HR: 11:50h
AN: G12A-07    [Abstracts]
TI: Reconciling Geodetic and Geologic Rates in Fold and Thrust Belts
AU: * Wiltschko, D V
EM: d.wiltschko@tamu.edu
AF: Texas A&M University, Dept. Geology and Geophysics, Center for Tectonophysics, College Station, TX 77843-3115, United States
AB: Although the scales of observation are not the same, thrust fault slip rates based on dated sediments often yield values an order less than those derived from geodesy (cm vs mm/yr). Moreover, the patterns of present surface motions compared to those accumulated over millions of years are somewhat different. For instance, results from the Idaho-Wyoming-Utah thrust belt and the Andes suggest that the initiation of thrusting progresses from hinterland to foreland. Certainty worsens with age because complexity of deformation increases with age, i.e., initiation of younger, deeper thrust fault rejuvenates older, higher ones and thrust sheets may move several times. Although preservation degrades toward the hinterland, thrusting appears to finally turn off from foreland to hinterland. Evidence for out-of-sequence thrusting is not common. Where timing data are unusually good (e.g., Pyrenees), displacement was evidently not constant in either space or time. This episodicity at times scales of 10⁶ yrs may extend to individual thrust sheets. By contrast, geodetic data - which include both elastic strain accumulation and creep - indicate that all structures in southern Taiwan are moving. The frontal portion is slightly more active than areas to the east. Current geodetic motions are largely normal to local thrust fault traces, even coseismic slip such as that of the Chi-Chi earthquake. Fold growth may be nearly as important as fault slip, although greater data density is required. The discrepancy between geodetic and geologic rates may be attributed to the fact that in the two cases different quantities or aggregates of them are being measured. The difference in patterns is attributable to the different time scales of observation.
DE: 1209 Tectonic deformation (6924)
DE: 1744 Tectonophysics
DE: 8002 Continental neotectonics (8107)
DE: 8010 Fractures and faults
DE: 8102 Continental contractional orogenic belts and inversion tectonics
SC: Geodesy [G]
MN: 2007 Fall Meeting