HR: 1330h
AN: S52F-0183    [PDF]
TI: Localized Weak Zones and Their Role in the Generation of Intraplate Seismic Zones: Effects of Weak Zone Geometry and Rheology
AU: * Joshi, A
EM: ajosh2@uky.edu
AF: Dept. of Mechanical Engineering, Univ. of Kentucky, 151 RGAN, Lexington, KY 40506 United States
AU: Kenner, S J
EM: skenner@uky.edu
AF: Dept. of Geological Sciences, Univ. of Kentucky, 101 Slone Building, Lexington, KY 40506 United States
AB: It has been proposed that earthquake generation within intraplate seismic zones (e.g. the New Madrid Seismic Zone, NMSZ, in the south-central United States) may result from the transient relaxation of a lower crustal weak zone. As the weak zone relaxes, stress is transferred to the overlying seismogenic crust, potentially leading to a geologically short-lived burst of seismicity lasting 10,000's of years. The duration and number of earthquakes in this seismic sequence is dependent on weak zone geometry and rheology. Using finite element techniques which employ contact surfaces to model discrete faulting events, we investigate the relevant model parameter space as it effects the concentration of stress at the base of seismogenic fault. Faulting is modeled using discrete contact surfaces and failure is governed by a maximum shear stress criteria evaluated at each node on the fault surface. Investigated model parameters include weak zone geometry, weak zone rheology (Maxwell and Standard Linear Solid, SLS), earthquake stress drop, background tectonic stress, and maximum shear stress at failure. Of particular interest is the effect of model geometry and rheology. Wider weak zones transfer stress to areas potentially remote from fault leading to initially slower slip-rates. After complete relaxation, however, the cumulative moment is greater then for the narrow weak zone case. Prior models have considered only a Maxwell viscoelastic weak zone, which has no long-term elastic strength. This may not be a realistic intraplate material behavior. Thus, this study also considers a SLS weak zone which has a long-term elastic strength. This may be more realistic, though the long term elastic strength becomes an additional parameter which must be defined. Although the amount of stress available for transfer to the seismogenic zone is potentially decreased when a SLS is used, for certain parameters, 2-4 earthquakes still occur during the relaxation process. A number of different effective rheologies and geometries are considered and results have been compared to geologic observations in the NMSZ.
DE: 1208 Crustal movements--intraplate (8110)
DE: 3210 Modeling
DE: 7209 Earthquake dynamics and mechanics
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting