| Title | Geometry and membrane deformation rate of the subducting Cascadia slab |
| Download | Download (whole publication) |
| |
| Licence | Please note the adoption of the Open Government Licence - Canada
supersedes any previous licences. |
| Author | Chiao, L -Y; Creager, K C |
| Source | The Cascadia subduction zone and related subduction systems - seismic structure, intraslab earthquakes and processes, and earthquake hazards; by Kirby, S (ed.); Wang, K (ed.); Dunlop, S (ed.); Geological Survey of Canada, Open File 4350, 2002 p.
47-54, https://doi.org/10.4095/222496  Open Access |
| Links | Online - En ligne
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| Year | 2002 |
| Alt Series | United States Geological Survey, Open-file Report 02-328 |
| Publisher | Natural Resources Canada |
| Meeting | Intraslab Earthquakes in the Cascadia Subduction System: Science and Hazards; Victoria; CA; September 18-21, 2000 |
| Document | open file |
| Lang. | English |
| Media | on-line; digital |
| Related | This publication is contained in The Cascadia subduction
zone and related subduction systems - seismic structure, intraslab earthquakes and processes, and earthquake hazards |
| File format | pdf |
| Province | Western offshore region |
| NTS | 92A; 92B |
| Area | Georgia Strait; Puget Sound; Juan de Fuca Sound; United States of America; Canada |
| Lat/Long WENS | -126.0000 -122.0000 49.0000 47.0000 |
| Subjects | tectonics; structural geology; geophysics; subduction zones; plate tectonics; tectonic elements; tectonic environments; tectonic interpretations; plate motions; subduction; lithosphere; oceanic
lithosphere; deformation; geometric analyses; kinematic analysis; modelling; rheology; Cascadia Subduction Zone; Cascadia Margin; Juan de Fuca Plate; Juan de Fuca Slab; Mendocino Transform; SHIPS; Cenozoic |
| Illustrations | tables; sketch maps |
| Released | 2002 06 11; 2016 08 31 |
| Abstract | The Juan de Fuca plate subducts along the west coast of North America along a plate boundary that extends some 1000 km from northern California to Vancouver Island. In map view, the plate boundary is
nearly straight along its northern and southern regions, but exhibits a 35°
change in orientation offshore from northern Washington State. Landward from this bend is an arch in the shape of the subducting plate, a concentration in Wadati - Benioff
seismicity and an anomalously thick Miocene accretionary prism that makes up the two kilometer-high Olympic Mountains. We speculate that all three are related, directly or indirectly, to the fact that the Cascadia slab is subducting into a concave,
oceanward corner which creates a geometric space problem analogous to pleats in a tablecloth hanging off the corner of a table. To test this hypothesis, we develop a theory of steady state, incompressible three-dimensional fluid flow that is
asymptotically valid for a thin slab with high linear (or non-linear) viscosity relative to the surrounding fluid. Flow in this simple model is constrained by kinematic boundary conditions rather than buoyancy forces. Fixing the slab geometry to the
same trench-normal profile along the entire subduction
zone, we invert for the flow field that minimizes the dissipation power of the system and find that strain rates, characterized by along-strike compression, are concentrated along the west
coast of Washington, reaching values of 2x10-16 s-1. In a second experiment, we constrain
the same 20° dip along the northern and southern edges of the subducting plate and find that the optimal slab geometry contains an arch in a location similar
to the seismologically observed arch, and that the root-mean square of the strain rates are reduced by a factor of five.
Thus, if these strain rates are accommodated by intraplate earthquakes, this arching model provides a geometry that allows a
five-fold reduction in seismic moment release rates. The predicted strain rates are consistent with the observed moment release rate associated with one Mw=7 and several Mw>6 earthquakes per century in the Olympic Mountain/Puget Sound region, and a
much lower rate to the north and south. Predicted strain rates associated with slab bending and unbending are generally smaller than the predicted membrane strain rates. The anomalously thick accretionary prism associated with the Olympic Mountains
can be explained by the critical taper theory as being caused by the shallow dip of the slab along the arch. |
| GEOSCAN ID | 222496 |
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