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Seafloor Geodesy: Transitioning to continuous measurements of plate motion in subduction zones. Dave Chadwell (email@example.com) Scripps Institution of Oceanography. With thanks to: H. Fujimoto, M. Fujita , K. Gagnon , M. Kido, Y. Matsumoto, Y. Osada, K. Tadokoro. Outline.
Dave Chadwell (firstname.lastname@example.org)
Scripps Institution of Oceanography
With thanks to: H. Fujimoto, M. Fujita , K. Gagnon , M. Kido, Y. Matsumoto,
Y. Osada, K. Tadokoro
Question: Where is the locked zone?
Approach: Assume elastic strain = f(convergence rate, fault geometry, lock zone). Observe elastic strain on continent with land-based geodetics, convergence rate from far-field GPS or geology, assume or solve-for thrust fault geometry, and solve for the lock zone:
1 . No deformation measurement in the submerged up-dip region.
2. No direct geodetic observation of convergence adjacent to the subduction zone.
A need for seafloor geodesy …..
Direct path (0-2 km)
Indirect Direct path
(e.g., Sweeney et al., 2005,
(e.g., Chadwell et al.,1999, GRL)
(e.g., Spiess et al., 1998, PEPI)
Northern Cascadia:(Spiess et al., 1998, PEPI)
Japan Trench: (Osada et al., 2006)
Central Cascadia: (Chadwell et al., in prep) “non-uniform”
Interseismic and Coseimic :
Peru: (Gagnon, Chadwell, Norabuena, 2005, Nature)
Japan Trench: (Fujita et al., 2006; Matsumoto et al., 2006)
Nankai Trough: (Kido et al., 2006; Tadokoro et al., 2006)
(e.g., Phillips et al.,2008, JGR)
Mid-Ocean Ridge inflation:
Axial Volcano:(Chadwick et al., 2006, J. Vol. Geoth. Res.)
South Flank Kilauea Volcano : (Phillips, Chadwell, Hildebrand, 2008, JGR)
Observations: Each Node interrogates (20x) all transponders for the two-way travel time
Unknowns: Local east, north position of node and east, north and up position of transponder
Goal: Daily cm-level
Chadwell-SIO/ BP America Inc.
(not to scale)
M. Mochizuki, A. Asada, T. Ura（Univ. of Tokyo）
M. Fujita, M. Sato, Y. Matsumoto （Japan Coast Guard）
O. L. Colombo （NASA）
T. Tanaka, Z. Hong （SEA Corp.）
K. Nagahashi（MES Co., Ltd.）
Tryon &Brown capture ambient pressure at deployment, thermally isolated reference; system about to be deployed with buoy.
Sasagawa & Zumberge use a “dead” weight that is “raised’’ to preset height by a generated pressure that forms the reference; bench test completed.
NS-OTIC 3-year project started 1/1/07, Brown, Chadwell, Send, Tryon at SIO to build a horizontal (GPSA) and vertical (pressure) sensor. Deployed in August 2008 for initial multi-month test offshore San Diego.
Vertical: drift-controlled pressure w/ water density, surface pressure, and surface height measured
Horizontal: GPS-Acoustic measurements every 60 seconds.