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Title: Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles

Abstract

In the northern Gulf of Alaska and Prince William Sound, wide-angle seismic reflection/refraction profiling, earthquake studies, and laboratory measurements of physical properties are used to determine the geometry of the Prince William and Yakutat terranes, and the subducting Pacific plate. In this complex region, the Yakutat terrane is underthrust beneath the Prince William terrane, and both terranes are interpreted to be underlain by the Pacific plate. Wide-angle seismic reflection/refraction profiles recorded along 5 seismic lines are used to unravel this terrane geometry. Modeled velocities in the upper crust of the Prince William terrane (to 18-km depth) agree closely with laboratory velocity measurements of Orca Group phyllites and quartzofeldspathic graywackes (the chief components of the Prince William terrane) to hydrostatic pressures as high as 600 MPa (6 KBAR). An interpretation consistent with these data extends the Prince William terrane to at least 18-km depth. A landward dipping reflection at depths of 16--24 km is interpreted as the base of the Prince William terrane. This reflector corresponds to the top of the Wadati-Benioff zone seismicity and is interpreted as the megathrust. Beneath this reflector is a 6.9-km/s refractor, that is strongly reflective and magnetic, and is interpreted to be gabbro in Eocenemore » age oceanic crust of the underthrust Yakutat terrane. Both wide-angle seismic and magnetic anomaly data indicate that the Yakutat terrane has been underthrust beneath the Prince William terrane for at least a few hundred kilometers. Wide-angle seismic data are consistent with a 9 to 10[degree] landward dip of the subducting Pacific plate, distinctly different from the inferred average 3 to 4[degree] dip of the overlying 6.9-km/s refractor and Wadati-Benioff seismic zone. The preferred interpretation of the geophysical data is that one composite plate, composed of the Pacific and Yakutat plates, is subducting beneath southern Alaska.« less

Authors:
; ; ; ; ;  [1];  [2]
  1. (Geological Survey, Menlo Park, CA (United States))
  2. (Purdue Univ., West Lafayette, IN (United States). Dept. of Earth and Atmospheric Sciences)
Publication Date:
OSTI Identifier:
5342827
Alternate Identifier(s):
OSTI ID: 5342827
Report Number(s):
CONF-9305259--
Journal ID: ISSN 0016-7592; CODEN: GAAPBC
Resource Type:
Conference
Journal Name:
Geological Society of America, Abstracts with Programs; (United States)
Additional Journal Information:
Journal Volume: 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; Journal ID: ISSN 0016-7592
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GEOLOGIC FAULTS; SEISMIC SURVEYS; GULF OF ALASKA; SUBDUCTION ZONES; DATA ANALYSIS; GEOMETRY; MAPPING; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; GEOPHYSICAL SURVEYS; MATHEMATICS; PACIFIC OCEAN; SEAS; SURFACE WATERS; SURVEYS 580000* -- Geosciences

Citation Formats

Brocher, T.M., Fuis, G.S., Fisher, M.A., Plafker, G., Moses, M.J., Taber, J.J., and Christensen, N.I.. Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles. United States: N. p., 1993. Web.
Brocher, T.M., Fuis, G.S., Fisher, M.A., Plafker, G., Moses, M.J., Taber, J.J., & Christensen, N.I.. Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles. United States.
Brocher, T.M., Fuis, G.S., Fisher, M.A., Plafker, G., Moses, M.J., Taber, J.J., and Christensen, N.I.. Thu . "Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles". United States.
@article{osti_5342827,
title = {Mapping the megathrust beneath the northern Gulf of Alaska using wide-angle seismic reflection/refraction profiles},
author = {Brocher, T.M. and Fuis, G.S. and Fisher, M.A. and Plafker, G. and Moses, M.J. and Taber, J.J. and Christensen, N.I.},
abstractNote = {In the northern Gulf of Alaska and Prince William Sound, wide-angle seismic reflection/refraction profiling, earthquake studies, and laboratory measurements of physical properties are used to determine the geometry of the Prince William and Yakutat terranes, and the subducting Pacific plate. In this complex region, the Yakutat terrane is underthrust beneath the Prince William terrane, and both terranes are interpreted to be underlain by the Pacific plate. Wide-angle seismic reflection/refraction profiles recorded along 5 seismic lines are used to unravel this terrane geometry. Modeled velocities in the upper crust of the Prince William terrane (to 18-km depth) agree closely with laboratory velocity measurements of Orca Group phyllites and quartzofeldspathic graywackes (the chief components of the Prince William terrane) to hydrostatic pressures as high as 600 MPa (6 KBAR). An interpretation consistent with these data extends the Prince William terrane to at least 18-km depth. A landward dipping reflection at depths of 16--24 km is interpreted as the base of the Prince William terrane. This reflector corresponds to the top of the Wadati-Benioff zone seismicity and is interpreted as the megathrust. Beneath this reflector is a 6.9-km/s refractor, that is strongly reflective and magnetic, and is interpreted to be gabbro in Eocene age oceanic crust of the underthrust Yakutat terrane. Both wide-angle seismic and magnetic anomaly data indicate that the Yakutat terrane has been underthrust beneath the Prince William terrane for at least a few hundred kilometers. Wide-angle seismic data are consistent with a 9 to 10[degree] landward dip of the subducting Pacific plate, distinctly different from the inferred average 3 to 4[degree] dip of the overlying 6.9-km/s refractor and Wadati-Benioff seismic zone. The preferred interpretation of the geophysical data is that one composite plate, composed of the Pacific and Yakutat plates, is subducting beneath southern Alaska.},
doi = {},
journal = {Geological Society of America, Abstracts with Programs; (United States)},
issn = {0016-7592},
number = ,
volume = 25:5,
place = {United States},
year = {1993},
month = {4}
}

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