Geoscience Reference
In-Depth Information
5
Intraplate earthquakes in North China
MIAN LIU, HUI WANG, JIYANG YE, AND CHENG JIA
Abstract
North China, or geologically the North China Block (NCB), is one of the
most active intracontinental seismic regions in the world. More than 100 large
(M
>
6) earthquakes have occurred here since AD 23, including the 1556 Huax-
ian earthquake (M 8.3), the deadliest one in human history with a death toll of
830,000, and the 1976 Tangshan earthquake (M 7.8) which killed
250,000
people. The cause of active crustal deformation and earthquakes in North China
remains uncertain. The NCB is part of the Archean Sino-Korean craton; ther-
mal rejuvenation of the craton during the Mesozoic and early Cenozoic caused
widespread extension and volcanism in the eastern part of the NCB. Today, this
region is characterized by a thin lithosphere, low seismic velocity in the upper
mantle, and a low and flat topography. The western part of the NCB consists of
the Ordos Plateau, a relic of the craton with a thick lithosphere and little inter-
nal deformation and seismicity, and the surrounding rift zones of concentrated
earthquakes. The spatial pattern of the present-day crustal strain rates based
on GPS data is comparable to that of the total seismic moment release over
the past 2,000 years, but the comparison breaks down when using shorter time
windows for seismic moment release. The Chinese catalog shows long-distance
roaming of large earthquakes between widespread fault systems, such that no
M
7.0 events ruptured twice on the same fault segment during the past 2,000
years. The roaming of large earthquakes and their long sequences of after-
shocks pose serious challenges to the current practice of seismic hazard assess-
ment, and call for a fundamental paradigm shift for studies of intracontinental
earthquakes.
