HR: 1340h
AN: T53A-1404    [Abstracts]
TI: Imaging the Subducting Pacific Plate Beneath the Mariana Forearc
AU: * Oakley, A J
EM: aoakley@hawaii.edu
AF: Dept. of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd., Honolulu, HI 96822
AU: Taylor, B
EM: taylorb@hawaii.edu
AF: Dept. of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd., Honolulu, HI 96822
AU: Chapp, E L
EM: chapp@hawaii.edu
AF: Dept. of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd., Honolulu, HI 96822
AU: Moore, G F
EM: gmoore@hawaii.edu
AF: Dept. of Geology and Geophysics, SOEST, University of Hawaii at Manoa, 1680 East West Rd., Honolulu, HI 96822
AU: Goodliffe, A M
EM: amg@ua.edu
AF: Dept. of Geological Sciences, University of Alabama, 202 Bevill Building, Tuscaloosa, AL 35487
AB: Three pairs of multi-channel seismic (MCS) profiles near 15N, 16.5N and 18N image the subducting Pacific Plate from the outer trench rise to beneath the Mariana forearc. The subducting oceanic crust and superposed seamounts are deformed by plate flexure and cut by the resulting normal faults. Pacific Plate Moho is imaged 2.1 seconds TWTT below basement on the northern profile. The Mariana Trench deepens from about 7.5 km near 18N to 9 km at 14.5N. Beneath the outer forearc we observe a prominent, low frequency reflection from the top of the down-going plate. The slab reflection is strongest and most continuous on the southern profile where it can be traced 70 km arc-ward from the trench axis. The subducting slab is also imaged on 8 shorter crossing profiles. Teleseismic earthquake data poorly constrain the location of the slab in the outer forearc because of large depth uncertainties. To better determine the shallow slab geometry we depth converted four MCS profiles post-migration. For the range of inferred basement velocities of 5-6.5 km/s the slab dips an average of 7-10 degrees and reaches depths of 18-22 km in the south, 70 km from the trench axis. Serpentinite seamounts on the lower slope of the outer forearc obstruct the slab reflection. A subducting seamount is imaged as an out-of-plane reflection between the trench axis and the southeast flank of Big Blue serpentinite seamount. In areas where water depths are less than 4 km, the slab reflection is also obscured by the seafloor multiple. We used multiple suppression techniques such as Radon Velocity Filter, dip filters, and bottom mutes to enhance the slab reflection. These MCS sections image, for the first time, the geometry of the subducting Pacific Plate beneath the outer Mariana forearc.
DE: 1734 Seismology
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8104 Continental margins: convergent
DE: 8138 Lithospheric flexure
SC: Tectonophysics [T]
MN: Fall Meeting 2005