HR: 0800h
AN: T41C-1219    [Abstracts]
TI: Tear in the subducting slab beneath the southern Mariana Arc: evidence from P-wave tomography
AU: * Miller, M S
EM: meghan.miller@anu.edu.au
AF: The Australian National University, Research School of Earth Science Mills Road, Building 61, Canberra, ACT 0200 Australia
AU: Gorbatov, A
EM: alexei@jamstec.go.jp
AF: IFREE, JAMSTEC, Yokokhama Inst for Earth Science 3173-25, Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Kennett, B L
EM: brian.kennett@anu.edu.au
AF: The Australian National University, Research School of Earth Science Mills Road, Building 61, Canberra, ACT 0200 Australia
AU: Stern, R J
EM: rjstern@utdallas.edu
AF: University of Texas at Dallas, Geoscience Department Box 830688, Richardson, TX 75083 United States
AU: Gvirtzman, Z
EM: zohar@mail.gsi.gov.il
AF: Geological Survey of Israel, 30 Malkhei Yisrael St, Jerusalem, 95501 Israel
AB: Seismic tomography has developed into one of the most effective and significant sources of information in modern geophysical research, specifically in understanding subduction zone dynamics. The Western Pacific convergent margin is a well studied area, but as more data is collected and technology improves further detailed observations and theories are being developed. New tomographic images of the Mariana Arc region have enhanced resolution of gradients and strong variations in wave speeds through the use a three-dimensional ray-tracing inversion algorithm. Although the images obtained from the Mariana arc show relatively low amplitudes of heterogeneity due to the limited number of seismic stations in the area, details of the geometry and morphology of the Pacific Plate subducting beneath the Philippine Sea Plate are visualized in three dimensions with unprecedented detail. The slab has an arcuate shape in depth, similar to the surface expression of the trench axis, and plunges steeply into the lower mantle in the northern and central portion. A markedly different geometry exists south of 14øN where the slab continues to have a steep dip, but is only 200 km in length. Between the two distinct morphologies is a seismic velocity anomaly that we interpret as a tear. This near vertical tear in the slab strikes E-W, is 75-200 km in depth, and has an eastern extent of 145.5øE and continues westward to approximately 143.5øE. We propose three models to explain the formation of the tear: rapid rollback of the Challenger Deep slab segment, the junction of the Pacific and Caroline plates, or the subduction of the Caroline Islands Ridge.
DE: 8180 Tomography
DE: 7230 Seismicity and seismotectonics
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8123 Dynamics, seismotectonics
DE: 7218 Lithosphere and upper mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting