HR: 0830h
AN: G31B-0714    [PDF]
TI: Stress Transfer, Thermal Unrest, and Implications for Seismic Hazards Associated with the Norris Uplift Anomaly in Yellowstone National Park
AU: * Wicks, C
EM: cwicks@usgs.gov
AF: U. S. Geological Survey, MS 977, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Thatcher, W
EM: thatcher@usgs.gov
AF: U. S. Geological Survey, MS 977, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AU: Dzurisin, D
EM: dzurisin@usgs.gov
AF: U. S. Geological Survey -- David A Johnston Cascades Volcano Observatory, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, WA 98683 United States
AB: Deformation maps of Yellowstone, inferred from satellite interferometric synthetic aperture radar (InSAR), delineate a large area of uplift (30 by 40 km) centered under the north rim of the Yellowstone caldera. Since this area is nearly centered on the Norris Geyser Basin (NGB), we call it the Norris Uplift Anomaly (NUA). The NUA began inflating in 1997, and had inflated a maximum of $\sim$125 mm through the summer of 2002 (the latest InSAR data available). This inflation has led to dilatation of the surface above the uplift of an estimated 8.5 microstrain. The pressure decrease from this dilatation, concentrated in the depth interval 0-2 km, could lead to an increase in advective heat transported to the surface, producing the currently observed thermal unrest. The spring and summer of 2003 has been a time of vigorous thermal unrest in the NGB of Yellowstone National Park. Unrest began with the eruption of Steamboat Geyser in May 2000, and has intensified this spring and summer with the eruption of Porkchop Geyser (dormant since 1989), the formation of a 75 m line of fumaroles just north of NGB, and a general trend of increasing spring and ground temperatures in NGB. The National Park Service has closed some footpaths in the geyser basin owing to near-boiling ground temperatures. The uplift has also led to an increase in seismic hazard potential in the area of uplift. The calculated stress field from the modeled shallow dipping dike that best fits the InSAR observations through 2002 is over 0.4 MPa at a normal fault that slipped during (and at the 4 km hypocentral depth of) a nearby M$_{L}$ 6.1 earthquake in 1975. Stress changes an order of magnitude less may be responsible for triggering normal-faulting earthquakes.
DE: 1243 Space geodetic surveys
DE: 6924 Interferometry
DE: 7223 Seismic hazard assessment and prediction
DE: 8424 Hydrothermal systems (8135)
SC: Geodesy [G]
MN: 2003 Fall Meeting