文100余篇，专著2部，解决了一批重大基础地质问题，形成了一支具有国际水平的深部探测研究团队。
致谢: 张勤教授和赵超英教授提供了InSAR解译成果，赵永教授提供了滑坡地震记录成果，审稿专家和编辑老师对文章提出了宝贵的意见和建议，在此一并表示衷心感谢！ -
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图 2 茂县新磨滑坡特征分区及多期遥感影像对比
Figure 2. Characteristic zoning and comparison of the multi-temporal remote sensing images of the Xinmo landslide
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图 3 茂县新磨滑坡及周边地质特征
Figure 3. Geological formations in and around the Xinmo landslide at Maoxian County
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图 4 茂县新磨滑坡区域地震烈度图（1933年叠溪Ms7.5级地震和2008年汶川Ms8.0级地震）
Figure 4. Regional seismic intensity map of the Xinmo landslide (Intensity contour of the Diexi Ms7.5 earthquake in 1933 and the Wenchuan Ms8.0 earthquake in 2008)
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图 5 1933年叠溪Ms7.5级地震震中区大型滑坡及堰塞湖分布图
Figure 5. Distribution of large-scale landslides and barrier lakes in epicentral area of Diexi Ms7.5 earthquake
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图 6 茂县新磨滑坡附近降雨曲线
Figure 6. Curve of rainfall process around Xinmo Village from May 1 to June 23 of 2017
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图 7 茂县新磨滑坡滑动前遥感影像及典型照片
Figure 7. Remote sensing image and typical photos of the Xinmo landslide 37 hours before sliding
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图 8 茂县新磨滑坡滑动前和滑动后工程地质剖面图
Figure 8. Engineering geological section of the Xinmo landslide before and after sliding
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图 9 茂县新磨滑坡滑源区岩体结构特征
Figure 9. Rockmass structure characteristics of the sliding source zone of the Xinmo landslide at the ridge-top
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图 10 茂县新磨滑坡-碎屑流堆积特征
Figure 10. Accumulation characteristics of rockslide-avalanche debris at Xinmo village, Maoxian County, Sichuan
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图 11 茂县新磨滑坡滑前InSAR解译结果
Figure 11. The InSAR interpretation of the Xinmo landslide before sliding
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图 12 茂县新磨滑坡发生前37小时滑源区鼓胀裂缝照片
Figure 12. Photo showing the bulging cracks of the sliding source zone which were taken 37 hours before the Xinmo landslide
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图 13 茂县新磨滑坡运动速度几何剖面及计算结果
Figure 13. Geometric section and calculation curve of the runout velocity of the Xinmo landslide
表 1 茂县新磨滑坡物源和堆积分区
Table 1 Zoning of material sources and accumulation of the Xinmo landslide, Maoxian County
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