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Spatial distribution of landslides triggered by the 2013 Lushan “4.20” Ms 7.0 earthquake in relation to the blind thrust fault

2014/5/27 10:15:22

Xu Chong et al. of the Key Laboratory of Active Tectonics and Volcano carried out visual interpretation of the landslides triggered by the Lushan “4.20” Ms 7.0 earthquake based on available high-resolution aerial photos acquired after the earthquake (the total cover area is about 2885 km2) and in the light of the relevant standards. In the end,3883 landslides (Fig. 1) were identified. Most of them are small rock collapses, soil collapses and rock slides. An overwhelming majority of the landslides is within a limit area and a tiny minority is outside this area. They are small soil collapses or slides developed on the slope masses sensitive before the earthquake.

Fig. 1  Distribution of landslides triggered by Lushan earthquake

Based on a search radius of 500m, a density map of landslide distribution points was prepared (Fig. 2). The map indicates most of the areas with a density of above 5 landslides/km2are distributed in the mountainous areas in the north and northwest of the epicenter, which are not only located on the hanging side of the Lushan earthquake but also affected by the 2008 Wenchuan Ms 8.0 earthquake, completely consistent with the fast judgment we made after the earthquake. In the “Lushan County – Longmen Township – Baosheng Township” area, many earthquake-induced landslides are observed too. This supports the inference that the seismogenic fracture is not the Shuangshi – Dachuan fault. Although we cannot deny the important role of this fault in this earthquake, no obvious surface rupture was generated along this fault. The latest observations suggest that the Lushan earthquake is a typical blind thrust faulting (Xu Xiwei et al., 2013, Chinese Science Bulletin). In Longmen Township of Lushan County, some signs of a suspected surface rupture were found (Han Zhujun, 2013). These tectonic explanations and phenomena all indicate the area between the Shuangshi – Dachuan fault and Dayi fault experienced intense deformation during this earthquake. Our result on spatial distribution of coseismic landslides also proves this point from the perspective of earthquake-induced landslides.

Fig. 2  Density distribution of landslides induced by the 2013 Lushan earthquake

Outlook: Limited by remote sensing data, this result is preliminary. According to the present result, it may be estimated that there are a great number of landslides triggered by the Lushan earthquake in the area around Shuangshi Town, Dachuan Town, the mountainous area in the west and other areas without remote sensing data. We will supplement these areas in the follow-up work. The identification of landslides in this article is for their positions only. Their boundaries will be delineated in the future.

We thank the Institute of Remote Sensing and Digital Earth of CAS, Sichuan Bureau of Surveying, Mapping and Geoinformation and the Institute of Optics and Electronics of CAS for providing data of aerial photos (the data range of each organization is shown in Fig. 1).