HR: 0830h
AN: S11D-0329    [PDF]
TI: Strong Motion Prediction Within a Basin Located Above the Teton Fault in Wyoming
AU: * O'Connell, D R
EM: geomagic@seismo.usbr.gov
AF: USBR, PO Box 25007 D-8330, Denver, CO 80225-0007 United States
AU: Graves, R W
EM: robert_graves@urscorp.com
AF: URS Corporation, 566 El Dorado St., 566 El Dorado St., CA 91101 United States
AU: Block, L V
EM: lblock@do.usbr.gov
AF: USBR, PO Box 25007 D-8330, Denver, CO 80225-0007 United States
AB: Strong motion estimates were developed for a site near the center of a basin located above the Teton fault near Jackson, Wyoming for scenario M 6.9 to 7.1 normal-faulting earthquakes. A 3D velocity-hypocenter inversion using 1150 earthquakes recorded by the Jackson Lake Seismic Network resolves velocity variations down to a scale of several km and delineates a ~ 4-km-deep low-velocity basin located above the east-dipping Teton fault. Details of basin boundary and internal velocity structure was derived from reinterpretation of existing seismic refraction data, and 2D finite-difference waveform modeling of three microearthquakes (MEQ) located near the perimeter of the basin and recorded on broadband stations near the middle of the basin. The refraction data and MEQ waveform modeling indicate nearly linear vertical velocity gradients within the basin. Published interpretations of the refraction data used constant velocity layers with strong velocity discontinuities within the basin which fail to reproduce strong broadband arrivals that follow direct S-waves by ~ 4-6 s; these arrivals are composed of S-waves and surface waves produced at the basin margins. Reciprocity 3D finite-difference viscoelastic Green's functions were used to synthesize motions for frequencies $< $1 Hz and eight empirical Green's functions (EGF) were used to synthesize $>$ 1 Hz motions. Kinematic finite-fault rupture models were generated with self-similar slip distributions and variable rupture and rise times. A 3D eikonal equation solver was used to calculate first S-wave arrival times for point-source summations of EGF's. The dip of the Teton fault is not well constrained; dips of 35, 45, and 60 degrees where used to synthesize ground motions. For a 35-degree fault dip, directivity produces factor of two stronger peak responses on the fault perpendicular component than the fault parallel component for all periods. For periods $>$ 0.7 s and a 60 degree fault dip, peak motions were stronger on the fault parallel component than the fault perpendicular component; the strongest arrivals on the fault parallel component are associated with basin-edge waves. The top 5 km of the Teton fault is located within 2-3 km of the western edge of the basin. The western edge of the basin acts as a strong secondary seismic source for sites within the basin; basin-edge S-waves close to the fault are nearly critically reflected for sites near the center of the basin and produce large acceleration and velocity responses that extend the duration of strong shaking by $>$ 10 s within the central portion of the basin.
DE: 7212 Earthquake ground motions and engineering
DE: 7221 Paleoseismology
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 8107 Continental neotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting