The rheological behavior of the lithosphere is examined beneath the Northwestern (NW) Andes (Colombian). Two profiles, one on western and other on eastern of the transition area between the Upper Magdalena Valley (UMV) and the Middle Magdalena Valley (MMV), are obtained from the analysis of the earthquake distribution and the stress drop. Results are consistent with the tectonic and geodynamic context of the western region. In essence, the brittle/ductile transition of the lithospheric crust and mantle is observed, and an approximation of the lithospheric thickness is made. Moreover, the subduction phenomenon of the Nazca Plate under the South American Plate is shown. In the Eastern region, we contemplate an aseismic zone under the Eastern Cordillera below 20 km deep that makes it challenging to know the crust/mantle boundary. This seismic particularity leads us to support the hypothesis of a delamination process due to the tectonic, geological, and thermal context. Our results suggest that the earthquake dataset correlated with rheological estimations may offer a consistent interpretation of the mechanical behavior of the lithosphere.