Intraplate earthquakes in North China - Intraplate Earthquakes - page 114

Figure 5.8 (a) Bottom two panels show occurrence and magnitude (M 4.0) of earthquakes in

the North China Plain and the Shanxi-Weihe rifts. Top panel compares the time-averaged rate of
seismic moment release (Nm/yr) between them (tones are correlated with those in the bottom panels).
Dashed lines are for older intervals, wherein some events are likely unrecorded. Gray bands indicate
uncertainties associated with an estimated ± 0.3 error in the magnitudes, which were based on the
maximum intensity and the radius of the affected area (Ma, 1989 ) . (b) Similar to (a) for the comparison
of moment release between the Weihe and the Shanxi rifts. After Liu et al . ( 2011 ) .

other, with increases in one corresponding to decreases in the other. Similar correlation
exists between the Shanxi-Weihe rift system and the faults within the North China Plain
( Figure 5.8 ) . These results suggest that the fault systems in North China are mechanically
coupled with each other.

5.6.3 A conceptual model for mid-continental earthquakes

These spatiotemporal patterns of earthquakes are not unique to North China; similar obser-
vations have been made in other mid-continents including Australia (Clark and McCue,
2003 ) and northwest Europe (Camelbeeck et al ., 2007 ) . In the Central United States, the
Meers fault in Oklahoma had a major earthquake about 1,200 years ago but is inactive
today (Calais et al ., 2003 ) . The New Madrid seismic zone, which has experienced several
large earthquakes in the past few thousand years including at least three M 6.8 events

in 1811-1812 (Johnston and Schweig, 1996 ; Tuttle et al ., 2002 ; Hough and Page, 2011 ) ,
shows no significant surface deformation today (Calais and Stein, 2009 ) and its activity
may be ending (Newman et al ., 1999 ; Calais and Stein, 2009 ; Stein and Liu, 2009 ) .
The roaming of large earthquakes between widespread fault systems illustrates fun-
damental differences between earthquakes in mid-continents and at plate boundaries