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Midcontinent Earthquakes
Presentation by Alexa Haugan and Emily Fitzhenry
Abstract
This presentation opens with a review of the basic mechanism of action of earthquakes, with a
look at the role of faults in the release of stress accumulated by the relative motion of tectonic
plates. The stage will then be set for contrasting these conventional interplate earthquakes with
those that occur within the stable continent, where tectonic loading is instead accommodated by
a complex system of interacting faults. These faults are commonly ancient failed rifts, such that a
large earthquake on one fault could increase the loading rates on remote faults in the system. In
this way, small-scale earthquakes can cluster on the fault system for a while, but they are prone
to random shifts, which present important threats to cities which are not built to withstand the
resulting damages. Examples of such devastation include the historical 1811 New Madrid fault
earthquakes in Missouri, which was heavily documented in qualitative historical documents. In
1976, the mid-continent Tangshan earthquake took the city by surprise, and represents the
second largest death toll ever reported for an earthquake at 240,000 reported fatalities. Finally,
one of the most destructive of recent earthquakes occurred in 2008, in the Sichuan Province of
China; the aftershocks from this earthquake persisted for a period of two weeks. The nature of
midcontinental earthquakes have important implications for the prediction of tectonic hazards.
Because of the very slow and inconstant loading rate of midcontinent earthquakes, they tend to
only be active for a short period after long dormancy, and this infrequency is responsible for the
lack of earthquake records available in most regions. To add to this prediction difficulty, the
midcontinent earthquakes are large, episodic and spatially migrating, in contrast to the more
regular patterns of interplate earthquakes. Modern methods of monitoring these types of
earthquakes are discussed to conclude this review.1
1. Li, Q., Liu, M., and Stein, S. (2011). 2000 years of migrating earthquakes in North China:
How earthquakes in midcontinents differ from those at plate boundaries. Lithosphere
3(2),128–132