2022年MS6.8泸定地震诱发滑坡中过剩地形的影响

doi:10.3969/j.issn.0253-4967.2024.04.002

摘要/Abstract

摘要：

地貌演化受到构造活动和河流侵蚀等作用影响。作为地貌演化的重要组成部分, 滑坡对于塑造地貌形态起到了重要作用。滑坡发生的本质是坡体平衡受到破坏, 而这种不平衡现象可体现为存在过剩地形。2022年9月5日四川省泸定县 M_S6.8 地震诱发了大量山体滑坡, 为研究过剩地形对同震滑坡的空间分布提供了一个研究实例。文中基于震后遥感影像对同震滑坡进行了提取, 并依据ALOS 12.5m地形高程数据计算了震区过剩地形。此次工作共识别出1 485个滑坡(面积约为14.83km²), 这些同震滑坡多为浅层滑坡, 呈带状集中分布于大渡河两侧。同时, 过剩地形的计算结果显示其主要分布在大渡河及其支流的山谷两侧。相关性分析结果表明, 高达91.7%的同震滑坡分布在不同厚度的过剩地形分布区。为了进一步研究过剩地形和同震滑坡的空间关系, 文中对2008年汶川地震、 2013年芦山地震和2014年鲁甸地震等诱发滑坡与过剩地形的空间分布进行了分析, 结果表明二者的空间分布具有高度的一致性, 显示出过剩地形对同震滑坡空间分布的控制作用。值得注意的是, 文中计算获得的泸定地震震区过剩地形的平均高度约为80.0m, 明显大于此次地震诱发滑坡的厚度, 这意味着此次同震滑坡仅仅是移除了很少部分的过剩地形, 据此推测剩余的过剩地形分布区仍是未来潜在的滑坡易发区。

关键词: 2022年M_S6.8泸定地震, 同震滑坡, 过剩地形, 滑坡分布

Abstract:

Strong earthquakes in mountainous regions are prone to triggering severe geological disasters, such as landslides, collapses, and debris flows. These disasters are characterized by their wide distribution, large scale, and high frequency, making them among the most destructive secondary effects of earthquakes. In recent years, the central and eastern parts of the Qinghai-Tibet Plateau have experienced frequent strong earthquakes, leading to varying degrees of earthquake-induced landslide disasters.
Landscape evolution is significantly influenced by tectonic activities and river incising, which alter the materials of hillslopes and their topographic characteristics. Earthquakes can significantly affect the spatial distribution of co-seismic landslides, particularly in areas with excess topography. In tectonically active zones, rock uplift and river erosion gradually increase slope angles and decrease slope stability. Weathering, freeze-thaw cycles, and seismic vibrations can reduce rock strength, leading to slope erosion and landslides. Once these processes occur, the slope tends to reach a critical state of stability, which is characterized by the presence of excess topography. Landslides can rapidly reduce hillside elevations, limiting terrain relief and impacting landform evolution. Excess topography, defined as rock mass inclined at angles greater than a specified threshold, is closely related to unstable slope masses. The essence of a landslide is the disruption of slope equilibrium, often reflected in the presence of excess topography. However, the influence of excess topography on the distribution of co-seismic landslides is not well understood.
Earthquake-induced landslides occur when slopes become unstable and slide due to seismic forces. The instability arises when ground motion alters the internal friction angle and cohesion forces along rock mass defects, making them unable to resist the gravitational forces that cause sliding. The weight of the slope material plays a crucial role in this process. As a key component of landscape evolution, landslides significantly shape geomorphic forms, as indicated by the presence of excess topography. The undulating terrain of a region is the result of long-term structural and surface erosion interactions, as well as material migration and distribution. Landslide development is closely related to the local environment, particularly geomorphic conditions. Seismic landslides also play a vital role in shaping and reorganizing active orogenic belts, influencing subsequent landscape evolution.
On September 5, 2022, a M_S6.8 earthquake struck Luding county, Sichuan province, China, with the epicenter in Hailuogou Glacier Forest Park(29.59°N, 102.08°E), at a focal depth of 16km and a maximum intensity of Ⅸ degrees. The earthquake, lasting approximately 20 seconds, was strongly felt across many parts of Sichuan Province and induced numerous landslides, causing significant damage. The affected area, located at the transition between the Qinghai-Tibet Plateau and the Sichuan Basin, features a typical alpine and canyon landscape with steep terrain and river incision, providing favorable conditions for landslides. The long-term and intense tectonic activity in the eastern Qinghai-Tibet Plateau has resulted in complex topography and geomorphology, providing the material basis and external conditions for earthquake and landslide disasters.
With advancements in science and technology, the Digital Elevation Model(DEM)has become widely used in geoscience research. As DEM accuracy improves, its applications have evolved from qualitative descriptions of geomorphic morphology to semi-quantitative and quantitative analyses of various geomorphic parameters. Geomorphic parameters reveal the structural geomorphic information within topography, essential for understanding regional characteristics and evolution mechanisms. The Luding earthquake serves as a case study for analyzing the influence of topography on the distribution of co-seismic landslides.
In this study, through post-earthquake remote sensing image analysis we identified 1 485 landslides(covering approximately 14.83km²)and analyzed their spatial distribution. Field surveys revealed that most co-seismic landslides are shallow, with relatively small thicknesses, primarily located along the Dadu River. Excess topography calculations based on the ALOS 12.5m DEM and subsequent quantitative analysis of its correlation with co-seismic landslides indicate a strong relationship: with a 30° threshold, excess topography peaks are found along the Dadu River and its tributaries, coinciding with the majority of landslide occurrences. A total of 91.7% of co-seismic landslides are within areas of varying excess topography heights. However, the average height of excess topography in landslide areas(~80m)significantly exceeds landslide thicknesses, suggesting that the Luding earthquake only mobilized a small fraction of the total excess topography. The remaining excess topography may represent potential unstable slopes for future landslides. Furthermore, the spatial distribution of landslides induced by previous earthquakes, such as the Wenchuan earthquake in 2008, the Lushan earthquake in 2013, and the Ludian earthquake in 2014, shows a high degree of consistency. This underscores the importance of understanding the relationship between excess terrain and landslide distribution to enhance the accuracy of earthquake-induced landslide predictions.

Key words: 2022 M_S6.8 Luding earthquake, seismic landslide, excess topography, landslide distribution

邱恒志, 马思远, 陈晓利. 2022年M_S6.8泸定地震诱发滑坡中过剩地形的影响[J]. 地震地质, 2024, 46(4): 783-801.

QIU Heng-zhi, MA Si-yuan, CHEN Xiao-li. STUDY ON THE EFFECT OF EXCESS TOPOGRAPHY ON LANDSLIDES INDUCED BY LUDING M_S6.8 EARTHQUAKE IN 2022[J]. SEISMOLOGY AND GEOLOGY, 2024, 46(4): 783-801.

图/表 16

图 1 研究区及其邻近区域的地质构造图红框为研究区, 活动断层数据来自文献(邓起东等, 2007)

Fig. 1 Geological structure map of the study area and its adjacent region.

图 2 泸定地震部分地区的遥感影像 a 泸定地震前; b 地震引发的山体滑坡对应的解译

Fig. 2 Remote sensing image of part impacted area of Luding earthquake.

图 3 研究区内的地层年代和泸定地震诱发的滑坡分布图

Fig. 3 Distribution map of stratigraphic chronology and landslides induced by Luding earthquake.

表1 不同尺度同震滑坡分布情况

Table1 Characteristics of coseismic landslides at different scales

分类	滑坡面积/m²	滑坡数量	比例/%
Ⅰ	面积<2000	447	30.10
Ⅱ	2000≤面积<5000	418	28.15
Ⅲ	5000≤面积<10000	257	17.31
Ⅳ	10000≤面积<50000	320	21.54
Ⅴ	面积≥50000	43	2.90
总计		1485	100

图 4 滑坡面积和密度分布情况 a 滑坡面积-概率密度分布曲线; b 滑坡密度分布情况

Fig. 4 Distribution of landslides area with seismic density.

图 5 泸定地震现场调查发现的典型滑坡

Fig. 5 Typical sites of landslides caused by the Luding earthquake.

图 6 过剩地形计算示意图(改自文献(Blöthe et al., 2015))

Fig. 6 Calculation of excess topography from 1D elevation profile(revised from Blöthe et al., 2015).

图 7 震区过剩地形分布图

Fig. 7 Map of excess topography distribution in earthquake zone.

图 8 同震滑坡和过剩地形分布与地形因素的关系 a 高程; b 坡度

Fig. 8 Relationships of distribution of coseismic landslide with excess topography and topographic factors.

图 9 同震滑坡和过剩地形分布在不同地震烈度区的分布

Fig. 9 The relationship between coseismic landslides and excess topography distribution with different seismic intensities.

图 10 AA' 剖面上过剩地形连续变化情况 a 过剩地形剖面示意图; b 过剩地形高度连续变化情况

Fig. 10 Continuous variation of excess topography along AA' profile.

图 11 过剩地形的影响因素分析 a 过剩地形体积和临界坡度的关系; b 不同地层年代的平均坡度值

Fig. 11 Analysis of influencing factors on excess topography.

图 12 不同年代地层上的过剩地形分布 R 古近-新近纪; T 三叠纪: P 二叠纪; J 侏罗纪; D 泥盆纪; S 志留纪; Z 震旦纪; Pt 元古代

Fig. 12 Distribution of excess topography at different stratigraphic chronology.

图 13 AA' 剖面中平均坡度、高程、过剩地形高度 a 平均过剩地形高度和平均坡度; b 平均过剩地形高度和平均高程

Fig. 13 Average slope, elevation and excess topography height along AA' profile.

图 14 不同地震诱发的同震滑坡和过剩地形分布 2008年汶川地震的同震滑坡数据来自文献(Xu et al., 2014); 2013年芦山地震的同震滑坡数据来文献(Xu et al., 2015)

Fig. 14 Distribution of landslide and excess terrain induced by different earthquakes.

表2 不同地震诱发的同震滑坡在过剩地形中的分布情况统计表

Table2 Statistical distribution of coseismic landslides in excess terrain induced by different earthquakes

地震	同震滑坡面积 /km²	位于过剩地形中的滑坡面积 /km²	所占面积比 /%	同震滑坡数 /个	位于过剩地形中的滑坡数 /个	所占个数比 /%
2008年汶川地震	1146.04	864.88	75.5	165025	120578	73.1
2013年芦山地震	17.16	13.76	80.2	21055	14350	68.2
2014年鲁甸地震	5.01	4.28	85.4	610	532	87.2
2022年泸定地震	14.83	13.6	91.7	1485	1383	93.1

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