[S22-1] Lithosphere structure and dynamics

[S22-1-02] LITHOSPHERIC STRUCTURE IN THE NORTHWEST SOUTH AMERICA FROM RECEIVER FUNCTIONS ANALYSIS

Carlos Alberto Vargas Jimenez¹, Gaspar Monsalve², Faustino Blanco¹, Esteban Poveda³,^○Marcelo Assumpcao⁴ (1.Universidad Nacional de Colombia at Bogota, 2.Universidad Nacional de Colombia at Medellin, 3.Universidade Federal do Rio Grande do Norte at Natal, Brazil, 4. University of Sao Paulo)

We have combined seismological data of the National Seismological Network of Colombia for estimating the P to S and S to P receiver functions beneath Colombia and adjacent regions to make a first order approximation of the thickness of the crust and the Lithosphere-Asthenosphere Boundary (LAB) in the NW South America. An iterative time-domain deconvolution process was carried out and then a move-out correction with a time-depth conversion using seismograms of distant earthquakes recorded at broadband stations. 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 65 and 110 km, also increasing from NW to SE. Lithospheric thickness beneath an oceanic island in the Caribbean is 80 km, whereas for the Ecuador and Colombia Trench is 65 km and around 100 km for the Panama Arc. The transition to the continent is associated with an increase in LAB depth, where it can reach 110 km, with no significant differences among terranes and tectonic blocks.

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 LAB likely represents the base of the oceanic plate beneath the continental crust. The Caldas tear structure may correspond to the southern limit of this plate, where the Nazca plate, appears to subduct with an angle of 34 degrees. This scenario is also consistent with recent observations of teleseismic travel time residuals, which suggest a relatively cold upper mantle, as well as seismic reflection and gravity data.