LITHOSPHERIC STRUCTURE IN THE NORTHWEST SOUTH AMERICA: CONSTRAINING THE PROBLEM WITH RECEIVER FUNCTIONS AND OTHER GEOPHYSICAL OBSERVATIONS

Recent receiver function results put new constraints on the lithospheric structure of the NW South America. This seismological technique looks for phase conversions across major boundaries, which represent impedance contrasts, in order to estimate their depths. An iterative time-domain deconvolution process was carried out, using seismograms of distant earthquakes recorded at broad-band stations of the National Seismological Network of Colombia. P-to-S receiver functions reveal a relatively thin crust in northern Colombia, with a thickness that roughly varies between 25 and 39 km, with an increase from NW to SE. S-to-P receiver functions were used to estimate lithospheric thickness, yielding values between 93 and 134 km, also increasing from NW to SE. These results are consistent with the ideas of flat subduction beneath the Colombian Caribbean coast, where a relatively thin continental crust, which gradually thickens toward the SE, is on top of a shallowly subducting Caribbean Plate; the obtained lithosphere - asthenosphere boundary likely represents the base of the oceanic plate beneath the continental crust. The Caldas tear structure (Vargas and Mann, 2013) may correspond to the southern limit of this plate, where the Nazca plate, appears to subduct with an angle of 34º. This scenario is also consistent with recent observations of teleseismic travel time residuals (Yarce et al., 2014), which suggest a relatively cold upper mantle, as well as seismic reflection (Bernal-Olaya et al., 2014) and gravity data (Bernal-Olaya, 2014; Sanchez-Rojas and Palma, 2014).