Nat. Hazards Earth Syst. Sci., 12, 351–363, 2012 www.nat-hazards-earth-syst-sci.net/12/351/2012/ Natural Hazards doi:10.5194/nhess-12-351-2012 and Earth © Author(s) 2012. CC Attribution 3.0 License. System Sciences Earthquake-triggered landslides in southwest China X. L. Chen, Q. Zhou, H. Ran, and R. Dong Key Laboratory of Active Tectonics and Volcano, China Earthquake Administration, Beijing, 100029, China Correspondence to: X. L. Chen ([email protected]) Received: 31 May 2011 – Revised: 4 November 2011 – Accepted: 14 December 2011 – Published: 17 February 2012 Abstract. Southwest China is located in the southeastern ities were due to landslides triggered by the shaking (Yin et margin of the Tibetan Plateau and it is a region of high seis- al., 2009; Zhang, 2009). Different from the landslides caused mic activity. Historically, strong earthquakes that occurred by rainfall, earthquake-triggered landslides can take place in here usually generated lots of landslides and brought de- a comparatively wider region, and sometimes they are the structive damages. This paper introduces several earthquake- most potentially destructive amongst the secondary geotech- triggered landslide events in this region and describes their nical hazard associated with earthquakes. These large and characteristics. Also, the historical data of earthquakes with widely distributed landslides usually cannot be prevented by a magnitude of 7.0 or greater, having occurred in this region, current mitigating measures, nor can the regular measures is collected and the relationship between the affected area used to monitor or predict rainfall-triggered landslides. In- of landslides and earthquake magnitude is analysed. Based stead, the effective preventive measures are early warning on the study, it can be concluded that strong earthquakes, and evacuation of vulnerable communities. In order to mit- steep topography as well as fragile geological environment, igate the damages, researches on the potential earthquake- are the main reasons responsible for serious landslides in induced landslide zoning are being conducted in many coun- southwest China. At the same time, it is found that the re- tries at present (Jibson and Michael, 2009; Scott and Keefer, lationship between the area affected by landslides and the 2003; National Institute for Land and Infrastructure Man- earthquake magnitude in this region are consistent with what agement, Ministry of Land, Infrastructure, Transport and has been obtained worldwide. Moreover, in this paper, it is Tourism, 2004). seen that the size of the areas affected by landslides change For the assessment of earthquake-triggered landslide haz- enormously even under the same earthquake magnitude in ards, it is necessary to establish correlations between seismic the study region. While at the same tectonic place or fault ground shaking and landslides in different geological, topo- belt, areas affected by landslides presented similar outline graphical and climatic conditions (Rodr´ıguez et al., 1999). and size. This means that local geological conditions and And, the assessment can be performed at different levels historical earthquake background have an important influ- ranging from regional studies to the site-specific evalua- ence on landslides distribution, and they should be consid- tion of individual slopes aimed to different demands (ISS- ered when assessing earthquake-triggered landslide hazards MGE, 1999; Australian geomechanics society landslide zon- at Grade 1 according to ISSMGE. ing working group, 2007; Bommer et al., 2002). Keefer com- piled an earthquake-triggered landslides database which in- cluded 40 historical world-wide earthquakes and, based on 1 Introduction it, he studied the characteristics, geological environment of landslides, as well as the relations between landslide distri- As a kind of secondary disaster caused by strong earth- bution and seismic parameters (Keefer, 1984). Rodriguez quakes, earthquake-triggered landslides have drawn much extended Keefer’s work with other 36 world-wide earth- attention in the world because of severe hazards it causes. quakes and used the similar approach to analyse his new data. In a mountainous region, sometimes a great loss of lives The knowledge obtained by Keefer and Rodr´ıguez are very and properties caused by landslides even exceeds the losses similar except the presence of extreme outliers in some of caused by the earthquake itself. For example, in the the correlations (Rodr´ıguez et al., 1999). The relationships Wenchuan earthquake of 12 May 2008, almost 20 000 fatal- between the area of landslides and earthquake magnitude Published by Copernicus Publications on behalf of the European Geosciences Union. 352 X. L. Chen et al.: Earthquake-triggered landslides in southwest China should be the simplest and most important method in eval- uating earthquake-triggered landslide hazards: the hazard is expressed as a binary function defining geographical limits within which landslides will be expected from an earthquake of specified magnitude and location (Bommer et al., 2002). In Southwest China, due to its complex geological and geographical conditions, many strong earthquakes occurred frequently and are accompanied by a large number of land- slides that was associated with the serious damage (Yi et al., 2002; Xu et al., 2005; Chen et al., 2010; Wang et al., 2009; Wen et al., 2004). For example, the destruction caused by landslides during Wenchuan Earthquake in China in 2008 was unexpected and shocked the world. This earth- quake not only caused an amount of landslides of more than 15 000 (Yin et al., 2009), also, it triggered some infrequent huge landslides along the seismic faults. Daguangbao land- slide with estimated volume of 750 million m3 is the largest one among the individual landslides triggered by Wenchuan earthquake (Huang et al., 2009). Similarly, landslides caused by the Diexi earthquake in 1933 formed a large dam on the Min river, and later this dam collapsed and inundated the downstream region, resulting in thousands of deaths. Ob- viously, as a secondary seismic disaster, earthquake-induced landslides in the southwest China clearly constitute an im- portant factor of the high level seismic risk to which the pop- ulation and fragile environment of this region are exposed. According to the latest earthquake statistics, there are 835 earthquakes with magnitude 4.7 or greater which oc- curred in the study area (Earthquake Disaster prevention de- partment of State Seismological Bureau, 1995; Earthquake Disaster prevention department of China Earthquake Admin- istration Bureau, 1999). Therefore, the data of landslides which occurred with these earthquakes would enrich the worldwide landslides database. Limited to incompleteness of historical documents, this paper will present just a part of earthquake-triggered landslides in southwest China and de- Fig. 1. Distribution of the main faults and structural basins in south- scribe several earthquakes which triggered many landslidesFig 1. Distribution of the main faults and structural basins in southwest China (revised from Southwest China west China (revised from Southwest China Intensity Zoning Team in the modern time and had formal post-earthquake investiga- of State SeismologicalIntensity Zoning Bureau), Team of State (1) LongmenshanSeismological Bureau) fault; (2) Emei- tions. Despite of imperfect data, earthquake-triggered(1) Longmenshan land- Jinyang fault; (2) fault; Emei-Jinyang (3) Lianfeng-Qiaojia fault; (3) Lianfe fault;ng-Qiaojia (4) fault; Yiliang-Shuicheng (4) Yiliang-Shuicheng fault; (5) slides of southwest China provided in this paper willMile-Shizong supple- fault;fault; (6) Puxionghe (5) Mile-Shizong fault; (7) Xiluohe fault; fault; (6) (8) Puxionghe Luoxi fault; fault;(9) Xiaojiang (7) Xiluohe fault; (10) Zemuhe fault; ment the previous researches, as well as the worldwide(11) Anninghe data fault;fault; (12) (8) Nanhe Luoxi fault; fault; (13) Ninghui (9) Xiaojiang fault; (14) fault;Qujiang (10) fault; Zemuhe (15) Shiping-Jianshui fault; fault; (16) for a better understanding in landslide hazard. Also, the re- Mopanshan-Lvzhijiang(11) Anninghefault; (17) fault; Xianshuihe (12) Nanhe fault; fault; (18) (13) Litang Ninghui fault; fault; (19) (14) Xiaojinhe Qu- fault; (20) sults obtained in this study will be a preliminary step in fur- jiang fault; (15) Shiping-Jianshui fault; (16) Mopanshan-Lvzhijiang Jinhe-Yongsheng-Binchan fault; (21) Yuanjiang fault; (22) Jinshajiang fault; (23) Lancangjiang fault thering the study on influencing factors related to landslide fault; (17) Xianshuihe fault; (18) Litang fault; (19) Xiaojinhe fault; (20) Jinhe-Yongsheng-Binchan fault; (21) Yuanjiang fault; (22) Jin- hazard assessment at the region scale. shajiang fault; (23) Lancangjiang fault. 2 Regional setting 2.1 Geology and geomorphology The study region called Southwest China is located in the southeastern margin of Tibetan Plateau. This research actu- The present structural outline of southwest China has re- ally focuses on a slightly larger area from 99–105◦ E and 23– sulted from the combination of Indo Sinian orogenesis, Yan- 33◦ N, which includes the western part of Sichuan province shan detachment movement and the Himalayan thrust nappe and the eastern part of Yunnan province in China (Fig. 1). movement. From the Cenozoic era, features of the fault blocks, which formed during Indo Sinian orogenesis and Nat. Hazards Earth Syst. Sci., 12, 351–363, 2012 www.nat-hazards-earth-syst-sci.net/12/351/2012/ X. L. Chen