- © 2010 by the Seismological Society of America
Seismically active intraplate continental settings are characterized by relatively low strain rates, but they nonetheless display evidence of active faulting and seismicity. Examples of these tectonic environments include seismically active areas of northern Eurasia, central India, Australia, and the U.S. mid-continent (e.g., Sykes 1978; Johnston 1996). They are characterized by low heat flow (e.g., Kusznir and Park 1984), relatively thick lithosphere, and presumably low strain rates (∼10–10–10–12 yr–1) (Gordon 1998). Yet in only a handful of these environments have geodetic measurements been used to provide constraints on the rates and directions of present-day deformation in these intraplate settings. We present precise geodetic observations and modeling results for one type-example of a continental, intraplate deformation zone: the Wabash Valley seismic zone (WVSZ) in the central United States. We use high-precision campaign-based GPS data from a network of GPS sites in the WVSZ to address evidence for present-day tectonic strain in an intraplate seismogenic zone. This study builds on the results of Hamburger et al. (2002), extending their preliminary one-year observation period (1997–98) to an eleven-year observation cycle (1997–2008). The observed evidence for active crustal deformation of the region is then modeled using a fault-and-block approach, which treats deformation as described by finite, rigid crustal blocks bounded by planar faults (e.g., Thatcher 1995; McClusky et al. 2001; Tapponnier et al. 2001; McCaffrey 2002). The main scientific questions delve into the nature of active deformation in this intraplate zone and address the role of fault systems in the deformation of the North American continent.
The Wabash Valley seismic zone (WVSZ) is a broad, seismically active area located in southern Illinois, southwestern Indiana, and westernmost Kentucky. Situated within the WVSZ is the Wabash Valley fault system (WVFS), a series of parallel NNE-trending normal faults …