Preliminary Study on the Characteristics of Landslides and Soil Liquefaction Triggered by the Dingri MS6.8 Earthquake on January 7, 2025, Southern Tibetan Plateau
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摘要:
现今强震触发次生灾害空间展布的快速遥感制图,对强震致灾机理完整认识有重要意义,青藏高原具有高海拔、人口稀少、野外调查困难等特点,因此,利用震后高分辨率卫星影像开展地震触发滑坡及砂土液化的分布规律研究,具有特别重要的研究意义.为了系统获取2025年1月7日定日MS6.8地震触发的次生灾害的空间展布特征,利用国产卫星的应急成像影像数据,通过震前、震后影像对比的人工目视解译方法,结合野外实地调查,获得如下认识:(1)定日地震触发的同震滑坡2 869处,具有南北两个集中分布区,60%集中海拔为5 000~6 000 m的区域,且以坡面碎屑及局部崩塌为主,土方量较小,远离居民点;(2)定日地震触发的砂土液化点~40万处,集中分布在海拔为4 100~4 300 m的朋曲河的河漫滩及低阶地上,德么错盆地、郭加盆地、定结盆地均有密集分布,部分位于5 200 m的第四纪冰碛物中.此次定日地震触发的同震滑坡以位于高海拔区域(~5 000 m)的有限的坡面碎屑流为主,可能对应高海拔区域的基岩表层风化层的陡坡度部位的震中地形放大效应,而砂土液化空间分布覆盖定结‒申扎裂谷南段的3个盆地,表明裂谷系的次级断裂的破裂事件可以导致邻近多个盆地内的严重同震液化现象,与各自盆地断裂是否发生破裂无关.
Abstract:The rapid mapping of secondary effects triggered by strong earthquakes is crucial for understanding the disaster-causing mechanisms of mainshock events. The Tibetan Plateau, characterized by its higher altitude, sparse population, and challenging field conditions, presents significant difficulties for on-site investigations. Consequently, it is significant to analyze the distribution of earthquake-induced landslides and soil liquefaction utilizing post-earthquake emergency satellite imagery. We aim to systematically identify the spatial distribution characteristics of secondary hazards triggered by the MS6.8 Dingri earthquake on January 7, 2025. We utilized emergency imaging data from high-resolution Chinese satellite images. We employed manual visual interpretation through a comparative analysis of pre- and post-earthquake imagery supplemented by field investigations. The following results are obtained: (1) The mainshock triggered 2 869 coseismic landslides, with two major concentration zones in the north and south. Approximately 60% of these landslides occurred in high-altitude regions between 5 000-6 000 m, predominantly manifesting as slope debris flows and collapses with limited effect for far away the residents. (2) The mainshock also induced about 400, 000 soil liquefaction pits, primarily concentrated in the floodplains and low terraces of the Pengqu River at elevations of 4 100-4 300 m. These liquefaction sites are distributed across the Democuo Basin, Guojia Basin, and Dingjie Basin, with some occurrences in Quaternary tills at elevations reaching 5 200 m. The distribution pattern of coseismic landslides, primarily as slope debris flows in higher-altitude (about 5 000 m) areas, suggests a possible correlation with the topographic amplification effect. Meanwhile, the spatial extent of soil liquefaction, spanning three basins in the southern section of the Dingjie-Shenzha Rift system, indicates that single secondary-fault rupture event within a single basin can significantly impact other adjacent secondary-faulted basins, leading to severe secondary disasters, even the controlled faults without coseismal faulting.
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图 1 藏南裂谷系区域构造
藏南裂谷系名称(自东向西):①错那‒桑日裂谷系(COR);②亚东‒谷露裂谷系(YGR);③定结‒申扎裂谷系(DXR);④岗嘎‒当惹雍措裂谷系(GTR);⑤聂拉木‒措勤裂谷系(NCR);⑥仲巴‒塔若错裂谷系(ZTR);⑦江曲藏布‒改泽裂谷系(JGR);⑧普兰‒文布当桑裂谷系(BWR);断裂名称:MFT.主前锋逆冲断裂带;NGT.娜迦逆冲带;SGF.实皆断裂带;JLF.嘉黎断裂带;KKF.喀拉‒昆仑断裂带;GDF.改则‒洞错断裂带;LBF.龙木错‒独立石湖断裂;DNF.多玛‒尼玛断裂带;GCF.格仁错断裂带;BCF.崩错断裂带;EKF.东昆仑断裂带;GZ-YSF.甘孜‒玉树断裂带
Fig. 1. Tectonic map of the southern Tibetan rift systems
图 3 定日地震震中区及周边的震前(黑色多边形)、震后(红色多边形)卫星影像覆盖分布
震前影像获取时间为震前1个月内,可以准确代表震前震中区的地表地貌特征;震后影像获取时间为地震当天至5 d内,覆盖的范围包含了Ⅶ度区的绝大部分区域,Ⅶ度区北侧拉孜县附近的区域未覆盖
Fig. 3. Satellite image coverage distribution map of the epicenter of the Dingri earthquake and its surrounding areas before the earthquake (black polygons) and after the mainshock (red polygons)
图 4 地震当天3 h后获取的GF-1C卫星影像(a)显示拉昂村东北方向发育在冰碛物上的同震地表破裂及触发的5 200 m以上的同震滑坡(b)(位置见图 3)
同震地表破裂沿德么错断裂已有迹线展布(a),同震地表变形带局部宽度可达300 m;第四纪冰碛物上发育有砂土液化和震动变形带;同震滑坡主要沿着朋曲河与雅鲁藏布江的分水岭一带发育,解译的同震滑坡(粉红色多边形)以沿坡面的崩塌或坡面碎屑流为主(b),坡脚堆积规模有限表明滑坡的实际体积远小于预期
Fig. 4. The fresh GF-1C image (a) acquired 3 h after the mainshock showing the coseismic surface rupture developed on the moraine and the coseismic landslides (b) with an altitude of about 5 200 m at northeast of La'ang Village (see the location in Fig. 3)
图 5 定日地震震中措果乡附近的朋曲河河谷震前(a)、震后(b‒d)卫星影像上同震密集砂土液化导致的河漫滩及低阶地上的纹理显著差异,茶布南(e)、朋曲河与叶如茶布河交汇处(f)及定结县东北侧的叶如藏布河谷(g)的密集砂土液化(位置见图 11)
Fig. 5. Satellite images of the Pengqu River valley near the epicenter, Cuoguo Township, before (a) and after (b‒d) the earthquake show significant differences in texture on the river floodplain and low terraces caused by densely coseismic soil liquefaction. Dense soil liquefaction at site of southern of Chabu Village (e), the site of confluence of the Pengqu River and the Yeruchabu River (f) and valley of Yeruzangbo River Valley, northeast of Dingjie County (g) (see the location in Fig. 11)
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