Overlapping slabs: Untangling subduction in NW South America through finite-frequency teleseismic tomography.

Both the Caribbean and Nazca plates subduct beneath northwestern South America. The configuration of the two subducted slabs and the nature of any interaction between them has long been a matter of debate. Based on the location of intermediate-depth seismicity and active and extinct volcanism, as well as on seismic imaging, several different tectonic scenarios have been proposed. In this paper, we use teleseismic data recorded by the Colombian National Network and the temporary CARMA array in Venezuela and Colombia to produce a finite-frequency tomography model for the region. Our results show several distinct subduction segments. Through synthetic tests, we show that our results require a zone of overlap between Nazca and Caribbean subduction north of the "Caldas Tear" as has been proposed by previous studies. Additionally, we find that the Bucaramanga Nest occurs within the Caribbean Plate and coincides with bending of the slab in two planes, where both the strike and the dip of the slab change. We infer that elevated stresses are an important factor in producing the very high rates of seismicity in the nest. • Teleseismic tomography illuminates the geometry of subduction in NW South America. • There is a zone of overlap between Caribbean and Nazca subduction. • The offset at the Caldas Tear corresponds to seismicity in two different slabs. • The Bucaramanga Nest occurs within the Caribbean Plate. [ABSTRACT FROM AUTHOR]