STRESS EVOLUTION AND SEISMICITY WITHIN THE NEW MADRID SEISMIC ZONE

Intraplate earthquakes within the stable interior of the North America plate are surprisingly common, large, and poorly understood. The New Madrid Seismic Zone (NMSZ), with three large events (M=7.0-7.5) in 1811-1812, is the most prominent intraplate seismic zone within the stable North America plate. However, most of the post-1811-1812 moderate events (M>5) occurred not within the seismically defined NMSZ but in the surrounding regions. We have simulated stress evolution in the NMSZ and surrounding regions following the 1811-1812 events. Our results show that re-accumulation of Coulomb stress within the NMSZ following the 1811-1812 events is slow and always lags behind that in the surrounding regions, where the relatively strong crust could support the stress released by the 1811-1812 events. The regions with the predicted highest Coulomb stress increase are found in southern Illinois and eastern Arkansas, consistent with the distribution of moderately sized (M>5) earthquakes following the 1811-1812 NMSZ events. We have combined the NMSZ model with a regional-scale stress evolution model to better understand the interplay between local and regional tectonic processes in controlling seismicity in the NMSZ and other intraplate seismic zones in the eastern-central North American plate.