Journal
GEOPHYSICAL RESEARCH LETTERS
Volume 41, Issue 24, Pages 8775-8783Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014GL061958
Keywords
SKS splitting; Colombia; anisotropy
Categories
Funding
- NSF-EAR Postdoctoral Fellowship [1249776]
- NSF-EAR [1215720]
- Directorate For Geosciences
- Division Of Earth Sciences [1249776, 1215720] Funding Source: National Science Foundation
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The Nazca, Caribbean, and South America plates meet in northwestern South America where the northern end of the Andean volcanic arc and Wadati-Benioff zone seismicity indicate ongoing subduction. However, the termination of Quaternary volcanism at 5.5 degrees N and eastward offset in seismicity underneath Colombia suggest the presence of complex slab geometry. To help link geometry to dynamics, we analyze SKS splitting for 38 broadband stations of the Colombian national network. Measurements of fast polarization axes in western Colombia close to the trench show dominantly trench-perpendicular orientations. Orientations measured at stations in the back arc, farther to the east, however, abruptly change to roughly trench parallel anisotropy. This may indicate along-arc mantle flow, possibly related to the suggested Caldas slab tear, or a lithospheric signature, but smaller-scale variations in anisotropy remain to be explained. Our observations are atypical globally and challenge our understanding of the complexities of subduction zone seismic anisotropy.
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