Effects of Cocos Ridge Collision on the Western Caribbean: Is There a Panama Block?
Open Access
- Author:
- Kobayashi, Daisuke
- Graduate Program:
- Geosciences
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 27, 2012
- Committee Members:
- Peter Christopher Lafemina, Thesis Advisor/Co-Advisor
- Keywords:
- Tectonics
Neotectonics
Geodynamics
GPS Geodesy
Seismic Hazard - Abstract:
- We present improved block kinematics of the western Caribbean and a new interpretation of tectonic behavior of the Panama Region, both of which suggest effects of the Cocos Ridge collision. It has been argued whether the region behaves as a tectonic block, a segmented region, or a deforming zone. This study is the first to comprehensively analyze the kinematics of Central America, using a spatially and temporally reinforced Global Positioning System (GPS) network covering the region from Guatemala to Colombia. Through kinematic block modeling, we simultaneously solve for the Euler vectors of the Central American fore arc, the Panama Region, and the North Andes and Choco blocks in northwestern South America, and coupling on block bounding faults that best describe the observed velocity field. We use seismic reflection profiles, seismic tomography, hypocentral locations, and structural and geologic studies to propose and approximate block boundaries. In our inversion of the three-dimensional GPS velocity data and earthquake slip vectors, published Euler vectors constrain block motion. We construct nine principal models to investigate the location and nature of the western boundary of the Panama Region and to test different block models of the western Caribbean. Model results suggest counterclockwise rotation of the Central American fore arc relative to the Caribbean plate described by the Euler vector, (89.1W, 8.0N, 1.125 ± 0.121° Ma-1), indicating tectonic escape from the Cocos Ridge. The block rate and motion of the fore arc ranges from 10.4 mm a-1 directed northwestward in northern Costa Rica to 15.0 mm a-1 directed westward in Guatemala. In our best-fit model, the Panama Region is a single tectonic block rotating counterclockwise about the Euler pole located at 95.6W, 26.9N and at a rate of 0.216 ± 0.238° Ma-1 relative to the Caribbean plate, not a predictable direction for tectonic escape. We interpret this northeastward motion as a result of ridge collision and northwestward pushing from the neighboring Choco and North Andes blocks. Network gaps in the Panama Region leaves the possibility that a segmented or deforming Panama Region explains the surface velocities better than the single block model. The Panama Region motion in central Costa Rica relative to the Caribbean plate suggests a recurrence interval longer than 420 years for earthquakes comparable to the 1991 MW 7.7 El Limon event along the western segment of the North Panama Deformed Belt. Our coupling results indicate the possibility that a larger strain than that for the 1950 MS 7.7 earthquake has accumulated on the Nicoya segment of the Middle America trench. For the Osa segment, it is possible that sufficient elastic strain has accumulated to cause a 1983 Osa-style (MW 7.4) earthquake.