Intraplate earthquakes in North China - Intraplate Earthquakes - page 112

more than 47 km, and left-lateral slip is 1.5-2.3 m (Guo et al ., 2011 ) . The seismic moment
released by the mainshock was 11.7 10 19 Nm.

The earthquake occurred within the broad fault system bounding the northern margin of
the North China Plain. The hosting fault for the mainshock is a northeast-trending strike-slip
faulting system with a dextral bend in the middle that divides the fault into the southern
and northern segments (Nabelek et al ., 1987; Shedlock et al ., 1987 ) .

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5.6 Spatiotemporal patterns of large earthquakes

The spatiotemporal pattern of seismicity for a region is essential for hazard assessment.
Establishing such a pattern, however, is difficult for most intracontinental regions because
of the slow loading, infrequent large earthquakes, and incomplete earthquake records. The
situation is better for North China - with its relatively frequent large earthquakes and long
historic records, useful insight may be obtained.

5.6.1 Long-distance roaming of large earthquakes

Here we show the spatiotemporal occurrence of large earthquakes in North China during
the past 700 years. For this relatively recent period, the catalog is likely complete for M

6

events (Huang et al ., 1994 ) and it includes 49 M 6.5 events and at least four earthquakes

of M 8, described in the previous section. Before the 1303 Hongdong earthquake,

large earthquakes in North China were concentrated along the Weihe and Shanxi rifts and
scattered over the North China Plain ( Figure 5.7 a ). The Hongdong earthquake (M 8.0)
occurred within the Shanxi rift, followed by the 1556 Huaxian earthquake (M 8.3) in
the Weihe rift ( Figure 5.7 b ). During this period, seismicity seemed to be concentrated
within the Weihe-Shanxi rift systems, which would fit the model for rift zones to be the
main host structures of intraplate earthquakes (Johnston and Kanter, 1990 ) . However,
the next large earthquake, the 1668 Tancheng earthquake (M 8.5), did not occur within
the rift systems but more than 700 km to the east, on the Tanlu fault zone, which had
little deformation through the late Cenozoic and only moderate previous seismicity. A
decade later, another large event, the 1679 Sanhe earthquake (M 8.0), occurred only 40 km
north of Beijing in a fault zone with limited previous seismicity and no clear surface
exposure ( Figure 5.7 c ). Then, in 1695, the Linfen earthquake (M 7.5-8.0) occurred in
the Shanxi rift again, near the site of the 1303 Hongdong earthquake but on a different
fault. Since then the Shanxi and Weihe rifts have been quiescent for more than 300 years,
with only a few moderate earthquakes. Meanwhile, seismicity in the North China Plain
apparently increased, producing three damaging earthquakes in the past century: the 1966
Xingtai earthquakes, the 1975 Haicheng earthquake, and the 1976 Tangshan earthquake
( Figure 5.7 d ). These three large earthquakes were unexpected and occurred on previously
unrecognized faults.