HR: 1330h
AN: T52B-0273    [PDF]
TI: Controls on the Morphological Variability of the Decollement in the Nankai Trough Subduction Zone
AU: * Adamson, S P
EM: sadamson@es.ucsc.edu
AF: Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Moore, C
EM: cmoore@es.ucsc.edu
AF: Department of Earth Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Bangs, N L
EM: nathan@utig.ig.utexas.edu
AF: University of Texas, Institute for Geophysics, 4412 Spicewood Springs Rd., Austin, TX 78759 United States
AU: Gulick, S P
EM: sean@utig.ig.utexas.edu
AF: University of Texas, Institute for Geophysics, 4412 Spicewood Springs Rd., Austin, TX 78759 United States
AU: Moore, G F
EM: gmoore@Hawaii.edu
AF: SOEST, University of Hawaii, 1680 East-West Rd., Honolulu, HI 96822 United States
AB: Decollements form plate boundaries at subduction zones, hence the details of their initiation are of fundamental importance in the development of large fault systems. A key question at Nankai is does the decollement initiate and remain in a singular layer or jump around and if so why? To investigate this issue, we analyzed 3-D seismic reflection data collected off the Muroto Peninsula by a US-Japanese consortium in 1999. We examined seismic profiles and correlated our interpretations to core and log data from ODP sites 1173, 1174, and 808 to determine the physical properties of the decollement from the undeformed incoming sediment to the deformation front. These seismic profiles indicate that substantial along-strike variability characterizes the decollement in the Nankai Trough subduction zone. The decollement forms a series of overlapping splays above an elongate basement high that is approximately 1 km wide, rises 100-150 m above the adjacent low areas, and trends northwest across the survey area. Seismic profiles show the amount of overlap along the decollement above the basement high ranges from 80 m seaward of the deformation front to 40 m at the frontal thrust. These initial observations suggest the basement relief significantly influences the undulating character of the decollement, becoming less of a factor with increased subduction. Other possible influences on the decollement morphology include the variation in stress orientation caused by the basement high and differences in overpressure resulting from along-strike differences in sediment loading. Determination of these factors will provide a better understanding of the controls of decollement formation.
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting