Receiver functions and crustal structure of the northwestern Andean region, Colombia

We used the receiver function technique to deduce crustal thickness beneath the northwestern Andean system, using data from the permanent seismic network of Colombia, combined with some of the IRIS and CTBTO stations in Colombia and Ecuador. The estimation of crustal thickness was made using the primary P to s conversion and crustal reverberations. The bulk crustal V-P/V-S ratio was constrained using a crustal thickness versus V-P/V-S stacking method, in addition to estimations using a time to depth conversion technique based on results of a modified Wadati diagram analysis. We observed a wide range of crustal thicknesses, including values around 17km beneath the Malpelo Island on the Pacific Ocean, 20 to 30km at the coastal Pacific and Caribbean plains of Colombia, 25 to 40km beneath the eastern plains and foothills, 35km beneath the Western Cordillera, 45km at the Magdalena River intermountain valley, 52 to 58km under the northern Central Cordillera, and reaching almost 60km beneath some of the volcanoes of the Southern Cordilleran system of Colombia; crustal thickness can be slightly greater than 60km beneath the plateau of the Eastern Cordillera. The values of V-P/V-S are particularly high for some of the stations on the volcanic centers, reaching values above 1.79, probably related to the addition of mafic materials to the lower crust, and in the plateau of the Eastern Cordillera near Bogota, where we speculate about the possibility of crustal seismic anisotropy associated with shear zones.