The Hydromechanical Wild Card: The Role of Ice Sheets in Crustal Stress Changes, Anomalous Pore Pressures Generation and Seismicity within the Midcontinent Region of North America

New Mexico Institute Of Mining And Technology, Socorro NM

Investigators

Abstract

The midcontent region of the North American craton has experienced a number of large ( > M6) earthquakes beyond the terminus of the Laruentide Ice Sheet during the Holocene and Anthropocene. The mechanisms responsible for these earthquakes are poorly understood. The main goal of this study is to assess the consequences of lithosphere flexure associated with Pleistocene ice-sheet loading on the build up and preservation of pore pressure anomalies and seismicity within the Proterozoic crystalline basement and overlying sedimentary rocks of the Michigan and Illinois Basins. We hypothesize that shear stress build up within the upper crust (10-20 km depth) beyond the ice sheet terminus causes pore pressure increases within low-permeable environments capable of inducing seismic events. Underpressures, such as those observed at the proposed Canadian nuclear waste repository site on the eastern flank of the Michigan Basin, should occur in formerly glaciated areas undergoing rebound today. Using COMSOL, we will develop a two-dimensional geomechanical-hydrologic-solute transport model capable of representing lithosphere flexure and poro-elastic deformation as well as asthenosphere and groundwater flow. We will utilize a simple Mohr-Coulomb failure criteria as a metric for determining regions of the Earth?s crust that are likely to fail. Ground truth for this model will include the position and (where possible) depths of midcontinent Holocene and Anthropocene earthquakes as well as pore pressure/salinity/isotopic data from reservoirs and confining units of the Illinois and Michigan Basins. Isolating high-level nuclear waste requires consideration of future hydrologic and geomorphic conditions on time scale of up to one million years. The results of this project should be especially relevant to nuclear waste isolation programs in countries located at high latitude countries ( > 40o N) such as those in Canada, Sweden, Switzerland, and Finland. All of these countries could experience future glacations. Project results will be made available to the Canadian Nuclear Waste Management Organization (NWMO) and the Swedish Nuclear Waste Management Agency (SKB). This work may also be of benefit to groups studying induced seismicity within the midcontinent by indentifying regions of the Earth?s crust that could preserve high fluid pressures and would be prone to failure. This project will train one graduate student at NM Tech, a minority-serving institution. Effort will be made to recruit a woman and/or an individual from an under-represented group.