Engineering Geology 133–134 (2012) 40–42

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Discussion

Comment on “Spatial distribution analysis of landslides triggered by 2008.5.12Wenchuan Earthquake, China” by Shengwen Qi, Qiang Xu, Hengxing Lan, Bing Zhang,Jianyou Liu [Engineering Geology 116 (2010) 95–108]

Chong Xu⁎, Xiwei XuKey Laboratory of Active tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, PR China

A R T I C L E I N F O

Article history:Received 29 December 2011Received in revised form 24 February 2012Accepted 26 February 2012Available online 3 March 2012

Keywords:Wenchuan earthquake triggered landslidesLandslide inventorySpatial distributionStatistical analysisResonance effect

Landslides triggered by the 2008 Wenchuan earthquake have re-ceived much attention after the earthquake due to the tragic loss oflife and economic devastation caused by them. The correlation be-tween landslide occurrences and distance from seismogenic fault isimportant for understanding the spatial distribution of landslides,and the paper written by Shengwen Qi et al. presented an interestingresult in this regard. However, we have some uncertainties to discusswith the authors.

Fig. 6 in “Spatial distribution analysis of landslides triggered by2008.5.12 Wenchuan Earthquake, China” showed the frequency his-togram of landslides occurring within every 5 km distance to the sur-face rupture along the Yingxiu–Beichuan fault (F2). It showed morelandslides occurred in the block located between F2 and F3 thanthat in the hanging wall of the seismogenic fault of F2, and ShengwenQi et al. thought that this is maybe the result of resonance of the blockbetween F2 and F3 under the combination movement of the seismo-genic faults F2 and F3 and then the motion there is amplified.

As stated in Harp et al. (2011), a detailed and accurate landslideinventory is an essential part for seismic landslide spatial analysisand an ideal landslide inventory would include all of the landslidesthat are possible to detect down to size of 1–5 m in length. Basedon the guideline, a detailed Wenchuan earthquake-triggered land-

⁎ Corresponding author.E-mail address: xc11111111@126.com (C. Xu).

0013-7952/$ – see front matter © 2012 Elsevier B.V. All rights reserved.doi:10.1016/j.enggeo.2012.02.017

slides inventory is constructed. The final result shows that morethan 197,000 landslides, with a total area about 1160 km2, weredelineated from visual interpreting of high resolution satellite im-ages and aerial photographs, and verified by selected field checking.These landslides are disturbed in an area of more than 110,000 km2

(Figure 1). Before the landslide inventory finished, two incompletelandslide inventories compiled by the first author were respectiveused in Xu et al. (2009a) and Dai et al. (2011). Hereafter, weobtained many remote sensing images in higher resolution. Hugeupdates were carried out on landslide visual interpreting and a suf-ficiently detailed and accurate landslide inventory map is con-structed subsequently.

Based on the latest landslide inventorymap, the variations of land-slide occurrences with distance from the Yingxiu–Beichuan fault (F2)are created using landslide distribution spatial statistical method. Asshown in Fig. 1, Yingxiu–Beichuan co-seismic surface rupture isabout 240 km long (Xu et al., 2009b). Take 30 km extensions foreach side of the Yingxiu–Beichuan surface rupture along the Ying-xiu–Beichuan fault to create buffer zones. Buffer zones of 5 km band-width for Beichuan–Yingxiu fault are created similar as Shengwen Qiet al. for carrying out more convenient comparisons (as shown inFigure 1). All the buffer zones composed an approximate rectangularregion, about 300 km length and 140 km width. In our statistics fourindices, such as, landslide area, landslide number, landslide area per-centage (LAP), and landslide number density (LND) are used to revealcorrelations of landslide occurrence with distance from the Yingxiu–Beichuan fault. Table 1 shows the statistical result data. Fig. 2 showsthe variations of landslide occurrences with distance from the Ying-xiu–Beichuan fault. All of the four indices show much more landslideoccurrences in the hanging wall of the seismogenic fault (Yingxiu–Beichuan fault) than that in the block located between F2 and F3,which is a thoroughly different tendency in comparing with Sheng-wen Qi et al. Similar situations were appeared in the 1999 Chi-Chiearthquake (Khazai and Sitar, 2003; Lin and Tung, 2003; Wang etal., 2003; Lee et al., 2008) and the 1989 Loma Prieta earthquake(Keefer, 2000) triggered landslide events.

In our opinions, similar to other thrust-fault caused earthquaketriggered landslide events, more landslides occurred in the hangingwall of the seismogenic fault in the 2008 Wenchuan earthquakeevent. There is no resonance effect on landslide occurrences of theblock between F2 and F3 combination movement, or the resonanceeffect on landslide occurrences is rather small.

Fig. 1. The 2008 Wenchuan earthquake triggered landslide inventory map.

Table 1Landslide statistical data with distance from the Yingxiu–Beichuan fault.

Classifications/distance from F2 Area of class/km2 Landslide area/km2 Landslide number LAP/% LND/landslides/km2

−110 km 1509.029 0.198 48 0.013 0.032−105 km 1509.445 0.311 52 0.021 0.034−100 km 1510.008 0.909 84 0.060 0.056−95 km 1510.584 0.314 60 0.021 0.040−90 km 1511.239 0.550 114 0.036 0.075−85 km 1512.002 0.489 90 0.032 0.060−80 km 1512.804 0.939 177 0.062 0.117−75 km 1513.641 1.559 230 0.103 0.152−70 km 1514.638 1.429 262 0.094 0.173−65 km 1515.731 2.091 460 0.138 0.303−60 km 1517.059 3.821 760 0.252 0.501−55 km 1518.509 5.322 1041 0.350 0.686−50 km 1520.357 7.410 1481 0.487 0.974−45 km 1522.576 10.018 1824 0.658 1.198−40 km 1525.537 20.546 3130 1.347 2.052−35 km 1528.791 43.446 6662 2.842 4.358−30 km 1533.197 62.272 8772 4.062 5.721−25 km 1539.423 75.293 10971 4.891 7.127−20 km 1545.636 92.060 15726 5.956 10.174−15 km 1551.406 151.210 25116 9.747 16.189−10 km 1559.341 200.836 30719 12.880 19.700−5 km 1568.869 244.819 39380 15.605 25.1015 km 1568.026 106.561 20615 6.796 13.14710 km 1557.116 57.767 12816 3.710 8.23115 km 1550.369 30.837 7277 1.989 4.69420 km 1545.422 9.102 1937 0.589 1.25325 km 1541.860 2.737 586 0.178 0.38030 km 1538.474 1.402 303 0.091 0.197Total 42851.088 1134.249 190693 2.647 4.450

41C. Xu, X. Xu / Engineering Geology 133–134 (2012) 40–42

Fig. 2. Variations of landslide occurrences with distance from the Yingxiu–Beichuan fault (F2), (A): variations of landslide area and landslide number with distance from F2;(B) variations of LAP and LND with distance from F2.

42 C. Xu, X. Xu / Engineering Geology 133–134 (2012) 40–42

Acknowledgments

This research is supported by the National Science Foundation ofChina (Grant nos. 40821160550 and 40974057), and the Internation-al Scientific joint project of China (Grant no. 2009DFA21280).

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