HR: 11:55h
AN: T52A-07 INVITED    [Abstracts]
TI: Interplay of Structure and Sediment Supply May Influence Subduction Zone Rupture Patches and Propagation
AU: * Goldfinger, C
EM: gold@coas.oregonstate.edu
AF: Oregon State University College of Oceanic and Atmospheric Sciences, Ocean Admin Bldg 104, Corvallis, OR 97331, United States
AU: Wang, K
EM: KWang@NRCan.gc.ca
AF: Geologic Survey of Canada, Pacific Geoscience Centre, 9860 West Saanich Rd. Sidney, Sidney, BC V8L 4B2, Canada
AU: Witter, R
EM: rob.witter@dogami.state.or.us
AF: Oregon Department of Geology and Mineral Industries, 313 SW 2nd Street, Suite D, Newport, OR 97365, United States
AU: Baptista, A
EM: baptista@stccmop.org
AF: Oregon Health & Science University, OGI School of Science & Engineering 20000 NW Walker Road, Beaverton, OR 97006, United States
AU: Zhang, Y
EM: yinglong@stccmop.org
AF: Oregon Health & Science University, OGI School of Science & Engineering 20000 NW Walker Road, Beaverton, OR 97006, United States
AU: Priest, G
EM: george.priest@dogami.state.or.us
AF: Oregon Department of Geology and Mineral Industries, 313 SW 2nd Street, Suite D, Newport, OR 97365, United States
AU: Nelson, H
EM: odp@ugr.es
AF: Instituto Andaluz de Ciencias de la Tierra (IACT) CSIC-Univ. de Granada, Campus de Fuentenueva, Granada, 18002, Spain
AU: Morey, A
EM: morey@coas.oregonstate.edu
AF: Oregon State University College of Oceanic and Atmospheric Sciences, Ocean Admin Bldg 104, Corvallis, OR 97331, United States
AU: Johnson, J
EM: joel.johnson@unh.edu
AF: University of New Hampshire, Department of Earth Sciences, 56 College Rd., Durham, NH 03824, United States
AB: The question of whether there are universal controls on the genesis and maintenance of large slip and moment patches along strike on subduction megathrusts has proved remarkably elusive, in part due to the short temporal records we have of these great events around the globe. Many events this century are poorly constrained, and many subduction zones only have one or a few events available for comparison. Long historical records and good structural constraints have made Nankai a leading case for basin centered asperities, yet the recent Sumatra Mw 9.2 rupture models show that slip and moment for the most part avoided basins and was centered under structural highs. In Cascadia, both deformation and tsunami models clearly fit the respective subsidence and runup data better if slip in past events was centered under or did not avoid these highs as opposed to basin centered model. Onshore and offshore paleoseismic evidence from 38 Cascadia earthquakes strongly suggest that structural segmentation plays a role only along the southernmost margin. These data do not provide information on moment or slip distribution, but do effectively constrain rupture lengths. Rupture lengths constrained by the paleoseismic data show that there is no Holocene segmentation for the northern margin, and that southern segments may be controlled by some of the obvious structural boundaries such as the Blanco Fracture zone, and outer arc uplifts and forearc basins. Where resolution is adequate, these data also suggest that ruptures die out into the basins and are linked multi-segment ruptures of structural uplifts, similar to that observed in the 2004 and 2005 earthquakes from Sumatra where outer arc uplifts may mark segment boundaries, high slip patches and initiation points for great earthquakes. The difference between the rupture modes observed for Nankai and Sumatra, and suggested here for Cascadia may be linked to the sediment supply for these systems. Cascadia and Sumatra are both systems where massive submarine fans are accreting to the margin in their northern regions, with incoming sections of 3-4 km thickness that taper southward. These thick sections promote high fluid pressure, but also tend to smooth the plate interface with respect to structures in both the downgoing and upper plates. A smooth plate interface has long been thought to promote long ruptures and high moment release, and so we suspect that northern Cascadia and northern Sumatra may be prone to large ruptures due to the masking of other structures by large influxes of sediment on the subducting plate. By comparison, the relatively thin sediment supply at Nankai may allow these structural boundaries to play a greater role in rupture propagation and moment release. The smaller southern Cascadia ruptures are also consistent with this model, with structural control taking precedence as the sediment supply thins southward.
UR: http://www.activetectonics.coas.oregonstate.edu/
DE: 7221 Paleoseismology (8036)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting