Intraplate earthquakes in North China - Intraplate Earthquakes - page 111

5.5.3 Large instrumentally recorded earthquake

Several earthquakes larger thanM7.0 in the North China Plain have been recorded by instru-
ments since 1960 ( Figure 5.2 ) . The most devastating ones include the Xingtai, Haicheng,
and Tangshan earthquakes.

The 1966 Xingtai earthquake (Ms 7.2)
Between March 8 and 29, 1966, a cluster of five earthquakes larger than M 6.0 occurred
in the Xingtai region of the Hebei Province. The largest one was an Ms 7.2 event which
occurred on March 22; the maximum intensity reached X in the epicentral region. These
earthquakes destroyed more than 5 million buildings, killed 8,064 people and injured

38,000 (Seismological Bureau of Hebei Province, 1986 ) .
The earthquake cluster occurred on a NNE-trending right-lateral fault along the Sulu
graben (Chung and Cipar, 1983 ; Xu et al ., 1988 a ). The rupture length is about 50 km,
and the maximum right-lateral strike-slip displacement was 1.0 m (The Geodetic Survey

Brigade for Earthquake Research, 1975). The focal depths of these events range from 9 to
25 km (Chen et al ., 1975 ) , consistent with the depths of aftershocks.

The 1975 Haicheng earthquake (Ms 7.3)
The 1975Haicheng earthquake occurred on February 4 in theHaicheng region, Northeastern
China (122.83

N), on the northwest-trending Jingzhou-Haicheng fault. The focal
depth is 16-21 km, with a surface rupture of

° E, 40.70 °

50 km length. The maximum left-lateral slip
is 0.55 m (Jones et al ., 1982 ; Zhu and Wu, 1982 ) .
The Haicheng earthquake's maximum intensity reached IX, yet the human casualties,
with 1,328 killed and 16,980 injured, were much fewer than usual thanks to a successful
prediction (Scholz, 1977 ) . A major factor leading to the prediction was a long foreshock
sequence: more than 500 of them were recorded within 4 days before the mainshock (Jones
et al. , 1982 ) . Wang et al .( 2006 ) found that the role of foreshocks in this prediction was
more psychological than scientific: the jolts and damage from increased seismicity in the
preceding months worried earthquake workers and the general public, and the intensified
foreshocks in the last day before the mainshock prompted some local officials to order an
evacuation. In other places where official orders were not issued, the increased seismicity
caused many residents to evacuate voluntarily.

The 1976 Tangshan earthquake (Ms 7.8)
The Great 1976 Tangshan earthquake occurred in the morning of July 28. The earthquake
struck Tangshan, an industrial city 150 kilometers east of Beijing. In a brief moment, the
earthquake destroyed the entire city and killedmore than 242,000 people (Chen et al ., 1988 ) .
The maximum intensity reached XI in the epicentral region. An Ms 7.1 event followed 19
hours after the mainshock. The length of surface rupture produced by the mainshock is