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Spatial distribution of the landslides triggered by the 20 April 2013 Lushan Ms7.0 earthquake and their relation to blind thrust fault structure

2014/5/27 9:34:54

Xu Chong et al. of the Key Laboratory of Active Tectonics and Volcano carried out visual interpretation of the landslides triggered by Lushan “4.20” Ms7.0 earthquake based on available high-resolution aerial photos after the earthquake (the total cover area after deduction of overlapped regions is about 2885 km2) and in the light of the standard for visual interpretation of earthquake-induced landslides established through field study after the earthquake. In the end,3883 landslides (Fig. 1) were determined. Most of them are small rock collapses, soil collapses and rock slides. An overwhelming majority of the landslides is within the landslide limit area and a tiny minority of the landslides is outside this area. They are small soil collapses or slides developed on the slope masses sensitive before the earthquake.

Fig. 1  Distribution map 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 and they are not only located on the hanging side of Lushan earthquake but also were affected by the 2008 Wenchuan Ms8.0 earthquake before Lushan 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 developed too. This preliminarily confirms from the perspective of earthquake-induced landslides that the seismogenic fracture is not the “Shuangshi – Dachuan fault”. Although we can’t deny the important role “Shuangshi – Dachuan fault” might have played a role in this earthquake, no obvious surface rupture was generated along this fault. The latest result suggests Lushan earthquake is a typical blind thrust faulting event (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 strong deformation during this earthquake. Our result in spatial distribution of coseismic landslides also proves this point from the perspective of earthquake-induced landslides.

Fig. 2  Density map of quantity of the 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 many 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 identification of landslide positions only. The identification of landslide boundaries will also be completed in the future.

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).