Vol.2, No.3, 160-174 (2010) Natural Science http://dx.doi.org/10.4236/ns.2010.23026 Surface rupture and hazard characteristics of the Wenchuan Ms 8.0 earthquake, Sichuan, China﹡ Rong-Jun Zhou1, Yong Li2, Liang Yan2, Jian-Cheng Lei1, Yi Zhang2, Yu-Lin He1, Long-Shen Chen3, Xiao-Gang Li1, Shi-Yuan Wang1, You-Qing Ye1, Yu-Fa Liu1, Chuan-Chuan Kang 1, Tian-Yong Ge 1, Qiang He1, Wei Huang1 1Institute of Engineering Seismology of Earthquake Administration of Sichuan Province, Chengdu, China 2State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, China; [email protected] 3The University of Hong Kong, Department of Geology, Hong Kong, China Received 23 December 2009; revised 14 January 2010; accepted 25 January 2010. ABSTRACT The rate of the long axis and the minor is betw- een 8:1 and 10:1. Three Ⅺ intensity regions are Longmen Shan is located the special joint be- isolated in distribution. It presents a multipoint tween Tibetan Plateau inland in the west and instantaneous characteristic of the rupture. Yangtze craton in the east. Consisting of a se- ries of parallel imbricated thrust, it develops, Keywords: Wenchuan earthquake; Longmen Shan; from the west to the east, the Maoxian- Surface rupture; Hazard; Sichuan; China Wenchuan, Beichuan-Yingxiu and Pengxian- Guanxian faults. The Wenchuan earthquake is a thrust with strike-slip type, and thre surface 1. INTRODUCTION ruptures are located on the Beichuan-Yingxiu fault zone and Pengxian-Guanxian fault zone. According to the record of China earthquake networks, The surface rupture on the Beichuan-Yingxiu on 12th May, 2008, a huge earthquake Ms8.0 struck fault shows the thrust and dextral slip charac- Yingxiu town in Wenchuan county, Sichuan province teristic. The maximum vertical displacement of (31°00′N, 103°24′E). The earthquake took place at the surface rupture is about 10.3 m and the maxi- 14:28:04(Beijing time) and the depth of its hypocenter is mum right-lateral displacement is about 5.85m. about 14 kilometers. This earthquake with high magni- Though the vertical displacements and the hori- tude and shallow hypocenter made an astonished attack zontal displacements in the different segments on Longmen Shan area, which is located in the west of have certain differences, as a whole, the ratio of Sichuan basin, resulting in tremendous casualties and the vertical displacement and the horizontal dis- property losses. The earthquake occurred on Longmen placement is close to 1:1. The surface rupture on Shan tectonic belt at the eastern margin of the Tibet Pla- the Pengxian-Guanxian fault shows thrust and teau. Since the late Cenozoic, the thrust-dextral move- dextral characteristic. The rates of vertical dis- ment of Longmen Shan tectonic belt led to Longmen placements and the horizontal displacements Shan Mt.’s fast uplifting in opposition to Sichuan basin. ones on the most other segments are between Within the range of 50 kilometers along Longmen Shan 1:3 and 1:2. So the Beichuan- Yingxiu fault is a tectonic belt, topographical fall exceeds 5 kilometers, dextral-slip and thrust fault and the average ver- which produces mountains and canyons region [1-5]. tical displacement is equal to the average hori- The special terrain and geology condition increased the zontal displacement, while the Pengxian- Guan damage of this earthquake. xian fault is thrust fault with a little dextral-slip As soon as the earthquake occurred, the writer went to component. The total intensity area above Ⅵ de- Earthquake-stricken area to carry out an on-the-spot in- gree of the Wenchuan earthquake is about 333000 vestigation for more than twenty days, accompanying km2. The high earthquake intensity line stretches the earthquake emergency job team of China Earthquake to N40-50°E along Longmen Shan tectonic belt. Administration. Some replenish investigations were car- ﹡This research was supported by China National Natural Science ried out later. Mountain fall, the earth splits, changes of Foundation grant 40841010, 40972083 and China National Science and mountains and rivers caused by the earthquake made Technology supporting Plan Foundation grant 2006BAC13B02-07, Longmen Shan full of distress everywhere, which was 2006BAC13B01-604. Copyright © 2010 SciRes. OPEN ACCESS R. J. Zhou et al. / Natural Science 2 (2010) 160-174 161 elegant and pretty in the past. The enormous casualties average vertical slip rates of Beichuan-Yingxiu fault and and property losses that the earthquake brought about are Pengxian-Guanxian fault are less than 1 mm/yr. The furthermore grieved. Being greatly shocked and regretful, horizontal slip rates of the faults are between 1mm/yr and we illuminate the first step survey results of surface rup- 10mm/yr. And the faults show a dextral-slip characteristic. ture and hazard characteristic of the earthquake and our The Wenchuan Ms8.0 earthquake, on 12th May, 2008, thoughts about it in this paper, providing a reference for produced coseismic displacements along Beichuan- our fraternity. Especially, this paper was devoted to those Yingxiu fault and Pengxian-Guanxian fault coinstanta- who had been died or disappeared in this destructive neously. After the earthquake, a lot of geological experts earthquake. [13-23] carried out detailed investigations about the sur- face rupture, caused by the Wenchuan earthquake, in the 2. THE SURFACE RUPTURE OF THE Longmen Shan area. Therefore, it provides a good study WENCHUAN EARTHQUAKE and a validated example for the late Quaternary activity of the Longmen Shan tectonic belt. The Longmen Shan tectonic belt stretches through the central of Sichuan province at N40-50°E orientation and 2.1. The Surface Rupture on the forms the boundary of the Songpan-Garzê orogenic belt Beichuan-Yingxiu Fault and the Yangtze Platform[1,6-8]. In late Triassic, the clo- Beichuan-Yingxiu fault is also called Beichuan fault [5] sure of Neo-Tethys Ocean resulted in the Longmen Shan and is the major causative fault of the Wenchuan Ms8.0 tectonic thrusting from northwest to southeast. It con- earthquake on 12th May, 2008. The surface rupture on trolled the formation and development of the Cenozonic this fault started near by Yingxiu town in Wenchuan foreland basin in the southwest of the Sichuan basin. county and extended to the north-east. It is about 220 There is a suit of mauve late Triassic - Cenozonic clastic ， rock of river and lake facies. Since late Cenozonic, with kilometers long, and crosses Hongkou town Longmen the closure of Neo-Tethys Ocean and fast-uplift of Qing- Shan town, Donglin temple, the north of Hongbai town, hai-Tibet Plateau, neotectonic activities of Longmen Shan Qingping town, Chaping town, Leigu town, Beichuan tectonic belt have aroused many researchers’ interest. town, Chenjiaba village, Fenghuang village of Guixi Avouac and Tapponnier [9] believed that Longmen Shan town and Pingtong town, break down near Shikanzi vil- tectonic belt shortens sustainably at the NW-SE orienta- lage in the east of Nanba town, Pingwu county. tion, with a rate of 20mm/yr since late Cenozoic. But 1) The surface rupture of the Wenchuan Earthquake in through field works, Burchfiel [1] found that there was Yingxiu town lack of geological evidence for a large-scale shortening of The epicenter of Wenchuan Ms8.0 earthquake is close Longmen Shan tectonic belt and the west of Sichuan basin. to Yingxiu town. The surface rupture of the earthquake Data measured by the Global Positioning System(GPS) crosses the north of Yingxiu town in N60-70°E orienta- cross Longmen Shan tectonic belt shows that the shorten- tion. According to the different section features of the ing rate of it is only 4.0 ± 2.0mm/yr, in opposition to that surface ruptures, it can be inferred that inclination of the of Sichuan basin [10]. However, England and Molnar [11] fault is about 40-50°. In the north-west of Yingxiu town, pointed out that convergence between India plate and the vertical displacement of the national highway (G213) Eurasia plate was reflected by a simple dextral-shear mo- is about 2 meters, and the dextral displacement is about tion in the east margin of the Qinghai-Tibet Plateau. Fur- 1.7 meters. A small waterfall was produced on a river thermore, Li Yong [3] believed that uplift of the Longmen bed (Figure 2). Zhou [12] described that the vertical Shan was produced under the co-effect of the dextral mo- displacement of Minjiang river’s terrace IV caused by tion and erode load-off of the Longmen Shan tectonic Beichuan-Yingxiu fault was about 40 meters. And the belt. bending fault produced a normal fault graben on the The Longmen Shan tectonic belt is composed of hanging wall of the fault. This earthquake produced two Maoxian-Wenchuan fault (the north-eastern segment is surface rupture zones on the fault scarp (close to its top) called Pingwu-Qingchuan fault), Beichuan-Yingxiu fault with a horizontal distance of 6 meters. The vertical dis- and Pengxian-Guanxian fault. There is a blind fault in the placement is about 0.75 meters and the horizontal dis- front of the Longmen Shan Mountain (Figure 1). All of placement is 1.1 meters at the low elevation place. At the these faults are late Pleistocence-Holocene active faults. place with higher elevation, the vertical displacement There are divergent opinions on the late Quaternary ac- and the horizontal one are 2.4 meters, 1.9 meters, re- tivities of the Longmen Shan tectonic belt among differ- spectively. And the total vertical displacement is 3.15 ent scholars. Zhou [12] believe that the Longmen Shan meters; the total horizontal displacement is 3.0 meters tectonic belt shows a thrust and dextral slip since late (Figure 3).