Intraplate earthquakes in North China - Intraplate Earthquakes - page 104

the present-day slip rate is less than 1 mm/yr (Wang et al ., 2011 ) , its rupture in 1668 caused
the Ms 8.5 Tancheng earthquake.
The northern margin of the North China Plain is bounded by the Zhangjiakou-Penglai
fault, a complex, NW-SE-trending fault system that is up to a few tens of kilometers wide as
it extends to the coastal regions ( Figure 5.2 ) . Its intersections with a system of NE-trending
faults in the North China Plain, including the Tanlu fault, are the source regions of a number
of destructive earthquakes.
The North China Plain, between the Shanxi rift and the Tanlu fault, has a complex
systems of faults, mainly NNE-trending, which are covered by thick Quaternary sediments,
with little or no surface traces (Deng et al ., 2003 ) . Some of these faults, including the
Xingtai-Hejian-Tangshan fault zone, were recognized only after the destructive 1966
Xingtai earthquake (M 7.2) and the 1996 Tangshan earthquake (M 7.8).

5.3 Active tectonics and crustal kinematics

North China, with its dense population and intense seismicity, is one of the best studied
regions in China. A “Map of Active Tectonics of China,” at a scale of 1:4 million, identified
more than 200 active tectonic zones (Deng et al ., 2003 ) . This map delineates the active
tectonic belts of China that bound relatively aseismic blocks.
The GPS network in North China was established in 1992; it was significantly improved
with the establishment of the Crustal Motion Observation Network of China (CMONOC)
in 1998. About 300 CMONOC survey mode GPS stations are located in North China,
covering effectively all the known regional active faults ( Figure 5.4 ) . Shen et al . ( 2000 )
found that regional deformation in North China is dominated by left lateral slip ( 2 mm/yr)

across the east-southeast-trending Zhangjiakou-Penglai seismic zone and extension (

4
mm/yr) across the north-northeast-trending Shanxi rift, which could be comparable with
the

1.0 mm/yr estimated from seismic moment data (Wesnousky et al ., 1984 ) and 0.5-1.6
mm/yr averaged over the Late Pliocene-Quaternary time (Zhang et al ., 1998 ) . However,
using a more complete dataset, He et al .( 2003 ) found no clear signal of extension across the
Shanxi rift; they attributed the discrepancy with geological extension rate to time-dependent
extensional processes.

5.4 Strain rates and seismicity

Using the GPS data from China's CMONOC network, Liu and Yang ( 2005 ) calculated
the scalar strain rates, defined as E 2 ε φλ ε φλ ) 1 / 2 , where ϕ and λ are

longitude and latitude, respectively, in North China ( Figure 5.5 ) . The higher strain rates
are found in the North China Plain and around the Ordos Block. The Shanxi rift system,
which has had many large earthquakes in the past 2,000 years ( Figure 5.1 ) , surprisingly
shows relatively low strain rates. This is consistent with the GPS results (He et al ., 2003 ) ,
and may be related to the seismic quiescence within the Shanxi rift in the past 300 years
(Liu et al ., 2007 , 2011).

= ( ε φφ ε φφ + ε λλ ε λλ +