International Journal of Geosciences, 2010, 21-31
doi:10.4236/ijg.2010.11003 Published Online May 2010 (
Copyright © 2010 SciRes. IJG
Surface Rupture and Hazard of Wenchuan Ms 8.0
Earthquake, Sichuan, China
Yong Li1, Runqiu Huang2, Liang Yan1, Alexander L. Densmore3, Rongjun Zhou4
1State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,
Chengdu University of Technology, Chengdu, China
2State Key Laboratory of Geo-hazard Prevention & Geo-environment Protection,
Chengdu University of Technology, Chengdu, China
3Institute of Hazard and Risk Research and Department of Geography, Durham University, Durham, UK
4Institute of Earthquake Engineering, Seismological Bureau of Sichuan Province, Chengdu, China
Received March 25, 2010; revised April 19, 2010; accepted May 13, 2010
Longmen Shan is located the special joint between the Qinghai-Tibetan Plateau in the west and the Yangtze
craton in the east. Consisting of a series of parallel imbricated thrust, it develops, from the west to the east,
the Maoxian-Wenchuan, Yingxiu-Beichuan and Pengxian-Guanxian faults. Wenchuan Ms 8.0 earthquake is
a thrust with strike-slip type, and surface ruptures are located in Yingxiu-Beichuan fault zone and Peng-
xian-Guanxian fault zone. Based on the geological background, tectonic setting, the active tectonics of Long-
men Shan and surface ruptures of the Wenchuan earthquake, a dynamical model to illustrate possible links
between surface processes and upward extrusion of lower crustal flow channel at the eastern margin of the
Tibetan plateau have been studied, and the results is the material in lower crust in the Longmen Shan moving
as nearly-vertical extrusion and uplift, resulting in the surface rate of tectonic movement differing according
to depth rate as well as the occurrence of large shallow Wenchuan earthquake.
Keywords: Wenchuan Earthquake, Longmen Shan, Surface Rupture, Hazard, Sichuan, China
1. Introduction
The Ms 8.0 Wenchuan Earthquake in May 12th, 2008 is
one of the most disastrous earthquakes since the founda-
tion of P. R. China, which destroyed not only the epi-
center of Sichuan province but also several closed prov-
inces. It was felt in most regions of China, as well as
nations outside China. This tragic event provides the
opportunity to advance the subject of seismic sciences.
Based on our accumulated activitiy on active tectonics
in Longmen Shan area, we have undertaken several new
field surveys, including international collaborative ef-
forts after the earthquake. This paper compiles 70 sets of
data from accumulated past and new surveys, detailing
surface rupture and seismic disasters since our work be-
gan in the 1990s [1-15].
2. Geological Structure in Longmen Shan
Seismic Belt
Longmen Shan is located the special joint between the
Qinghai-Tibetan Plateau in the west and the Yangtze
craton in the east, which is a foreland basin and orogeny
system with a complex structure and unique structural
history. In the depth, it is located in structural transform
belt of southwest China and the south part of Helan-
shan-Longmen Shan. To the northwest, there is thicken
crust and thicken mantle area; and to the southeast, there
is thin crust and thin mantle area in Sichuan basin. From
the Longmen Shan foreland basin to the plateau, the
crust is thickening roughly and forms a belt with west-
ern-cline belt; the central line of the belt is located the
position of Longmen Shan thrust under the surface. Com-
paring with its surface position, the line moves some
distance to the west, which suggests that Longmen Shan
thrust dips to the west and does not have a mountain root.
It also suggests that Longmen Shan is an Intracontinental
This research was supported by National Natural Science Foundation o
China grant 40841010 and CGS grant 1212010918010.
22 Y. LI ET AL.
mountain chain and an independent tectonic uploading
The isostatic gravity anomaly in Longmen Shan and
joint regions show that the crust in this area is still unsta-
ble. The figures in Longmen Shan are positive and the
figures in Longquan Shan and the area to the east are
negative while the figures in the area between them are
around zero. Since the Cenozoic, at least 5-10 km strata
have eroded in uplift rate of 0.6 mm/a. The survey data
in recent years shows that there is an uplift rate in
0.3-0.4 mm/a in Jiuding Shan [1,16].
According to the regional geological setting, this area,
from northwest to southeast, consists of Songpan-Ganzi
Orogeny (main part), Longmen Shan thrust belt, foreland
basin and forebulge; all of these four parts form a com-
plete tectonic system. We would introduce the east mar-
gin of Qinghai-Tibetan Plateau as three geological units:
Songpan-Ganzi orogenic belt (main part), Longmen Shan
thrust belt and foreland basin [1-15].
3. Surface Rupture of the Wenchuan
After the earthquake, a number of research institutions
have published basic parameters and focal mechanisms.
However, those data are different depending on different
sources and methods. The USGS recorded that the Mw.
is 7.9, the epicenter is located in Yingxiu, Wenchuan
(31.099, 103.279), the focal depth is 19 km, the rupture
length is 300 km and the duration is 120 seconds, trend-
ing 229° and fracture plane dipping 33° with strike-slip.
According to the basic parameters and the focal mecha-
nism solution, the Wenchuan earthquake had the follow-
ing two characteristics: 1) it was a shallow hypocenter
earthquake and took place in the brittle-ductility trans-
form belt in 12 km-19 km depth with enormous destruc-
tivity; 2) it belongs to thrusting and dextral strike-slip
one and from southwest to northeast, it propagated in one
direction. The release process of strain was relatively sl-
ow and may have led to a greater intensity of aftershocks
and longer duration. The intensity of the earthquake had
an oval-shaped distribution and its long axis was in a
northeast direction. In this direction, the casualties and
property loss was much bigger than other directions.
According to the surface rupture survey (Figure 1) af-
ter the earthquake, the Wenchuan earthquake faults have
characteristics of fragile, post-earthquake surface linear
image is apparent, cutting a wide range of terrain units.
They are located in Yingxiu-Beichuan fault zone (central
zone), Pengxian-Guanxian fault zone (front fault) which
only a small amount of surface rupture are found and
Maoxian-Wenchuan fault zone (back fault) which sur-
face rupture have not yet been found. Those surface rup-
ture extend in northeast direction (in NE 30º-70º, most in
NE 50º-60º) and trend to northwest (30º-80º). They dis-
tribute along the striking in a few meters to 200 meters
range and were also distributed along the Yingxiu-Beich-
uan fault and Pengxian-Guanxian fault.
Figure 1. Distribution of surface rupture of Wenchuan Earthquake in Longmen Shan.
Copyright © 2010 SciRes. IJG
Copyright © 2010 SciRes. IJG
3.1. Surface Rupture of Yingxiu-Beichuan Fault
The Yingxiu-Beichuan fault (Figures 1-3) is the Wen-
chuan earthquake’s main earthquake fault. The linear
characteristics of the earthquake surface rupture belt are
apparent. It starts from Yingxiu, Wenchuan in the south-
west and then extends to Hongkou, Longmen Shan town
(Baishuihe), Donglinsi, Hongbai, Qingping, Chaping,
Leigu, Beichuan, Chenjiaba, Guixi, and then ends in
Shikanzi, Pingwu, a distance of about 220 km. It was
distributed along the strike of Yingxiu-Beichuan fault
and disappears in the southwest 10 km of Yingxiu, be-
longing to the single-side and multi-point type rupture
with thrust characteristics. Its plane had a steep dip angle
and cut a wide range of terrain units, including mountain
bedrocks, river terraces, alluvial fans, highways and bri-
dges with bridge collapse or road displacement. Its ver-
tical offsets were in the range of 1.60-6.20 m and its
horizontal offsets were in the range 0.20-6.50, striking
NE 30°-50° and trending northwest. The average vertical
offset was 3.4 m and horizontal 2.9 m, the biggest offset
being 10.3 ± 0.2 m in Maoba, Beichuan (vertical fault)
and 6.8 ± 0.2 m in Leigu (horizontal offset). The ratio
between thrust and dextral strike-slip components are 1:1,
indicating the existence of thrust movement and dextral
strike-slip movement, the amount of thrust movement
being equal to the dextral strike-slip movement.
Basing this and according to the current surface data
obtained from the survey, we calculated vertical and
horizontal offsets in four parts of Yingxiu-Beichuan sur-
face rupture. The preliminary analysis results are: 1) the
epicenter located in the vicinity of Yingxiu (Figure 1) is
Figure 2. The vertical displacement along the Yingxiu-Beichuan Fault in Wenchuan Earthquake.
Figure 3. The horizontal displacement along the Yingxiu-Beichuan fault in Wenchuan Earthquake.
Copyright © 2010 SciRes. IJG
not the position where the biggest offset is located; the
biggest vertical and horizontal offsets are 10.3 ± 0.2 m
(vertical offset) and 6.8 ± 0.2 m (horizontal offset) in
Beichuan. According to Wenchuan earthquake focal me-
chanisms solution, the greatest offset of the main shock
is 9 m-10 m. As a result, the surface rupture is smaller
than the biggest displacement under ground; the biggest
offset are 60%-70% of the biggest offset under ground; 2)
by surface offsets, the Yingxiu-Beichuan fault can be
divided into two high-value and two low-value zones.
The two high-value zones are located in the southern part
of Hongkou, Yingxiu and the northern part of the Leigu,
Beichuan-Dengjiaba area and the two low-value zones
are located in mid-south part of the Baishuihe-Chaping
area and Huangjiaba-Shikanzi, Pingwu area. These four
sections are divided by Xiaoyudong fault, Leigu fault
and Dengjiaba fault; the two high-value areas being cau-
sed by the Xiaoyudong and Leigu faults; 3) Chen [17]
use the global seismic network data to confirm two larg-
est static sliding displacement areas, which are located at
area between epicenter and northeast 100 km to the epi-
center and 150 km northeast of the epicenter; the two
largest displacement of the slip surface locate in the two
high-value areas, indicating that the largest displacement
in the surface are the response to the displacement under
ground; 4) compared the surface rupture of earthquake
with before, the places in Yingxiu, Leigu, Baishuihe and
Gaoyuan with historical earthquake rupture are also the
places with new rupture[3-8,12,15]. In the places with
historical earthquake since Quaternary, there will be new
strong earthquake in the future.
3.2. Surface Rupture of Pengxian-Guanxian
The Pengxian-Guanxian fault (Figures 1 and 4) expe-
rienced surface fractures in this earthquake. The surface
rupture started from Xiang’e, Dujiangyan and extended
to Cifeng, Pengzhou, Bailu, Jinhua, Hanwang and Sang-
zao over a total distance of about 40-50 km, character-
ized by dextral strike-slips shortening with steep dipping.
The hanging wall was in the northwest and its foot wall
in the southeast. The vertical offset was 0.39-2.70 m and
the horizontal offset was 0.20-0.70 m (the average verti-
cal offset was 1.6 meters with an average horizontal off-
set of 0.6 meter), indicating the existence of thrust dis-
placement and dextral strike-slip displacement and thrust
displacement is greater than the dextral strike-slip dis-
placement, showing thrust and shortening characteristics.
Compared with the surface rupture of the Yingxiu-Be-
ichuan, the fault rupture is far less than the Beichuan-
Yingxiu fault rupture and it has a relatively short length
of the rupture and vertical offset; and on the other hand,
the horizontal offset dispalcement is relatively small, the
thrust displacement is main.
3.3. Surface Rupture of Xiaoyudong Fault
The fault (Figures 1, 5 and 6) is located between Ying-
xiu-Beichuan fault and Pengxian-Guanxian fault and is a
new fault being discovered after the earthquake, showing
that the fault is a transformed fault between the Ying-
xiu-Beichuan fault and the Pengxian-Guanxian fault. The
fault, striking south-north, extends about 15 km through
Xiaoyudong Bridge; the stretch of the surface rupture is
stable and we have confirmed more than 10 rupture
points. The southwest block is a hanging wall and the
northeast block is foot wall with an average vertical
offset of 1.0 meter and an average horizontal offset of
2.3 meters (vertical offset/horizontal offset ratio is 1:1),
showing the vertical offset is equal to the horizontal off-
set and, from south to north, the thrust displacement is
Figure 4. The vertical displacement along the Pengxian-Guanxian fault in Wenchuan Earthquake.
Figure 5. The vertical displacement along the Xiaoyudong fault in Wenchuan Earthquake.
Figure 6. The horizontal displacement along the Xiaoyudong fault in Wenchuan Earthquake.
3.4. Surface Rupture of Leigu Fault
This fault (Figures 1 and 7) belongs to Yingxiu-Beichuan
fault belt and between two parallel northeast striking
faults. The fault’s surface rupture is very complex and it
is also a new fault discovered after the earthquake, show-
ing that it is a transform fault between those two parallel
Yingxiu-Beichuan faults, which has been named Leigu
fault by us.
The fault, striking south-north, extends 3-5 km from
south to north. The surface rupture pattern is stable and
we have confirmed that more than 10 rupture points. Its
southwest block is hanging wall and the northeast block
is foot wall. The largest vertical offset is 2.2 ± 0.5 m and
the largest horizontal offset is 1.9 ± 0.1 m (the average
vertical offset is 1.8 m and the average horizontal offset
is 1.4 m).
In the surface rupture, there are obvious changes from
the north to the south, changing from striking south-north
in the north to striking NWW in the south, which shows
vertical and sinistral horizontal offset in the north (a
channel has been offset vertically 1.9 m and horizontally
1.3 m); and, in the south, the rupture zone shows vertical
and dextral offset (a house foundation has been offset
vertically 1.5 m and 0.5 m and dextral 1.3 m and 0.3 m).
The vertical offset with horizontal offset ratio is 1:1,
showing the thrust displacement is equal to the strike-slip
displacement and, from south to north, the thrust changes
Copyright © 2010 SciRes. IJG
Copyright © 2010 SciRes. IJG
Figure 7. The vertical displacement along the Leigu fault in Wenchuan Earthquake.
bigger. It was noticed that in the north, the fault is sinis-
tral strike-slip and, in the south, it appears to be a dextral
3.5. The landform of Surface Rupture
According to our field observation of the surface rupture,
it had various forms, mainly showing as ridge offsets,
alluvial fan offsets, terrace offset, slopes offsets, channel
offsets, path offsets, highway offsets, cement road over-
lays, structural fractures, sag ponds, ground cracks, ear-
thquake domes, pressure ridge and other types, of which
road scarps are easy to identify.
In Yingxiu region, the surface rupture are showed in
structural cracks and road deformation (asymmetrical
fold ridge) and graben; in Shengxigou and Gaoyuan, the
surface are showed road scarps, road deformation and
pressure ridge; in Bajiaomiao, the surface rupture are
showed in fault scarps. The width of surface rupture is
different along the fault, but on the whole, it is generally
less than 20 meters. Strong deformation is distributed in
the hanging block of the thrust fault and the foot block
has no obvious deformation, or only has deformation in
the vicinity of the fault.
3.6. Dip of Surface Rupture
The Yingxiu-Beichuan fault’s surface ruptures are gen-
erally steep scrapes; the northwest block is hanging wall
and southeast block is foot wall, indicating that the frac-
ture plane should trend northwest. But the plane is diffi-
cult to be discovered; in Bajiaomiao, Hongkou, the plane
was directly exposed at the surface. It tends to northwest
with dip angle 80°-86° and its hanging wall is composed
of upper Triassic Xujiahe coal-bearing strata and its foot
block is loose gravels. The scratches can be distinct in
the plane, indicating high-angle thrust characteristics. As
a result, in the Yingxiu-Beichuan fault, the northwest
tending fault in high-angle should be representative.
However, in Gaoyuan, Hongkou, Yingxiu-Beichuan
fault’s rupture surface trend to southeast. The plane here
is also showed as a very steep scrapes, but the northwest
block is foot side and southeast is hanging side, which
indicates that the plane should trend to northwest. As a
result, we think that Yingxiu-Beichuan fault’s surface
rupture should be northwest trending high-angle surface,
but in some areas, the tendency could be reversed from
northwest to southeast.
The Wenchuan earthquake’s focal mechanisms soluti-
on reveals that the dip angle of plane is only 33°-39° [17].
It is obvious that the surface crack plane is different from
one calculated by focal mechanisms solution: the dip
angle is gentle when deeper. This characteristic is also
similar to an imbricate thrust fault’s structural features.
3.7. Surface Rupture and Shortening Rate
Although in the Yingxiu-Beichuan fault there are differ-
ent structural shortening forms, including road offset and
road overlay, the proper measurement position of surface
deformation is less. In a cement road in Gaoyuan, we
measured the pressure ridge and the thrust overlay, sho-
wing a clear structural shortening phenomenon. In the
cement road, we measured surface deformation in detail,
indicating that the structural shortening rate of this sec-
tion is 7.61 percent and that the biggest structural short-
ening rate of the pressure ridge is 28.6 percent.
The Longmen Shan is the most typical klippe zone in
China; it has a structural shortening rate of 42-43% [1,3-
8]. The result is 7.61%-28.6% in Gaoyuan, showing the
clear structural shortening rate in Wenchuan Earthquake.
3.8. Rupture Process of Wenchuan Earthquake
Although the surface rupture in Bajiaomiao is also steep
scarp as the main form; its hangling wall is Upper Trias-
sic Xujiahe coal-bearing strata and its foot wall is loose
gravel. But the scrape marks have preserved the evidence
for the process analysis of Wenchuan earthquake.
The scrapes plane strikes to N60°E, trending to N300°W
with a dip angle of 85°. We discovered two scratches in
the plane. The first one is nearly vertical, mainly distrib-
uting in upper and lower parts of the plane, while the
second one is nearly horizontal, mainly locating in the
lower part of the plane.
In the plane of the scrapes, we can observe three kinds
of cross cutting relationships between nearly vertical and
horizontal scratches: a nearly vertical one cutting the
nearly horizontal one, a nearly horizontal one cutting the
nearly vertical one and a nearly vertical one in the top
gradually changing to the nearly horizontal one in the
In view of the Upper Triassic Xujiahe coal-bearing
strata in the hanging block and the loose gravel in the
foot block, the scratch preserved in the hangling wall
bedrock should be the evidence of foot wall loose gravel
in the movement process. As a result, the upper marks
preserved in the hangling wall should be the early evi-
dence of the rupture process of the earthquake and the
lower marks preserved in the hanging wall should be the
late evidence of the rupture process.
For this reason, we speculate that the nearly vertical
scratches in the top recorded the thrust movement early,
while the scratches in the bottom recorded the strike-slip
movement lately. According to these three different kin-
ds of cross cutting relationship of scratches, we think that
the late movement is oblique.
According to the focal mechanisms solution, Chen [17]
thought that the Wenchuan earthquake can be divided
into 7 stages, and that, in the beginning stages, the move-
ment showed thrust and then gradually shifted to strike-
slip movement lately. Yuji Yagi [18] has a similar view-
point on the movement process of the devastating earth-
quake which includes two phases: the first phase (0-
50 seconds) with 6.4 m thrust and the second phase (60-
120 seconds) with 4.6 m strike-slip.
As a result, the scratches of the surface rupture reveal
the process confirmed by the focal mechanism solution,
which is that the thrust movement occurred early and the
strike-slip movement occurred lately.
4. Discussion on Kinematic of Active
Tectonics in Longmen Shan and
Wenchuan Earthquake
Indo-Asia collision is the most important events in Ce-
nozoic, which results in the uplift, deformation and
thickening of Qinghai-Tibetan Plateau. The event and its
impact to Cenozoic geological structure has been noticed
and discussed by geoscientists. Two well-known hy-
potheses have been presented; one is a crustal thickening
model [19] and the other one is a lateral extrusion mode
[20].The former emphasizes on north-south crustal shor-
tening and thickening, and the later emphasizes the
east-extrusion along main faults. In the eastern margin of
the Qinghai-Tibetan Plateau, there are two corresponding
pattens which are: Avouac and Tapponnier [20] eastward
thrusting mode, and England et al.’s dextral strike-slip
However, the active tectonics and Wenchuan earth-
quake show the Longmen Shan fault is characterize by
thrust and dextral strike-slip movement, which does not
coincide with England and Molnar’s large scale dextral
shear movement in the eastern margin of Qinghai-Ti-
betan Plateau, and which also does not coincide with
Avouac and Tapponnier [20] eastward thrusting mode in
the eastern margin of the Qinghai-Tibetan Plateau. The
performance of Longmen Shan fault zone has its uni-
queness, which can not be explained in one single mode.
According to the direction of surface movement sho-
wed by GPS measurements [21,22], the northeast corner
of Qinghai-Tibetan Plateau consisting of Longmen Shan
fault and Kunlun Shan fault has the characteristics of
northeastward (Qingling direction) extruding out, which
means that when the Songpan-Ganzi block in eastern
Qinghai-Tibet moved to the east, because of the blocking
of Yangtze platform, it was forced to move to Qinling
Mountains in the northeast and resulted in the characters
with thrust and dextral strike-slip movement mode in
Longmen Shan. The West Qinling fault is thrust with
sinistral strike-slip movement and the blocks between
Longriba fault and east Kunlun fault is also northeastern
extruding out (Figure 8).
5. Discussing of Dynamics Mechanism of
Active Tectonics in Longmen Shan and
Wenchuan Earthquake
According to GPS measurements, India plate is moving
to the north in 50 mm a-1, and different blocks in the
eastern margin of Qinghai-Tibetan Plateau have signifi-
cantly different movement rates. The Songpan-Ganzi
block in the south has a faster horizontal movement rate
than the Songpan-Ganzi block in the north. Active tec-
tonics research [3-8,12,15] shows that the horizontal
movement rate in Longmen Shan is small (1-3 mm a-1),
so is its uplift rate (0.35-0.40 mm a-1) [1]. Its move-
ment mode is characterized by thrust with dextral
strike-slip. But Longmen Shan is the steepest mountain
around Qinghai-Tibetan Plateau, in the range of more than
30 kilometers, it uplifts from 700 meters above sea level to
more than 5000 meters. The small surface slipping rate
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Copyright © 2010 SciRes. IJG
Wenchuan Earthquake coincide with the depth of his-
torical strong earthquake and all of them are shallow
earthquakes, which coincide with the depth of 20 km in
low-velocity layer and also coincide with the uplift depth
of the top of lower crust [9-11].
As a result, in the process of Qinghai-Tibetan Plate-
au’s movement to the east, blocked by the basement of
the Sichuan Basin, the lithosphere is not synchronized as
a whole flow to the east and the flow velocity is different
in different layers. This results in lower crust material in
the Longmen Shan moving as nearly-vertical extrusion
and uplift [23], resulting in the surface rate of tectonic
movement differing according to depth rate as well as the
occurrence of large shallow Wenchuan earthquake (Fig-
ure 9).
Figure 8. Surface movement, epicenter and tectonic frame-
work in Eastern Qinghai-Tibetan plateau.
does not only coincide with the high and steep mountain,
but also does not coincide with the fact of the strong
earthquake of Ms 8.0. As a result, in the Songpan-Ganzi
block and Longmen Shan in the northeast margin of
Qinghai-Tibetan Plateau, the rate of surface movement
does not coincide with the deep tectonic movement rate.
The deep structural process must be thought about in the
seismic hazard assessment.
6. Geological Hazard Caused by Wenchuan
The Wenchuan Earthquake is the most destructive in
intensity and the vastest of affected area in China since
1949. The area of the heavily destroyed region is more
than 100,000 km2. It has the most serious casualties after
the Cicheng Earthquake (Inner Mongolia, 1290), the
Huaxian Earthquake (Shanxi, 1556), the Haiyuan Earth-
quake (Ningxia, 1920) and the Tangshan Earthquakes
(Hebei, 1976).
The Wenchuan earthquake’s focal mechanism solution
shows that Wenchuan Earthquake’s focal depth is 12-19 km,
belonging to shallow earthquake. In addition, we count
the historical earthquake in Longmen Shan as the longi-
tude [3-8,9-11]. The results show that Longmen Shan
tectonic earthquake in lower magnitude was in depth of
5-15 km in advantage and the strong earthquake was in
depth of 15-20 km. Obviously, it is clear that the depth of
The hazards caused by the Wenchuan Ms 8.0 Earth-
quake is known by next main characteristics: 1) seismic
waves have propagated with strong ground motion to
damage construction; 2) surface rupture zone directly
Figure 9. A dynamical model to illustrate possible links between surface processes and upward extrusion of lower crustal flow
channel at the eastern margin of the Tibetan plateau.
Copyright © 2010 SciRes. IJG
destroyed and tear construction along Yingxiu- Beichuan
fault for 220 km and Pengxian-Guanxian fault for 40-
50 km; 3) collapse, landslide and other geological haz-
ards caused by strong vibration of ground motion de-
stroyed buildings. Because the earthquake occurred in
the valleys of the Longmen Shan, especially in Yingxiu-
Beichuan fault, there have been large-scale collapse,
landslides and other geological hazards in Longmen
Shan region. Those hazards have buried or destroyed a
large amount of buildings, for example, half of the
buildings in Chenjiaba, have directly been destroyed by
landslides and a large number of barrier lakes have flood
buildings and have given potential secondary flood threat
to the basin.
According to the earthquake data collected by survey
teams of Gansu, Shanxi and Chongqing seismological
bureaus, InSAR imaging and seismography records, we
studied some important regions with high seismic inten-
sity and have drawn an isoline map of Wenchuan Earth-
quake and distinct the intensities in this region (Figure
10). District is located in Yingxiu-Hongkou, and
Leigu-Beichuan, which are distribute along Yingxiu-
Beichuan fault zone’s hanging wall with a total area of
about 680 km2. Construction in this region almost com-
pletely collapsed, especially in Yingxiu town and Beic-
huan town. Large-scale surface rupture can be followed.
A number of large-scale collapses and landslides blocked
rivers to form barrier lakes, such as the Qingping and
Tangjiashan barrier lakes. District starts from south-
west Yingxiu and end in Shikanzi, Nanba in the north-
east, including Yingxiu-Beichuan surface rupture in a
narrow belt with the long axis N50°E and an area of
about 2520 km2. In this region, most construction col-
lapsed and landslides are common.
To summarize, District and above this of the Wen-
chuan Earthquake affected the area of about 333000 km2.
The isoline map (Figure 10) has the following charac-
teristics: 1) high-seismic intensity lines, especially in
district , distributed along the Longmen Shan in
N40-50°E direction and the long/short axis ratio are
8:1-10:1. District degrees are distributed in three iso-
lated areas with the typical characteristics of multi-point
instant cracks. 2) According to the results of seismic in-
version, the earthquake rupture tear from the vicinity of
Yingxiu to the northeast with characteristics of a one-
direction rupture process. Isoseismal lines also show the
direction of disappearing rapidly to the southwest and
slowly to the northeast with the characteristics of the
Figure 10. Isoseismal line of Wenchuan M8.0 earthquake on 12 May, 2008.
Copyright © 2010 SciRes. IJG
mode. 3) District disappear to Hongyuan and Ruoer-
gai slower than to the Basin, which may be related to that
the Sichuan Basin with relative rigidity Yangtze plate is
not easy for seismic wave absorbing as well as the soft
soil in Hongyuan and Ruoergai enlarge the damage. 4)
District , and in the area ⅥⅦ Ⅷof north Sichuan,
Gansu and Shanxi are gradually turning to east-west di-
rection and this may be the result of controlling of the
regional faults.
7. Preliminary Conclusions
In this paper, based on the Longmen Shan seismic zone’s
geological background, tectonic setting, stratigraphy and
lithology, we have summarized the Longmen Shan sur-
face rupture and progress and explore the tectonic kine-
matics and dynamics of Wenchuan Earthquake. Accord-
ing to the geological disasters caused by Wenchuan
Earthquake, we have made several suggestions for re-
construction in the affected areas.
According to historical records and active tectonics,
we believe that the Longmen Shan fault zone is a dan-
gerous earthquake zone and the three main faults have
the ability to induce earthquakes > Ms 7. The Yingxiu-
Beichuan fault is the most important earthquake-induc-
ing fault; the interval should be at least about 1000 a. It
belongs to the low-frequency seismic activity zone, but it
has a potential risk to induce a strong earthquake with
characteristics of thrust and dextral strike-slip move-
By comparing the initial analysis of Wenchuan Earth-
quake and historical earthquakes records, we believe that,
the May 12, 2008 Wenchuan Earthquake belongs to
thrust and strike-slip type earthquake. According to
north-south striking fault (Xiaoyudong, Leigu and Deng-
jiaba faults) and surface offsets, Yingxiu-Beichuan fault
surface rupture zone is divided into two zones of high-
value and low-value. According to scratches on the scr-
aps in Hongkou, the earthquake rupture process is di-
vided into two phases: early thrust and lately-inclined
strike-slip movement. As a result, in the earthquake rup-
tured zone, there are two components of thrust and
strike-slip, thrust displacement is slightly larger than
dextral strike-slip one. This does not coincide with the
crustal thickening mode and the lateral extrusion mode,
which means that Yingxiu-Beichuan fault is special one
and can not be explained by one single model. In view of
the surface moving rate of Longmen Shan does not coin-
cide with its moving rate in the depth, we discussed the
dynamic geological model between surface process and
lower crust flow and think that the vertical pressure and
vertical movement of lower crustal materials in Longmen
Shan results in the eastern thrust movement, uplift of
Longmen Shan tectonic belt and Wenchuan Earthquake
as well.
8. Acknowledgements
We are very grateful to the people who provided us sup-
ports and help. Finally, we thank the people of the Long-
men Shan region for their unending curiosity, hospitality,
and generosity.
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