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This indicates that the intense seismicity recorded in North China in the past 2,000 years
is a close reflection of the long-term strain energy accumulation and release. One major
mismatch is along the northern margin of the Ordos Plateau, where the relatively low
seismic moment release contradicts the high long-term strain energy predicted by the
model. A similar discrepancy was found by Wang et al .( 2011 ) , who derived the slip rates
on major fault zones in continental China and compared the rates of moment accumulation
with that released by recorded earthquakes. This inconsistency between lowmoment release
and high strain energy may indicate a surplus of moment along the northern boundary of
the NCB.
In general, however, seismic moment release, which is limited by the incomplete earth-
quake catalog, is incompatible with strain rates derived from GPS measurements. To
illustrate the bias of inferred spatiotemporal patterns of seismicity from the incomplete
earthquake record, Figure 5.6 plots the spatial distribution of moment release within a
250-year time window in North China in the past 750 years, a period of the most complete
earthquake record in the Chinese catalog. Note that the spatial pattern of moment release
within each time window differs from all others, and none of them is comparable with the
strain rates derived from the GPS data ( Figure 5.5a ) . These results highlight the complex
spatiotemporal patterns of intracontinental earthquakes, and the problem of long recurrence
time and short and incomplete records. The apparent consistency between the total seismic
moment release and the strain rates based on GPS data in North China is an exception rather
than the norm; this can be largely attributed to the more than 2,000-years of earthquake
records in North China. The catalog is much shorter in other mid-continents. In the Central
and Eastern United States, the historic catalog only extends for 200 years or so, therefore
the spatial pattern of seismicity from these records may not be a reliable indicator for
the long-term seismicity or what seismic activity will look like in the next few hundred
years.
5.5 Seismicity
North China has the most complete earthquake records in China because it is the cradle
of the Chinese civilization. The ancient Chinese regarded earthquakes and other natural
hazards as the wrath of heaven; these events were faithfully recorded by the government.
The earliest written record of earthquakes in North China may be traced back to the twenty-
third century BC (Gu et al ., 1983 ) ; however, the record is likely incomplete, and most of
the early records are sketchy. Recent paleoearthquake studies, mainly through trenching,
have extended the earthquake history in many sites (Xu et al ., 2002a ) .
5.5.1 Paleoseismicity
Most paleoseismic studies in North China have been focused on the rift zones around the
Ordos Plateau. Along the northern edge of the Ordos Block, Ran et al .( 2003a ) identified
62 paleo-earthquakes in the late Quaternary, 33 of which occurred in the Holocene. They
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