HR: 0800h
AN: T51D-0768    [Abstracts]
TI: Local Stress Concentrators in the Crust as the Cause of Intraplate Earthquakes
AU: * Talwani, P
EM: talwani@geol.sc.edu
AF: Department of Geological Sciences, University of South Carolina, 701 Sumter Street, EWSC Building, Columbia, SC 29208, United States
AU: Gangopadhyay, A
EM: abhijit@ig.utexas.edu
AF: Institute for Geophysics, University of Texas at Austin, J.J. Pickle Research Campus, Bldg. 196, 10100 Burnet Road, Austin, TX 78758, United States
AB: Ignoring induced earthquakes associated with anthropogenic activities, and low magnitude swarms (e.g. in Moodus, Connecticut, and Arkansas), we applied a three-fold approach to the study of the seemingly random occurrence of meaningful intraplate earthquakes (IPE), located within large rigid plates characterized by negligible rates of strain accumulation. Analysis of multidisciplinary data from 39 (M >= 5.0) earthquakes spanning 20 intraplate regions, mechanical modeling, and field observations support the contention that IPE are primarily associated with localized pockets of stress concentrators lying within the rigid plates. The commonly observed stress concentrators include intersecting faults with optimal geometry, intrusives having large rigidity contrasts with surrounding rocks, and stress pillows. Suitably oriented faults with kinks, intersections, jogs and step-overs, lying within crustal zones of weakness, account for nearly two-thirds of the larger IPE. Mechanical modeling and comparison with known examples of IPE show that fault systems suitably oriented with respect to S_Hmax are the most likely locations of meaningful IPE. Stress concentrations near shallow granitic plutons, observed in the South Carolina Piedmont, among other places, and supported by mechanical modeling, can account for M < 4.0 events. Stress pillows, which are large, anomalous, and dense bodies in the lower crust within rifts, are found to account for approximately 15 percent of the IPE. In each case, the regions of elevated stresses are very local, comparable to the dimensions of the stress concentrators, demonstrating the need for very dense (<5 km spacing), focused GPS observations, and the futility of the currently employed plate boundary-type configurations (approximately >10 km).
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8107 Continental neotectonics (8002)
DE: 8123 Dynamics: seismotectonics
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting