| LAFEMINA,
Peter, Division of Marine Geology and Geophysics, University of
Miami - RSMAS, 4600 Rickenbacker Cswy, Miami, FL 33149,
plafemina@rsmas.miami.edu, DIXON, Timothy, RSMAS-MGG, Univ of Miami,
4600 Rickenbacker Causeway, Miami, FL 33149, and GOVERS, Rob, Faculty
of Earth Sciences, Utrecht University, PO Box 80.021, Utrecht, 3508,
Netherlands
We present the first regional surface velocity field for
Central America, showing the crustal response to interaction of the
Cocos and Caribbean plates. Our data show 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. However, large
subduction zone earthquakes occur in Nicaragua (e.g., September 2,
1992, Mw 7.6). We propose that interseismic locking in Nicaragua and
some other parts of Central America is mainly shallow, <20 km depth
(most subduction seismogenic zones extend to ~50 km depth), too far
offshore to be detected by on-land sensors. We present a collision
(rather than subduction) model involving CNS-2 - Cocos Ridge crust;
young, hot-spot thickened 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 southern Costa Rica at rates of ~35 mm yr-1. The
indenter, rather than oblique convergence, drives trench-parallel
forearc motion in Costa Rica and Nicaragua at rates up to 14 mm yr-1.
|