HR: 17:45h
AN: T44A-08 INVITED    [Abstracts]
TI: Changes in Seismogenic Zone Coupling Along the Middle America Margin?
AU: * LaFemina, P C
EM: plafemina@geosc.psu.edu
AF: Penn State, Dept. of Geosciences 406 Deike Bldg, University, PA 16802, United States
AU: Dixon, T H
EM: tdixon@rsmas.miami.edu
AF: UM-RSMAS, Division of Marine Geology and Geophysics 4600 Rickenbacker Cswy, Miami, FL 33149, United States
AU: Govers, R
EM: govers@geo.uu.nl
AF: Faculty of Earth Sciences, Utrecht University P.O. Box 80.021, Utrecht, 3508 TA, Netherlands
AU: Protti, M
EM: jprotti@una.ac.cr
AF: OVSICORI - UNA, Universidad Nacional Apartado Postal: 2346-3000, Heredia, 2346-3000, Costa Rica
AU: Gonzalez, V
EM: vgonzale@una.ac.cr
AF: OVSICORI - UNA, Universidad Nacional Apartado Postal: 2346-3000, Heredia, 2346-3000, Costa Rica
AB: Subduction of seamounts, aseismic ridges and bathymetric highs leads to subduction erosion, deformation of the forearc and increased coupling within the seismogenic zone. The latter can result in large magnitude earthquakes, deformation of the forearc and potentially collision tectonics. Variability in bathymetry of the Cocos plate offshore the Middle America Trench allows for the investigation of the effects of bathymetric highs on plate coupling. Here, relatively smooth crust formed at the East Pacific Rise subducts along the MAT in Nicaragua and northern Costa Rica, whereas, rough crust formed at the Cocos – Nazca spreading center (CNS-2) and modified by Galapagos hotspot interacts with the margin in central and southern Costa Rica. We present a regional surface velocity field for Central America showing the crustal response to interaction of the Cocos and Caribbean plates, and investigate the degree of plate coupling and long-term implications of seamount and aseismic ridge subduction. The velocity field indicates significant trench-parallel motion for most of the region, including central Costa Rica, where plate convergence is perpendicular to the trench. Interseismic strain accumulation is observed in the outer forearc Nicoya and Osa Peninsulas, but not in the forearc of Nicaragua or central Costa Rica. Large subduction zone earthquakes occur in Nicaragua (e.g., September 2, 1992, Mw 7.6), however there have been no >Mw 7 earthquakes recorded in central Costa Rica. The velocity field is not well fit by a simple model of interseismic elastic strain accumulation. Inboard of Cocos Ridge, southern Costa Rica, velocity vectors are parallel to convergence and up to 44 mm yr^{- 1}. We present a collision (rather than subduction) model involving CNS-2 - Cocos Ridge crust, and compare our model results and geodetic observations to geological and geophysical data for the region. CNS-2 – Cocos Ridge crust resists normal subduction, instead acting as an indenter to the Caribbean plate, driving crustal shortening in central and southern Costa Rica at maximum rates of 35 mm yr^-1 across the fore arc and back arc. The indenter, rather than oblique convergence, drives trench-parallel forearc motion in Costa Rica and Nicaragua at rates up to 14 mm yr^-1. In total, our results indicate the broad effects of seamount and aseismic ridge interaction with the MAT.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 6924 Interferometry (1207, 1209, 1242)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting