Intraplate earthquakes in North China - Intraplate Earthquakes - page 115

Figure 5.9 Conceptual models for the differences between interplate (a) and intraplate (b) earth-
quakes. For interplate earthquakes, the plate boundary fault is loaded at a constant rate by the steady
relative plate motion, causing quasi-periodic earthquakes to concentrate along the plate boundary. In
plate interiors, slow far-field tectonic loading is shared by a complex system of interacting faults. On
each fault, the loading rate may be variable, and earthquakes may shut off on one fault and migrate
to another.
( Figure 5.9 ) . Plate boundary faults are loaded at constant rates by the steady relative
plate motion. Consequently, earthquakes concentrate along the plate boundaries, and some
quasi-periodic occurrences may be expected ( Figure 5.9a ) , although the temporal patterns
are often complicated (Jackson and Kagan, 2006 ) . In contrast, in mid-continents the tec-
tonic loading is shared by a complex system of interacting faults spread over a large region
( Figure 5.9b ) , such that a large earthquake on one fault could affect the loading rates on
remote faults (Li et al ., 2009 ) . Because the slow tectonic loading is shared by many faults
in mid-continents, individual faults may remain dormant for a long time and then become
active for a short period, while seismicity moves to other faults.
5.7 Implications for earthquake hazards
The complex spatiotemporal patterns of earthquakes in North China pose serious challenges
to the assessment of earthquake hazards. The current practice of hazard assessment is
heavily influenced by the occurrence of previous large earthquakes ( Figure 5.10 ) , assuming
that large earthquakes will be likely to repeat on the same faults. This line of reasoning
can be traced back to Reid's elastic rebound theory (Reid, 1910 ) , which implies cycles of
energy accumulation and release on a given fault. However, the validity of this premise for
intracontinental earthquakes has been questioned (Stein et al ., 2011 , 2012). In North China,