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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 116, B02405, doi:10.1029/2010JB007821, 2011
Slip rates and seismic moment deficits on major active faults
in mainland China
Hui Wang,1,2 Mian Liu,2 Jianling Cao,1 Xuhui Shen,1 and Guomin Zhang1
Received 2 July 2010; revised 5 November 2010; accepted 6 December 2010; published 8 February 2011.
[1] The Chinese mainland features widespread active faults and intensive seismic activity;
both can be described in terms of slip rates on these faults. Previous studies of fault slip
rates in mainland China have focused on individual faults or fault segments, and large
discrepancies exist among results derived from different methods. Here we derive a
self‐consistent estimate of the slip rates on all major faults in mainland China using
the recently updated GPS data and an elastic block model. The predicted slip rates are high
in western and low in eastern China, ranging from 25.1 ± 2.0 mm/yr in the Himalayan
Thrust System to less than 1.0 mm/yr in north China. Using these slip rates, we estimated
the rates of moment accumulation on the major fault zones and compared them with the
seismic moment released on each fault zone using the Chinese historical earthquake catalog
that extends for more than 2000 years in many regions. The results show nine seismic
zones with large moment deficits (unreleased moment). Future refinement of GPS
measurements and earthquake history will allow better estimates of slip rates on individual
faults and better assessment of earthquake hazard on these faults in mainland China.
Citation: Wang, H., M. Liu, J. Cao, X. Shen, and G. Zhang (2011), Slip rates and seismic moment deficits on major active faults
in mainland China, J. Geophys. Res., 116, B02405, doi:10.1029/2010JB007821.
1. Introduction
[2] China is a country of active tectonics with high seismic hazard (Figure 1). Devastating earthquakes include the
1556 Huaxian earthquake (M 8.0), the deadliest earthquake
in human history with 830,000 people perished [Division of
Earthquake Monitoring and Prediction, State Seismological
Bureau, 1995], and the 1976 Tangshan earthquake (M 7.8)
that destroyed the industrial city of Tangshan and killed
∼250,000 people. In 2008, the great Wenchuan earthquake
(Mw 7.9) killed more than 80,000 people and injured
thousands, and 2 years later, on 14 April 2010, an Mw 6.9
earthquake in the Tibetan Plateau took nearly 3000 people’s
lives and collapsed more than 15,000 houses.
[3] Assessing earthquake hazard in China is particularly
challenging, because most of these earthquakes occur on a
complex network of faults in the interior of the Eurasian plate
(Figure 1). In the past decade extensive GPS measurements
have been conducted in mainland China (Figure 2). The GPS
results help to identify fast moving faults and deforming
regions, but these results do not directly relate to seismic
hazard. The 2008 Wenchuan earthquake, for example,
occurred on the Longmen Shan fault zone where the slip rate
is <3 mm/yr [Gan et al., 2007; Shen et al., 2005; Zhang et al.,
2004].
1
Institute of Earthquake Science, China Earthquake Administration,
Beijing, China.
2
Department of Geological Sciences, University of Missouri, Columbia,
Missouri, USA.
Copyright 2011 by the American Geophysical Union.
0148‐0227/11/2010JB007821
[4] Nonetheless, slip rates are a basic indicator of the rates
of strain energy accumulation on faults. When compared
with moment release by previous earthquakes, the deficit
(unreleased moment) or surplus (over‐released moment) can
provide some useful insight into the potential earthquake
hazard on a given fault [Meade and Hager, 2005a]. Doing
so requires a long and, ideally, a complete record of previous earthquakes, which is unavailable in most places. In
China the problem is less because of its long historic record
of earthquakes that extends for more than 2000 years in
many regions [Division of Earthquake Monitoring and
Prediction, State Seismological Bureau, 1995].
[5] Although slip rates have been studied for many faults
in mainland China, results from different methods often give
large discrepancies [Cowgill, 2007; Cowgill et al., 2009;
Meade, 2007; Meriaux et al., 2005, 2004; Tapponnier et al.,
1990; Zhang et al., 2007]. Most studies have also focused
on individual faults or fault segments. In this study we
derive self‐consistent slip rates on all major faults in
mainland China using the recently updated GPS data [Zhang
and Gan, 2008] in a continental‐scale elastic block model.
We then use these slip rates to estimate the rates of moment
accumulation on these faults and compare them with seismic
moment release.
2. Active Faults in Mainland China
[6] The active fault systems in western China are predominantly E‐W oriented strike‐slip and thrust faults
(Figure 3), reflecting the long history of terrane accretion to
the southern margin of the Eurasian plate [Yin and Harrison,
2000] and the continued collision between the Indian and
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Figure 1. Map of mainland China showing major active faults (thin lines) and seismicity (dots). Blue
dots indicate epicenters of historic earthquakes before 1900; red dots indicate earthquakes during
1900–2010 (mostly instrumental records). The barbed lines represent plate boundary faults [after Bird,
2003].
Asian continents in the past 50–70 Ma [Molnar and
Tapponnier, 1975; Tapponnier and Molnar, 1977;
Tapponnier et al., 1982, 2001; Yin and Harrison, 2000].
From the Himalayan Thrust System northward, the major
faults in the Tibetan Plateau include the Karakorum‐Jiali
fault, the Xianshuihe fault, the Kunlun fault, the Altyn Tagh
fault, and the Qilian Shan‐Haiyuan fault; the last two bound
the northern margin of the Tibetan Plateau. The compressive
faulting goes all the way to the Tian Shan and the Altai
mountains, showing the far‐field impact of the Indo‐Asian
collision [Tapponnier and Molnar, 1979; Yin et al., 1998].
[7] The eastern margin of the Tibetan Plateau is bounded
by the Longmen Shan fault and the Anninghe‐Xiaojiang
fault. Together with the faults bounding the western side of
the Ordos block (Figure 3), these faults form the so‐called
south‐north seismic belt in Chinese literature. This belt,
roughly following the 105°E longitude, also separates the
collision‐controlled western China from eastern China. The
latter consists of the south China and the north China blocks,
which are two cratons that collided since early Mesozoic
along the Qinling‐Dabie fault belt [Kusky et al., 2007;
Yin and Nie, 1996]. Active faults in eastern China reflect
both the influence from this collision and the effect of late
Mesozoic to early Cenozoic convergence between the
Eurasian and Pacific plates, as witnessed by the system of
NE‐SW oriented faults (Figure 3).
[8] These faults divide mainland China into a hierarchy of
crustal blocks or subplates [Bird, 2003; Geological Institute,
China Academy of Sciences, 1974; Ma, 1989]. The first‐
order blocks include the Tibetan Plateau, the Tarim basin,
the northeast China (Dongbei), the south China, and the
north China (Figure 3). The North China block can be further divided into the Ordos block, the North China Plain,
and the coastal regions [Liu et al., 2007]. Active faulting,
differential crustal motion, and earthquake activity have
been used to further delineate active tectonic blocks
[Thatcher, 2007; Zhang et al., 2003]. Most crustal deformation and earthquakes are concentrated along the boundaries of these blocks, whose internal deformation is
relatively coherent. Some of the blocks are rigid with little
internal deformation, such as the Tarim, the Ordos, and the
south China blocks.
3. The Elastic Block Model and GPS Constraints
[9] Fault slip rate is a primary indicator of active tectonics
and seismic activity. In this section we briefly describe the
elastic model and the GPS data we used to derive a self‐
consistent estimate of fault slip rates on all major active
faults in mainland China.
3.1. The Elastic Block Model
[10] The GPS data (Figure 2) can be used to derive fault
slip rate on the major faults. Most GPS site velocities,
measured over a period of a few years, reflect mainly the
interseismic crustal strain rate. Although faults are locked
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Figure 2. GPS site velocities in mainland China relative to stable Eurasia [after Zhang and Gan, 2008],
plotted on the topographic map. Error ellipses represent the 95% confidence level. The red arrows are
outliers. See text for details.
between ruptures, the slip rate on the fault can be estimated
from the GPS velocities across the fault. For a single fault,
this can be done using a one‐dimensional elastic dislocation
model [Savage and Burford, 1973]. For an infinitely long
strike‐slip fault, the station velocity, v, along a profile perpendicular to the fault is related to the slip rate (b), fault
locking depth (D) and distance from the fault (x):
v ¼ ðb=Þ arctanð x=DÞ
ð1Þ
For a network of faults, Meade et al. [2002] and Meade and
Hager [2005b] have developed a three‐dimensional elastic
block model to derive self‐consistent slip rates on all faults.
The slip rates so derived are the total slip rates, which
include both the interseismic and coseismic slips. In the
model, the interseismic velocity (VI) is assumed to be the
difference between block velocity (the total slip rate, VB)
and the yearly coseismic slip deficit velocity (VCSD):
~
vI ¼ ~
xS Þ ~
xS ;~
vB ð~
vCSD ð~
xF Þ
ð2Þ
where ~
xS is the station coordinate and ~
xF represents the fault
geometry. The block velocity is established using the rotation about an Euler pole W:
~
vB ð~
xS Þ ¼ W ~
xS
ð3Þ
The yearly coseismic slip deficit velocity (VCSD) is calculated using the elastic dislocation model [Okada, 1992]. The
predicted interseismic velocity at a point is equal to the sum
of the block rotation rate and the integrated effects of elastic
strain accumulation from all faults. The predicted slip rates
meet the condition of internal consistency that any closed
path integral of velocity sums to zero [Meade et al., 2002].
[11] We use this approach to construct a block model for
mainland China (Figure 4), using the code from Meade and
Hager [2005b]. The division of the blocks follows that of
previous studies, which were based on neotectonics and
geodetic results of crustal motion in mainland China [Chen
et al., 2004; Deng et al., 2002; Gan et al., 2007; Han et al.,
2003; Meade, 2007; Shen et al., 2005; Thatcher, 2007;
Zhang and Gan, 2008; Zhang et al., 2003]. We delineated
the block boundaries based on traces of the major faults,
simplifying complex fault zones as linear boundaries. In
north China where the traces of some major active fault are
not clear, the boundaries are based on geophysical data and
earthquake activity [Han et al., 2003]. These blocks are
listed in Table 1.
[12] All faults are assumed to be vertical except the
Himalayan Thrust System, which dips ∼10° northward
[Meade, 2007]. This simplification has two reasons. One
reason is the uncertainty of the geometry of most faults at
depth. The other is that most GPS sites are far from the
faults, hence the predicted velocities at these sites are not
sensitive to the detailed fault geometry at depth. Similar
simplification has been used in previous studies [McCaffrey,
2005; Meade, 2007; Meade and Hager, 2005b]. With fault
planes simplified to be vertical, the dip‐slip motion (compressive or extensional) on such a fault is represented by
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Figure 3. Topography, major active faults, and tectonic units in mainland China. Dashed lines indicate
hidden faults from the interpretation of satellite images. Data of faults are from Deng et al. [2002].
Figure 4. The block model for mainland China. Names of the blocks are listed in Table 1. The thin lines
are active faults described in Figure 3. Barbed lines are plate boundaries.
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Table 1. Crustal Blocks in Mainland China and Their Euler Vectors
No.a
Blocks
Longitude (deg)
Latitude (deg)
Angular Velocityb (rad/Myr)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
East Lhasa
Himalayan
Lhasa
Eastern Tibet
Qiangtang
Karakorum
Southwest Yunnan
South Yunnan
West Sichuan
East Yunnan
Songpan‐Ganze
Qaidam
Hexi
Qilian
Gansu
Alaxan
Tarim
Tian Shan
Jungar
South China
Ordos
Taihang
Huaihe
East Sea
North China Plain
Yan Shan
96.329 ± 0.657
115.344 ± 25.748
74.121 ± 1.867
95.563 ± 0.224
104.639 ± 5.392
92.541 ± 8.061
104.611 ± 2.306
118.289 ± 6.718
93.735 ± 1.027
93.837 ± 1.315
100.884 ± 0.253
151.686 ± 54.031
79.221 ± 34.230
106.957 ± 6.506
103.538 ± 0.184
98.619 ± 3.964
98.348 ± 0.686
97.578 ± 3.585
71.415 ± 3.522
221.426 ± 14.748
121.669 ± 3.079
132.494 ± 10.631
175.979 ± 23.969
130.843 ± 3.379
137.135 ± 24.082
136.727 ± 15.250
23.279 ± 0.680
16.971 ± 16.188
31.744 ± 0.417
25.246 ± 0.417
−1.04 ± 16.710
36.869 ± 0.746
19.879 ± 1.689
24.05 ± 0.785
23.557 ± 0.967
22.215 ± 0.655
26.139 ± 0.842
−42.78 ± 44.947
77.854 ± 17.970
16.448 ± 17.388
30.5 ± 0.595
10.371 ± 23.633
37.843 ± 0.263
37.236 ± 1.826
48.159 ± 0.803
56.949 ± 5.429
48.173 ± 2.005
53.667 ± 6.117
63.802 ± 8.543
45.455 ± 2.829
55.874 ± 14.011
56.231 ± 7.652
−1.47 ± 0.15
−0.22 ± 0.15
1.51 ± 0.39
−1.85 ± 0.13
−0.34 ± 0.14
−0.93 ± 0.54
0.60 ± 0.24
0.42 ± 0.15
−1.27 ± 0.20
−0.96 ± 0.16
−1.02 ± 0.13
−0.10 ± 0.01
0.03 ± 0.21
−0.20 ± 0.15
−0.97 ± 0.11
−0.07 ± 0.05
−0.56 ± 0.03
−0.32 ± 0.08
0.28 ± 0.06
−0.07 ± 0.003
0.20 ± 0.04
0.14 ± 0.06
0.08 ± 0.06
0.22 ± 0.05
0.13 ± 0.10
0.08 ± 0.04
a
Events are the same as in Figure 3.
Positive for counterclockwise rotation and negative for clockwise rotation.
b
horizontal convergence toward, or divergence from, the
block boundaries, respectively.
[13] Because Okada’s solutions [Okada, 1992] are for
surface deformation in a homogeneous elastic half‐space, to
use this approach in our large‐scale model we need to
project the fault geometry and station position from spherical to planar geometry. We use a locally tangent oblique
Mercator projection to flatten the spherical geometry. In
such a way, the trace of a fault segment is approximated as a
great circle path between its two endpoints. The spatial
distortion due to the projection is < 2%, and the far‐field
velocities produced by the fault dislocation are insignificant
[Meade and Hager, 2005b].
3.2. The GPS Constraints
[14] The GPS data used in our study are from a recently
updated compilation by Zhang and Gan [2008], which is
mainly based on results from the Crustal Motion Observation Network of China (CMONC). CMONC consists of 25
continuous stations, 56 annually surveyed stations, and
nearly one thousand survey mode stations. The data were
collected between 1998 and 2004; measurements at each site
were for at least 72 h. In addition, Zhang and Gan [2008]
combined other data sets to increase the coverage and station density in Mongolia, India, Himalayan, and central
Tibet.
[15] The GPS data include some outliers of various nontectonic sources. These outliers are usually of large measurement errors and not coherent with other nearby
observations. In our block model, we used both the complete GPS data set and a reduced data set with the outliers
removed. We removed the outliers using the F test. First, we
use all the GPS site velocities in the block model to calculate
site velocities, and evaluate the RMS c2n (c2n = rTC−1r),
where n is the number of GPS sites in the model, r is the
vector of residual velocities and C is the data covariance
matrix. Next, we remove the site with the largest RMS
residual, and use the rest of the GPS data to predict the site
2
. Finally,
velocities again and then evaluate the RMS cn−1
we use the F test to evaluate the significance of the outlier.
The F value is defined as
F ¼ F 2n ; 2n 3; 2n1 ; 2n 5 ¼
2n
2
= n1
2n 3 2n 5
ð4Þ
Then the probability P(F) is evaluated. The site is removed
if the F test exceeds 90% confidence, and the procedure
repeats until the F test yields <90% confidence. The reduced
GPS data set has 1162 GPS site (91.8% of total sites)
velocities. The mean uncertainties of this reduced GPS data
set are 1.67 mm/yr in the east‐west direction and 1.63 mm/yr
in the south‐north direction, respectively (Figure 2). The
results in section 4 are from this reduced data set, and the
impact of removing the outliers is discussed in section 6.2.
4. Model Results
4.1. Locking Depths of Major Faults and the Site
Velocities
[16] The depth to which the faults stay locked between
ruptures affects the distribution of strain rates on the surface,
as shown in equation (1). A deeper locking depth would
cause broader strain distribution, and vice versa. The locking depths can be constrained in the block model by fitting
to the GPS data. Figure 5 shows how the fits vary with the
locking depth in various regions. The optimal locking depth
is obtained at the minimum of RMS c2. First, we determine
a uniform locking depth for all faults and use it as the initial
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Figure 5. Optimal fault locking depths for mainland China and its various regions. The red lines show
the percent increase in velocity misfit relative to the best fitting model. Black lines show the rate of
moment accumulation for each region as a function of the locking depths of faults. The gray shaded bands
show the uncertainties due to errors of slip rates. The light red bands indicate the range of locking depth
where change in c2 is significant to 90%. (a) Mainland China; (b) Tibetan Plateau; (c) Xinjiang region;
(d) north China.
value in our block model (Figure 5a). The best fit is about
19 km. Using this initial value, we then determined the
optimal locking depth of faults in the Tibetan Plateau (21 km),
the Xinjiang region (9 km), and north China (>40 km). In
north China, the variation of c2 for a range of locking depths
(0–40 km) is less than 2% (Figure 5d), indicating that
the GPS data cannot well constrain the locking depths. The
reason is that many GPS site velocities in north China have
errors larger than their velocity components (Figure 2).
[17] Additional constraints of fault locking depth are
provided by earthquake focal depths. Zhang et al. [2002]
have shown that the mean earthquake focal depth is 16 ±
7 km in Chinese continent. The focal depths of most events
(90% of all events) are 5–24 km in eastern China and are 5–
34 km in western China. The mean earthquake focal depth is
13 ± 6 km in eastern China, and 18 ± 8 km in western China.
Relocation of major earthquakes in the Tibetan Plateau
indicates the focal depths of most events to be shallower
than 25 km [Yang et al., 2005]. Hence, the locking depths
indicated by focal depths are generally consistent with those
estimated from the block model except in north China. We
use 10 km as the locking depth of faults in north China,
according to the focal depths of major earthquakes and the
estimated depths of the seismogenic layer in this region [Zhu
et al., 2005].
[18] Using the optimal locking depths for the major faults,
we predicted site velocities using the block model. The results
are in good agreement with the GPS velocities (Figure 6).
The mean residual velocity is 0.91 mm/yr, less than the
mean uncertainty of the GPS data with 90% confidence.
About 69% of the residual velocity components are smaller
than 1.0 mm/yr. The large misfits are mainly found around
southern and western Tibet, where the GPS sites are sparse
and the observational errors are relative large (Figure 2).
4.2. Block Rotation
[19] Figure 7 shows the predicted rotation of crustal
blocks in the Chinese mainland; their Euler poles and
rotation rates are listed in Table 1. The largest rotation occurs
around the Tibetan Plateau. In general, more rotation is
found in western China than in eastern China.
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Figure 6. Residual velocities (the difference between the predicted and the GPS site velocities). The
mean RMS is 0.91 mm/yr. Inset is the histogram of residuals that shows good agreement between the
predicted and the GPS velocities.
Figure 7. Predicted rigid rotation of the blocks. The fans in gray show predicted block rotations of each
block; the small fans show 2s uncertainties.
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Figure 8. Predicted fault slip rates along major active faults. (a) Strike‐slip rates. (b) Dip‐slip rates
shown as contraction/extension rates because most faults are simplified as being vertical. Thickness of
lines is proportional to the rates (scales are shown in the inset).
[20] The Tarim, the Ordos, and the South China blocks are
relatively rigid blocks, so we compare their rotations from
our model with those from previous regional‐scale studies.
For the Tarim block, our predicted Euler pole (98.3° ± 0.7°E
and 37.8° ± 0.3°N) is similar to that found by Shen et al.
[2001] (96.2° ± 0.8°E and 37.5° ± 0.4°N), who used a
subset (28 GPS site velocities) of the data set used in our
study. These locations are also similar to that found by Li
et al. [2003] (100.5° ± 1.0°E, 37.1° ± 0.3°N). The Ordos
block is shown to rotate around an Euler pole located at
121.7° ± 3.1°E and 48.2° ± 2.0°N in our model, similar to
the location of 133.2° ± 11.3°E and 54.2° ± 4.8°N found
by Li et al. [2003]. The counterclockwise rotation of the
Ordos block is consistent with the eastward crustal extrusion
driven by the Indo‐Asian collision [Xu et al., 1993]. The
South China block rotates clockwise round an Euler pole at
41.4° ± 14.9°E and 56.9° ± 5.4°S, similar to that found by
Zhang and Gan [2008].
[21] The southeastern Tibet in our model consists of
4 blocks (blocks 1, 4, 9, and 10 in Figure 4). These blocks
rotate at similar rates, with their Euler poles clustered within
93°–96°E and 22°–25°N. These results are consistent with
the clockwise rotation around the eastern Himalayan syntax
in the southeastern Tibet [Allmendinger et al., 2007].
4.3. Slip Rates on Major Faults
[22] The main results from our block model are a self‐
consistent estimate of the slip rates on all major faults in
mainland China (Figure 8). The details are listed in Table 2,
together with previous estimates based on geological or
geodetic data. Our predicted slip rates show sharp contrast
between western China (high) and eastern China (low),
roughly separated along 105°E longitude, or the south‐north
seismic belt. We briefly describe the results in three tectonic
regions where the slip rates are the highest: the Tibetan
Plateau, the Xinjiang region, and north China.
4.3.1. Slip Rates in the Tibetan Plateau and Its Vicinity
[23] The highest slip rates are found in the faults within
and around the Tibetan Plateau. From east to west along the
Himalaya Thrust System, the predicted mean contraction
rate changes from 22.0 ± 1.8 mm/yr to 18.3 ± 1.3 mm/yr,
similar with those found by Meade [2007] but higher than
the rates by others [Shen et al., 2000; Wang et al., 2001;
Zhang et al., 2004]. In the eastern part of the Tibetan
Plateau, the Indo‐Eurasian plate boundary is mainly a system of right‐lateral strike‐slip faults. Our model predicts
more than 40 mm/yr right‐lateral strike‐slip motion and 14.6 ±
1.1 mm/yr convergence on this part of the plate boundary.
These results are higher than previous estimates [Bertrand
et al., 1998; Maurin et al., 2010; Vigny et al., 2003].
[24] Within the Tibetan Plateau, the dextral Karakorum
fault has a strike‐slip rate of 11.6 ± 3.7 mm/yr and a convergence rate up to 4.3 ± 1.6 mm/yr, similar to those estimated from InSAR data [Wright et al., 2004] but smaller
than geological results [Brown et al., 2002; Chevalier et al.,
2005; Valli et al., 2007]. The dextral Red River fault has a
slip rate about 2.4 ± 1.0 mm/yr. The sinistral Xianshuihe‐
Xiaojiang fault has high slip rates ranging from 18.2 ± 0.8 to
10.4 ± 0.4 mm/yr on its various segments. The sinistral east
Kunlun fault has a mean slip rate of 10 mm/yr. Bounding
the Tibetan Plateau to the north is the sinistral Altyn Tagh–
Haiyuan fault zone. The mean slip rate on the Altyn Tagh
fault is 6.9 ± 0.9 mm/yr, generally decreasing eastward.
These rates are generally consistent with those from other
GPS measurements [Shen et al., 2001; Zhang et al., 2004,
2007], but is lower than the 17.8 ± 3.6 mm/yr geological
estimates [Meriaux et al., 2004] (Table 2). The predicted
mean slip rate on the Haiyuan fault is 8.7 ± 0.9 mm/yr.
Bounding the eastern margin of the Tibetan Plateau is the
Longmen Shan fault, where the predicted convergence rate
is 3.2 ± 0.6 mm/yr, and the dextral slip rate is 1.2 ± 0.5 mm/yr.
These low slip rates are similar to previous estimates [Gan
et al., 2007; Shen et al., 2005; Wang et al., 2010; Zhang
et al., 2004].
[25] Consistent with the formation of north trending grabens within the Tibetan Plateau [Blisniuk et al., 2001; Kapp
et al., 2008; Liu and Yang, 2003; Yin, 2000], the model
results show the south‐north trending faults in Tibet to be
extensional, with the extension rates up to 10.7 ± 2.5 mm/yr
(Figure 8b).
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Table 2. Predicted Fault Slip Rates on Major Faults
Previous Resultsc
(mm/yr)
Strike‐Slip
Ratea
(mm/yr)
Contraction/
Extension Rateb
(mm/yr)
Himalaya Thrust
System
∼4.0 ± 2.0
−22.0 ± 1.8 to
−18.3 ± 1.3d
Sagaing
Karakorum
−45.6 ± 1.2
−11.6 ± 3.7
−14.6 ± 1.1
−4.3 ± 1.6
Red River
Xianshuihe
−2.4 ± 1.0
18.2 ± 0.8
−3.1 ± 0.8
3.5 ± 1.0
Xiaojiang
Longmen Shan
10.4 ± 0.4
−1.2 ± 0.5
3.2 ± 0.6
−3.2 ± 0.6
West Kunlun
East Kunlun
0.5 ± 2.0
10.1 ± 1.2
−3.0 ± 2.0
−3.0 ± 1.1
Altyn Tagh
6.9 ± 0.9
−1.5 ± 1.3
Qilian
Haiyuan
−1.3 ± 1.1
8.7 ± 0.9
−6.0 ± 1.1
−2.7 ± 0.5
South Tian Shan
2.8 ± 0.6
−10 to −13(32)
North Tian Shan
Altai
1.1 ± 0.8
−4.9 ± 0.5 to
−7.9 ± 0.7
0.9 ± 0.4
−1.8 ± 0.5
−6.8 ± 0.8 to
−2.9 ± 1.0
−6.3 ± 1.1
−5.4 ± 0.6
−0.4 to −1.9 (27)
4.5 ± 1.0 (27);
5–10 (29);
10 ± 2 (30);
12 ± 4 (31)
<−2(33)
−2 to −12 (32)
−2.6 ± 1.0 to −1.2 (35)
∼−3 (34)
‐
0.8 ± 0.4
−4.6 ± 0.4
<3 (36)
‐
5(37); 7 ± 2 (38)
−1.1 to −3.2 (39)
4 ± 2 (2)
−0.4 (38); 2 (40)
∼1 (35); 1.6 (38)
−2 to −39 (41)
−2.3 ± 0.8 (38);
2.2–6.47 (40)
3.1 (38);
2.6–4.7 (40)
‐
Fault
Qinling‐Dabie
Southeast China
costal zone
Shanxi rift
Weihe rift
Tanlu
Hetao
GPS
Geological
−16 to −24 (1);
−22 ± 2.0 (2);
∼16 (3); 15–20 (4)
∼−20 (1); −20 (6); −18 (7)
−4 to −2 (1); about −7 (9)
−21 ± 5.0 (5)
∼10 (1); 0.6 (13); 2 (14)
∼10 (1); 11.2–15.7 (13);
10–12 (14); ∼14.4 (16)
9.4 (13); 7 (14)
−3 (1); −4.0 ± 2.0 (4);
−1.1 (13);
−4.1 (16); −1.2 to
−3.3 (19)
2(1)
∼10 (1); 12–14 (3); 7.1 (13);
10–12 (14); 13.7 (16)
2.3 ± 1.3–7.2 ± 0.6 (1);
5.0 ± 2.0–6.5 ± 1.6 (4);
7–10 (9); 1.6–15.9 (16);
0 ± 2–10 ± 2 (23)
−2 (16); −5.5 ± 1.8 (4)
8.6 (16)
−0.6 ± 0.5
1.4 ± 0.4
−0.7 ± 0.6
0.6 ± 0.4
0.8
0.5
0.5
0.5
Yinchuan rift
−2.6 ± 0.5
1.0 ± 0.5
‐
Zhangjiakou‐Bohai
1.9 ± 0.4
0.5 ± 0.5
1.8 ± 1.0 (2)
±
±
±
±
0.3
0.3
0.5
0.5
<3 (2)
‐
−10 to −23 (8)
−9 to −17 (10); −1 to
−3 (11); −10 (12)
−1 to −3 (15)
2–28 (15); 10 (17);
15 ± 5 (18)
12∼28 (15)
<−3 (20)
‐
11.5 ± 2 (21); >
10 to <2 (22)
17.8 ± 3.6 (24);
20–34 (25);
14–9 (26)
a
Positive for sinistral motion, and negative for dextral motion.
Positive for extension (normal fault) and negative for contraction (reverse fault). Most faults are assumed to be vertical; for them the positive and
negative values represent horizontal motion toward or away from the faults, respectively. In all cases, the slip rate is the mean value of all segments
of a fault.
c
Numbers in parentheses indicate references: (1) Meade [2007]; (2) Shen et al. [2000]; (3) Wang et al. [2001]; (4) Zhang et al., 2004; (5) Lavé and
Avouac [2000]; (6) Vigny et al. [2003]; (7) Maurin et al. [2010]; (8) Bertrand et al. [1998]; (9) Wright et al. [2004]; (10) Valli et al. [2007]; (11) Brown
et al. [2002]; (12) Chevalier et al. [2005]; (13) Wang et al. [2008]; (14) Shen et al. [2005]; (15) Wang et al. [1998]; (16) Gan et al. [2007]; (17) Molnar
and Deng [1984]; (18) Allen et al. [1991]; (19) Wang et al. [2010]; (20) Densmore et al. [2007]; (21) Van der Woerd et al. [2002]; Van der Woerd et al.
[1998]; Van der Woerd et al. [2000]; (22) Kirby et al. [2007]; (23) Zhang et al. [2007]; (24) Meriaux et al. [2005]; (25) Meriaux et al. [2004]; (26)
Cowgill et al. [2009]; (27) Tapponnier et al. [1990]; (28) Li et al. [2009]; (29) Burchfiel et al. [1991]; (30) Jing et al. [2007]; (31) Lasserre et al. [1999];
(32) Yang et al. [2009]; (33) Brown et al. [1998]; (34) Avouac et al. [1993]; (35) Calais et al. [2003]; (36) Enkelmann et al. [2006]; (37) Peltzer et al.
[1985]; (38) Zhang et al. [1998]; (38) Deng et al. [2002]; (40) Working Group of the Active Fault Zone Around the Ordos, Chinese Seismological
Bureau [1988]; (41) Xu and Deng [1996].
d
When two values are shown, they represent the mean values on two different segments of the fault system.
b
[26] On the Sagaing fault, the predicted slip rates (∼40 mm/
yr) is much higher than the ∼18 mm/yr strike‐slip rate based
on geological data [Bertrand et al., 1998; Maurin et al., 2010;
Vigny et al., 2003]. This may be partially due to the lack of
GPS sites near the fault in our model.
4.3.2. Slip Rates in the Xinjiang Region
[27] The northwestern China, or the Xinjiang region,
stretches from the southern Tarim basin to the Altai
Mountains (Figure 3) and includes blocks 17–19 in Figure 4.
Major faults here include those bounding the northern and
southern sides of the Tian Shan and Altai Mountain ranges.
They are mainly reverse faults with strike‐slip components.
The active compressive deformation in this region witnesses
the far‐field impact of the Indo‐Asian collision [Molnar and
Tapponnier, 1975; Yin et al., 1998].
[28] On the south Tian Shan fault, the mean convergence
rate is 6.8 ± 0.8 mm/yr on the western segments and 2.9 ±
1.0 mm/yr on the eastern segments. Similar trends are found
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Figure 9. Predicted rates of moment accumulation along each fault zone. The rates are proportional to
the thickness of lines (scale is shown in upper right corner). Numbers are in 1017 N m/yr.
for the north Tian Shan fault. The total rate of crustal
shortening across the Tian Shan maintain ranges is nearly
50% of the convergence rate between the Indian and Eurasian plates, consistent with the results of previous results
[Abdrakhmatov et al., 1996; Molnar and Ghose, 2000;
Thompson et al., 2002; Wang et al., 2000; Yang et al.,
2009].
[29] The predicted slip rate on the right‐lateral Altai fault
is about 4.9–7.9 mm/yr, similar to the results of Calais et al.
[2003]. Our model also predicts 4.4–6.4 mm/yr convergence
on the Altai fault, confirming that the Indo‐Asian collision
affected at least this far north [Molnar and Tapponnier,
1975].
4.3.3. Slip Rates in North China
[30] The North China block has many large historic
earthquakes and some damaging earthquakes in the past
century (Figure 1), including the 1976 Tangshan earthquake
(M = 7.8). It is bounded by the Zhangjiakou‐Bohai fault
zone to the north and the Qinling‐Dabie fault system to the
south (Figure 3). From west to east, the North China block
consists of the relatively rigid Ordos Plateau, the North
China Plain, and the coastal regions. The Ordos Plateau is
bounded by rift zones, and the North China Plain has a
system of ENE and WNW oriented faults (Figure 3). The
predicted slip rates on the faults in north China are generally
less than 3.0 mm/yr (Figure 8). For example, the Shanxi
rift is shown to have a right‐lateral strike‐slip rate of 0.6 ±
0.5 mm/yr and extension rate of 0.8 ± 0.3 mm/yr. These
results are comparable with previous geodetic estimates but
lower than the 2–4 mm/yr extension rates from geological
estimates (Table 2). Some of this discrepancy may be due
to the timescale‐dependent fault behavior [He et al., 2003].
The relatively low fault slip rates are consistent with the
lower seismicity in north China in comparison with that in
western China.
5. Moment Balance
[31] The predicted slip rates on major active faults provide
useful insight into active tectonics in mainland China; when
combined with earthquake history on the faults, they may
also contribute to a better understanding of earthquake
hazard. Here we use the predicted slip rates to estimate the
rate of moment accumulation on the major active faults in
mainland China, and compare the results with seismic
moment release to identify faults of large moment deficit
(unreleased moment).
5.1. Rates of Moment Accumulation
[32] The rates of scalar moments (M_ o) accumulation
P on a
m∣s∣A,
given fault segment can be estimated as M_ o =
where ∣s∣ is the magnitude of the total slip rate, which includes both strike‐slip and dip‐slip (contraction/extension
for vertical faults) rates on the fault segment, A is the area
of locked fault plane, and m is the shear modulus.
Assuming m = 30 GPa and using the optimal locking depths
(Figure 5), we found that the rate of moment accumulation is
185 ± 34 × 1018 N m/yr for the entire Chinese mainland (the
uncertainties are based on those of the predicted fault slip
rate). It is equivalent to the moment release by an Mw 7.4
earthquake per year.
[33] Moment accumulation is the fastest in the Tibetan
Plateau (Figure 9), consistent with the intense seismicity
there (Figure 1). The total moment accumulation in the
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Table 3. Slip Rates and Moment Balance on Major Seismic Belts
Rate of Moment Accumulation
No.a
Seismic Belt
Slip Rateb
(mm/yr)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Himalayan
Karakorum‐Jiali
East Kunlun
West Qinling‐Delingha
Haiyuan‐Qilian
West Kunlun
Altyn Tagh
South Tian Shan
North Tian Shan
Altai
Lancang River
Red River
Sanjiang
Xianshuihe
Anninghe‐Xiaojiang
MinShan‐Longmen Shan
Yinchuan Graben
Southeast China costal zone
Qinling‐Dabie
Fenhe‐Weihe
Hebei Plain
Anyang‐Heze‐Linyi
Tanlu
Yin Shan
Yan Shan‐Bohai
15.6 ± 3.3
12.9 ± 3.3
11.2 ± 1.8
3.7 ± 1.8
8.2 ± 1.3
9.7 ± 2.1
8.3 ± 1.7
5.3 ± 1.1
2.9 ± 1.3
8.0 ± 1.1
10.0 ± 1.8
8.2 ± 1.3
1.6 ± 1.7
18.1 ± 1.3
12.7 ± 0.9
2.8 ± 0.8
3.0 ± 0.7
4.9 ± 0.6
1.5 ± 0.6
1.2 ± 0.6
0.5 ± 0.7
0.4 ± 0.9
0.9 ± 0.8
0.9 ± 0.7
1.5 ± 0.7
Mo Rate
(1018 N m/yr)
Starting
Year
Accumulated Mo
(1020 N m)
Released
Seismic Mo
(1020 N m)
25.20 ± 5.20
13.90 ± 3.10
14.60 ± 2.50
1.92 ± 0.97
6.50 ± 1.09
3.49 ± 0.77
6.47 ± 1.32
2.76 ± 0.54
0.95 ± 0.32
2.20 ± 0.30
5.41 ± 0.95
3.14 ± 0.50
0.59 ± 0.21
4.10 ± 0.30
5.64 ± 0.39
1.45 ± 0.36
0.57 ± 0.13
1.64 ± 0.21
0.33 ± 0.14
0.16 ± 0.07
0.18 ± 0.10
0.46 ± 0.21
0.48 ± 0.27
0.41 ± 0.80
0.38 ± 0.13
1800
1900
1890
1600
1800
1880
1900
1850
1750
1850
1850
1900
1850
1850
1700
1600
1500
1400
1400
1000
1400
1400
1500
1900
1400
52.20 ± 10.70
14.80 ± 3.35
17.10 ± 2.96
7.81 ± 3.96
13.40 ± 2.26
4.43 ± 0.97
6.92 ± 1.41
4.34 ± 0.84
2.45 ± 0.82
3.46 ± 0.46
8.49 ± 1.49
3.36 ± 0.54
0.92 ± 0.32
6.43 ± 0.46
17.30 ± 1.20
5.88 ± 1.45
2.87 ± 0.65
9.94 ± 1.29
1.98 ± 0.87
4.65 ± 2.16
0.99 ± 0.42
1.11 ± 0.62
2.41 ± 1.36
0.23 ± 0.10
2.31 ± 0.79
136.00 ± 81.60
17.70 ± 10.6
23.20 ± 13.90
3.62 ± 2.17
98.40 ± 58.90
3.93 ± 2.35
2.61 ± 1.56
44.90 ± 26.90
22.70 ± 13.60
15.40 ± 9.24
7.81 ± 4.67
1.71 ± 1.02
2.05 ± 1.23
9.25 ± 5.53
34.30 ± 20.60
33.80 ± 20.30
17.80 ± 10.70
7.04 ± 4.22
0.09 ± 0.05
64.10 ± 38.30
3.68 ± 2.20
0.80 ± 0.48
81.20 ± 48.60
0.21 ± 0.13
26.60 ± 15.9
Moment Deficits
1020 N m (Mw)c
‐
‐
‐
4.19 (7.7)
‐
0.50 (7.1)
4.31 (7.7)
‐
‐
‐
0.68 (7.1)
1.65 (7.4)
‐
‐
‐
‐
‐
2.90 (7.6)
1.89 (7.4)
‐
0.31 (6.9)
‐
0.02 (6.2)
‐
a
The numbering of the seismic belt is the same as in Figure 10.
The slip rates are mean values for the seismic belts.
c
Only moment deficits are shown. Number in parentheses indicates the equivalent moment magnitude if all the moment deficits are released by one
earthquake.
b
Tibetan Plateau is 163 ± 30 × 1018 N m/yr, about 88% of
that in the entire Chinese mainland. The predicted rates of
moment accumulation for major fault systems are listed in
Table 3. The highest rates are found on the Himalayan
Thrust System plate boundaries (25.2 ± 5.2 × 1018 N m/yr).
Other faults with high moment accumulation rate in this
region include the Karakorum‐Jiali fault (13.9 ± 3.1 ×
1018 N m/yr), the Xianshuihe‐Xiaojiang fault (9.74 ±
0.69 × 1018 N m/yr), the Kunlun fault (18.1 ± 3.3 × 1018 N m/
yr), the Haiyuan‐Qilian fault (6.50 ± 1.09 × 1018 N m/yr),
and the Altyn Tagh fault (6.47 ± 1.32 × 1018 N m/yr). The
Xinjiang region has the second highest moment accumulation rate in mainland China (Figure 9), consistent with the
relatively intense seismicity there (Figure 1).
[34] Because of the low fault slip rates in eastern China,
moment accumulation rate there is considerably lower: 5 ±
2 × 1018 N m/yr for the entire north China, and 4 ± 1 ×
1018 N m/yr for south China.
5.2. Seismic Moment Release
[35] Seismic moment (Mo, in Newton meters) released by
an earthquake can be estimated from its moment magnitude
(Mw):
Mw ¼ ð2=3Þ log Mo 6:03
ð5Þ
However, most earthquakes in the Chinese catalog are given
in surface wave magnitude (Ms). Because the difference
between the Mw and Ms is usually small, we treated all
magnitudes in the catalog as Mw in our estimation of seismic
moment release. The error of magnitude in the Chinese
earthquake catalog is estimated to be ±0.2 [Liu et al., 2006].
[36] Using equation (5), we estimate the total scalar
seismic moment released in mainland China during 1920–
2007 to be 170.45 ± 127.33 × 1020 N m, much lower than
the predicted 197.95 ± 36.38 × 1020 N m that would have
accumulated during this period. The difference is the
moment deficit, which is equivalent to the moment released
by an Mw 8.2 earthquake. While this moment deficit provides some sense of the seismic potential in mainland China,
earthquakes occur by rupturing individual faults. Hence we
need to examine moment deficits on each fault or fault
segment, which is not feasible for the scale of this study.
Instead, we would discuss the moment deficit for each of the
seismic belts, which are the simplified fault systems.
5.3. Moment Deficit on Seismic Belts
[37] We define 25 major seismic belts in mainland China
based on seismicity and active faults (Figure 10), all of them
are the boundary faults of our block model (Figure 3). The
simplification is reasonable because all known M ≥ 8.0
earthquakes occurred on these block boundary faults, so are
more than 80% of M = 7.0–7.9 events [Zhang et al., 2005]
(Figure 10).
[38] To balance the moment on each seismic belt, we need
to consider a period as long as possible that spans one or
more seismic cycles and have complete record of large
earthquakes. Although the earliest earthquake recorded in
the Chinese mainland was a M 7.0 event in 23rd century B.C.
[Division of Earthquake Monitoring and Prediction, State
Seismological Bureau, 1995], the record is incomplete, espe-
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Figure 10. Major seismic belts in mainland China. Blue dots indicate epicenters of historic earthquakes
before 1900; red dots indicate earthquakes during 1900–2010 (mostly instrumental records). Number
shows the seismic belts listed in Table 3.
cially for the early centuries. Furthermore, the situation
varies greatly from region to region. In western China, the
earthquake record is short, often available only for the past
century. The seismic belts with long historical record are
regions with long history of human habitation, such as near
the north Tian Shan belt, the Xianshuihe belt, the Anninghe‐
Xiaojiang belt, and the Longmen Shan‐Min Shan belt. The
relatively long earthquake records (likely complete for
M > 6.0 since 1851) and high slip rates on the Xianshuihe
and the Anninghe‐Xiaojiang seismic belts means that the
records likely covered at least one earthquake cycle [Wen
et al., 2008]. In eastern China, the historical earthquake
record is nearly 3000 years long because of the long history
of human habitation [Division of Earthquake Monitoring and
Prediction, State Seismological Bureau, 1995], but the recurrence intervals are also long because of the low slip rates. In
north China the catalog for M ≥ 6.0 events is likely complete
since 1300 [Huang et al., 1994].
[39] In Figure 11a we show the seismic moment released
on each seismic belt in the most recent period. The starting
year for this period varies for each belt, depending on the
time span for which we likely have a complete record for
M ≥ 6.0 events for the belt (Table 3). The highest moment
release is found in the Himalayan seismic belt. Other
seismic belts of high moment release include the Haiyuan‐
Qilian belt, the south and north Tian Shan belts, the
Anninghe‐Xiaojiang belts, the Fenhe‐Weihe belt, and the
Tanlu belt, all with M ≥ 8.0 events in the period considered.
Figure 11b shows the predicted moment accumulation for
each seismic belt during the same periods as considered in
Figure 11a.
[40] Comparing Figure 11a with Figure 11b, we identify
nine seismic belts with significant moment deficit (i.e., more
accumulation than release) (Figure 12). Of particular concern are the seismic belts with large moment deficit in north
China because of the high density of human populations
there.
6. Discussion
[41] The elastic block models assume that crustal deformation is concentrated along fault zones bounding rigid
crustal blocks. This is a reasonable approximation for crustal
deformation over the timescales (less than 103 years) considered here. Many studies have shown that in such short
timescales, crustal strain is mainly elastic [Meade and
Hager, 2005b; Pollitz, 2003; Yang and Liu, 2010]. On the
other hand, some authors have argued that crustal deformation in Chinese continent is continuous [England and
Houseman, 1986; England and Molnar, 2005; Royden et
al., 1997; Royden et al., 2008; Vergnolle et al., 2007;
Zhang et al., 2004]. The difference between the rigid block
models and those of continuous deformation depends on
the scales of blocks. Thatcher [2007] has suggested that the
block models and the continuum models converge as the
number of faults increase and the block size decreases.
Zhang and Gan [2008] have presented a model combining
rigid block motion with continuous deformation to describe
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Figure 11. (a) Estimated seismic moment released by earthquakes in major seismic belts during the most
recent period (the starting year differs for each belt depends on the completeness of the earthquake catalog, see text for details). (b) Predicted moment accumulation during the same period as for moment
release in Figure 11a. Numbers are in 1020 N m/yr.
the present‐day crustal deformation within continental
China. Vergnolle et al. [2007] show that crustal kinematics
of a large part of Asia is apparently consistent with block‐ or
plate‐like motions, and continuous internal strain is mostly
limited to the Tibetan Plateau.
[42] One major result of this study is the self‐consistent
slip rates on all major faults in mainland China (Table 2 and
Figure 8). Although slip rates on many of these faults have
been determined in previous GPS studies [Calais et al.,
2006, 2003; Chen et al., 2004; Deng et al., 2002; Gan
et al., 2007; He et al., 2003; King et al., 1997; Li et al.,
2009; Meade, 2007; Shen et al., 2005, 2001; Thatcher,
2007; Wang et al., 2001, 2008; Yang et al., 2009; Zhang
et al., 2004, 2007], most of these studies are focused on
individual faults or on certain region of continental China,
and earthquake cycle on faults are often not considered.
Figure 12. Predicted moment deficit (red) and surplus (blue) for major seismic belts in mainland China.
Values are in 1020 N m/yr. The numbers in parentheses indicate the equivalent moment magnitude of an
earthquake if it releases all the moment deficits in the seismic belt.
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Geological estimates, on the other hands, are limited in
numbers and often show large discrepancies for the same
fault, such as for the Altyn Tagh fault and the Haiyuan fault
(Table 2). Hence the predicted total slip rates on all major
faults in this study provide a useful framework for understanding active tectonics and associated earthquake hazard in
mainland China. Interpreting the results presented here, however, requires understanding the limitations and uncertainties
of the model and data, which are briefly discussed in this
section.
6.1. Stability of the Block Model
[43] The results of the elastic block model can be affected
by the geometry of the blocks, which is necessarily a simplification of nature’s complex fault systems. Our block
model is based on previous studies of geological structures,
fault activity, crustal motion, and seismicity [Chen et al.,
2004; Deng et al., 2002; Gan et al., 2007; Han et al.,
2003; Meade, 2007; Shen et al., 2005; Thatcher, 2007;
Zhang and Gan, 2008; Zhang et al., 2003]. To see whether
or not reasonable variations of the block geometry significantly alter our results, we tested a number of block configurations. For example, we adjusted the block geometry in
the southeastern and northeastern parts of the Tibetan Plateau and changed the boundary between the Qiangtang
block and the Songpan‐Ganze block. The results are close to
those of our preferred model. The mean residual velocity
between the preferred model and our various test models is
less than 0.05 mm/yr. Other elastic block models have been
applied in the Tibetan Plateau region [Meade, 2007; Shen et
al., 2005; Thatcher, 2007; Wang et al., 2008, 2010] with
different block geometry and GPS data sets; such differences did not lead to significantly different slip rates on the
major faults. Hence our results are not sensitive to reasonable choices of block geometries.
6.2. Uncertainties of the GPS Data
[44] The GPS data used in this work are a compilation of
the results from the Chinese GPS network and many other
groups [Zhang and Gan, 2008]. As such they include some
site velocities with large errors (Figure 2). We removed
some of these outliers using the F test. Including these
outliers in our model does not significantly change our results
but would worsen the fit between the data and the model
results. The mean residual velocity is 1.49 mm/yr, contrasting to 0.91 mm/yr in our preferred model with the
outliers removed. Most of the outliers are located outside of
our block model domain, hence their influence is mainly on
the external boundary faults of our model. Within the model
domain the GPS sites are relatively dense, so the influence
of outliers is limited.
[45] When using GPS data to constrain the block model,
one assumes that the GPS data measure interseismic
deformation [Meade and Hager, 2005b]. It is possible that
some of the GPS data are tainted by postseismic strain.
Wallace et al. [2004] found the occurrences of the 1997
Mw7.6 Manyi earthquake and the 2001 Mw7.8 Kokoxili
earthquake may have reduced the slip rates on the Altyn
Tagh fault. However, the influence of postseismic deformation is likely minor for the continental‐scale model presented here. Furthermore, the sites strongly tainted by
postseismic strain likely appear as outliers that fail our F test
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and are removed in our model. These include a few site
velocities near the epicenter of the 2001 Mw7.8 Kokoxili
earthquake. On the other hand, the GPS site velocities
around Tangshan may include postseismic deformation,
contributing to the misfit there (Figure 6). Another region of
noticeable misfit is in central and southern Tibetan Plateau
due to the lack of GPS data there. Overall, the GPS data are
consistent with the predicted interseismic crustal motion.
The mean residual between the predicted and the GPS
velocities has the normal distribution with the residual
velocity at most sites close to zero (Figure 6).
6.3. Limitation of Seismic Moment Balance
[46] We have attempted to determine the seismic belts
with large moment deficits, but the results need to be interpreted with caution. The major problem comes from the
short and incomplete earthquake records. The long earthquakes records exist mainly for eastern China, but the low
fault slip rates there imply long recurrence intervals. So the
period of complete record of large earthquakes in the catalog
is not long enough to cover a complete earthquake cycle,
making it difficult to balance the moment. This problem is
compounded by the clustering of earthquakes and long
and irregular recurrence intervals that are common for
intracontinental earthquakes [Stein et al., 2009]. The impact
of such problems is illustrated by the 2008 Wenchuan
earthquake (Mw 7.9) that occurred on the Longmen Shan
fault, which has a low slip rate and only moderate seismicity
in the past few centuries. Balancing moment accumulation
and release on the Longmen Shan fault over the past 400 years
would yield a small moment deficit incapable of producing a
large earthquake [Wang et al., 2010]. However, the recurrence interval for large earthquakes on the Longmen Shan is
estimated to be more than 1000 years [Burchfiel et al., 2008;
Densmore et al., 2007; Shen et al., 2009; Zhang et al.,
2010]. Because there is no evidence of large earthquakes
on the Longmen Shan fault in the past millennium before the
2008 Wenchuan earthquake [Densmore et al., 2007], balancing moment over the past millennium would yield an
alarmingly large moment deficit (1.15 × 1021 N m) that is
sufficient to explain the 2008 Wenchuan earthquake [Wang
et al., 2010].
[47] Problems may also arise from the simplification of
the seismic zones in our model. For example, the Qinling‐
Dabie fault belt is a Mesozoic suture zone that separates the
north China and the south China cratons. The fault belt itself
is not seismically active, so the predicted moment deficit
along this belt may be better interpreted as indicating strain
energy distributed over the transition zone between the
North China and South China blocks, rather than the
potential for a large earthquake on this belt. Furthermore,
the external boundaries of the model domain are not well
constrained, so the predicted moment deficit along the
southeast China costal zone may not be reliable. Finally, the
predicted moment deficit is a lumped sum for large fault
systems or regions, whereas earthquakes occur on individual
fault segments. With all the limitations, our estimate of
moment deficit on major seismic belts in mainland China
provides some guidance for future studies. Further GPS
measurements across individual active faults will allow
refined block models to estimate slip rates on these faults or
fault segments, which, with more complete earthquake his-
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tory from paleoseismic studies, will lead to better assessment of earthquake hazards.
7. Conclusions
[48] We have determined the self‐consistent slip rates on
all major active faults in mainland China using a three‐
dimensional elastic block model and the recently updated
GPS data. The slip rates show a sharp contrast between
western China (high) and eastern China (low), roughly
separated along the 105°E longitude, or the south‐north
seismic belt. The highest slip rates (>10 mm/yr) are mostly
found on faults bounding and within the Tibetan Plateau,
reflecting the impact of the ongoing Indo‐Asian collision.
The faults in northwestern China (the Xinjiang region) have
the second highest slip rates (∼3–8 mm/yr). The Altai faults
show up to 5.4 mm/yr contraction, indicating the far‐field
effect of the Indo‐Asian collision. In contrast, slip rates in
eastern China are much lower (<3 mm/yr). The South China
block moves as a generally coherent block, and slip rates on
major faults in north China vary between 0.5 and 3.0 mm/yr.
The spatial pattern of active tectonics delineated by the fault
slip rates is generally consistent with the intensity of seismic
activity in mainland China.
[49] Using the predicted slip rates and locking depths, we
estimated the rates of moment accumulation on major active
faults and compared them with seismic moment release on
these faults based on the Chinese earthquake catalog. The
results show nine major seismic belts with significant
moment deficits, including the Altyn Tagh fault, the west
Kunlun fault, the Yin Shan fault, and the fault zones in the
southern part of the North China block. These predicted
moment deficits are only suggestive because of the incomplete earthquake history. Further studies in these regions,
especially faults with high moment deficit in north China,
are particularly needed because of the large human populations around these fault zones.
[50] Acknowledgments. This work is supported by the International
Science and Technology Cooperation Program of China (grant
2010DFB20190) and the “Basic Science Research Plan” of the Institute
of Earthquake Science, China Earthquake Administration (grant
02092441). We thank B. Meade for making his elastic block model available, and Weijun Gan for providing the GPS velocity data. Wang’s visit to
the University of Missouri was funded by a university matching fund to
NSF‐PIRE grant 0730154. This paper has been improved by the constructive comments by the Associate Editor and two anonymous reviewers.
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J. Cao, X. Shen, H. Wang, and G. Zhang, Institute of Earthquake
Science, China Earthquake Administration, 63 Fuxin Rd., Haidian
District, Beijing 100036, China. ([email protected])
M. Liu, Department of Geological Sciences, University of Missouri,
101 Geology Bldg., Columbia, MO 65211, USA.
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