Landslide distribution and size versus relative relief (Shaanxi Province, China) Haijun Qiu, Peng Cui, Amar Deep Regmi, Sheng Hu, Yuzhu Zhang & Yi He Bulletin of Engineering Geology and the Environment The official journal of the IAEG ISSN 1435-9529 Bull Eng Geol Environ DOI 10.1007/s10064-017-1121-5 1 23 Your article is protected by copyright and all rights are held exclusively by Springer- Verlag GmbH Germany. This e-offprint is for personal use only and shall not be self- archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy Bull Eng Geol Environ DOI 10.1007/s10064-017-1121-5 ORIGINAL PAPER Landslide distribution and size versus relative relief (Shaanxi Province, China) 1,2,3 3 3 1 1 Haijun Qiu • Peng Cui • Amar Deep Regmi • Sheng Hu • Yuzhu Zhang • Yi He1 Received: 12 April 2017 / Accepted: 4 July 2017 Ó Springer-Verlag GmbH Germany 2017 Abstract The present study aims to investigate the dis- certain size threshold. Below this value, it exhibited an tribution and size of landslides in relation to relative relief. obvious rollover effect. Further analysis has shown that For this, a landslide inventory map of the area was landslide cumulative frequency-area curve is strongly developed from the interpretation of satellite images and influenced by relative relief. The rollover effect is more detailed field survey. From this we could map 331 land- obvious with the increase of relative relief. The exponent slides in Ningqing County (Shaanxi Province). By using of power law correlation gradually increased from 0.993 to GIS and statistical approaches, we studied the coupling 1.872 with increasing relative relief. between landslide size distribution and relative relief. From this the control of relative relief on the rollover effect of the Keywords Landslides size and size distribution Á Satellite size distribution of landslides is obtained. The result shows imagery Á GIS Á Relative relief Á Rollover effect Á China that the landslide frequency-relative relief distribution is unimodal, with majority of landslides occurring in areas with relative reliefs in between 300 and 400. The relative Introduction number density of landslides decreased with the increase in the relative relief; on the contrary, the average area, aver- Landslide is one of the most widespread natural hazards age length and average width of landslide increased with responsible for many fatalities, as well as high levels of the increase in relative relief. The percentage of large-scale economic loss and social damage in many parts of the landslide increased with the increase of relative relief or world annually (Lee and Jones 2004; Mansour et al. 2011; vice versa. In addition, the cumulative frequency-area Massey et al. 2013). In many countries, landslides lead to distributions of these landslides empirically agree well with greater casualties and economic losses than other natural a power-law relation with an exponent of 1.776 above a hazards such as floods, earthquakes, volcanic eruptions, and severe storms (Schuster and Fleming 1986; Alexander 1989; Glade 1998; Guzzetti et al. 2002). Moreover, the occurrence of damaging landslides have substantially increased worldwide during recent decades in developing countries because of rapid population growth, uncontrolled urban sprawl, continued deforestation, and increased & Haijun Qiu regional precipitation in landslide prone areas due to cli- [email protected] mate change (Broothaerts et al. 2012; Conforti et al. 2014; 1 College of Urban and Environmental Science, Northwest Greco et al. 2013). University, Xi’an 710127, China It is extremely important to make clear the size dis- 2 Institute of Earth Surface System and Hazards, Northwest tribution of landslides in order to quantify the occurrence University, Xi’an 710127, China of landslides, as well as to understand correctly and 3 Institute of Mountain Hazards and Environment, Chinese characterize the hazard associated with the regional Academy of Sciences, Chengdu 610041, Sichuan, China landslide distribution and estimate the integrated effects 123 Author's personal copy H. Qiu et al. of these hazards (Stark and Hovius 2001; Guthrie et al. Regional setting 2008). It is very widely accepted that a landslide of a given size cannot exceed the relief of the landscape in The Ningqiang County is bounded by longitudes which it occurs (Schmidt and Montgomery 1995; 105°2101000E to 106°3501800E and latitudes of 32°3700600N Guthrie et al. 2008). Relative relief, which is taken as and 33°1204200N extending for 3246.8 km2 in southwest the most basic natural geographical factor restricts the Shaanxi province of China (Fig. 1). The area is located in matter and energy of earth surface redistribution (Zhou the cross belt of Qin Mountain in the north and Daba et al. 2012). Numerous studies have taken relative relief Mountain in the south. Elevation in the area ranges from as an important causal factor to analysis the landslide 520 m to 2103.7 m above mean sea level (amsl). The area susceptibility and hazard (Dai et al. 2001;Confortietal. with slope gradients greater than 25° accounts for 58.85% 2014). However, less attention has been given to the of the total study area. The drainage network was generated comprehensive and systematic analysis of the quantita- from the digital elevation model (DEM) using hydrology tive relationship between relative relief and landslide tools of the ArcGIS software. The river network has a size, especially how relative relief can influence the dendritic pattern with 1.4 km-1 drainage density, which frequency-size distribution and its rollover effect. indicates that the area is structurally controlled by a dense Published literature has shown that frequency-size drainage network system (Fig. 1). Landslide occurrence is distribution of landslides generally exhibit power-law related to the drainage system of the area; with majority of scaling over a limited scale range because of the prop- landslides occurring in the proximity to drainage network erty of self-similarity. However, a large proportion of the (Fig. 1). The climate in the area is warm temperate and landslide data sets do not fit a simple power law rela- humid continental monsoon zone, with average annual tionship (Fuyii 1969; Stark and Hovius 2001;Daiand precipitation of 920.54 mm and average temperature of Lee 2001; Malamud et al. 2004a, b; Guthrie and Evans 12.9 °C (from the data of 1961 to 2012). Precipitation is 2004a, b, 2005). Landslide cumulative frequency size most abundant in the months of July–September; with a often departs from the power law relationship and mean annual rainfall of 581.76 mm at the Ningqiang rain exhibit a so-called rollover effect in the low size range gauge (Fig. 2). Concentrated rainfall patterns result in a (Hungr et al. 2008). Typical explanation for the rollover great number of landslides, mostly occurring during is data biasing which suggests that small landslides have intense, short-duration rainfall. Most of the landslides are been undercounted among other things, so artificially located at the southeast aspect, as major rainfall come from reducing the probability of small landslides (Hungr et al. the southeast. 1999;Brardinonietal.2003; Malamud et al. 2004a, b). Tectonically, the study area spans over the south Bashan For example, smaller landslides cannot be inventoried Fold Belt in the Yangtze plate and the north orogenic belt because identification by remote sensing is hampered by in Songpan-Ganzi. Based on the boundary of Jinshan the forest canopy in densely forested areas (Brardinoni Temple-Yangpingguan-Mianxian Great Fault (JYMF), the and Church 2004). But some authors proposed physical south of the county belongs to the Yangtze Plate, and the explanations for the rollover such as soil moisture vari- north belongs to the Songpan-Ganzi orogenic belt (Fig. 3). ability, interaction with topography, overall physio- Lithology in the area varies from south to north and the graphic variables of the landscape, and slope geometry area is demarcated by complex geological structures. The (Pelletier et al. 1997;Turcotteetal.2002; Guthrie and main stratigraphic units are Bikou Petrofabric, Dengying Evans 2004a, b; Guthrie et al. 2008; Hungr et al. 2008). Formation, Longmaxi Formation, Shipai Formation, However, the interaction between rollover effect and Luoreping Formation Maoxian Group Nantuo Formation, relative relief is poorly understood. and Chenjiaba Formation. Quaternary deposits consist of In this paper we have described the interdependent rela- river terraces. A majority of landslides were observed tionship on parameters of landslides based on an inventory within the Bikou Petrofabric. The main rock types are map of 331 landslides using statistical methods and geo- schist, slate, phyllite, shale, conglomerate, siltstone, and graphic information systems. We evaluated the role of rel- spilite. The study area lies within an active tectonic setting ative relief in determining landslide frequency and relative with many fault, thrust and folds. The main geological number density. We have also determined the relationship structures demarcating this area are JYMF, Kuanchuanpu between relative relief and landslide size. Furthermore, we fault and Dazhuba-Xinji fault (Fig. 3). The JYMF passes examined cumulative frequency-area distribution within through the northwestern part of the study area. This area different relative relief, discussed the rollover effect of fre- has also undergone local folding of different scales, dis- quency-area distribution, and elucidated how relative relief playing many synclines, anticlines and continuous folding.