<p>Building 3-D regional velocity models of complex seismotectonics settings remains challenging; strong heterogeneities, resulting from plate interactions, are difficult to resolve and the lack of well constrained moment tensor solutions for the set of earthquakes used as sources makes model convergence difficult or altogether impossible. We propose a joint velocity and moment tensor elastic full waveform inversion framework in the time domain, to find a solution for P-wave and the complete Moment Tensor (MT) of the seismic sources. We synthetically validate our approach using an upscaled version of the SEAM 3-D velocity model, a standard validation test in exploration seismology known for its strong heterogeneities and velocity contrasts. Our approach shows promising results when applied to the tectonic setting of the Middle Magdalena Valley (MMV) basin, a region known for the poorly understood geometry of the underlying subducting plates. As sources we use intermediate depth earthquakes from the Bucaramanga Seismic Nest (BSN), one of the most compact and active seismicity volumes in the world. As a result, we obtain a 3-D velocity model for the region and a set of well constrained MT solutions for moderate BSN earthquakes. Our framework can be readily applied to other regions and it will be of special importance in applications dominated by moderate seismicity (Mw&lt;5.5), where very few global MT solutions are available.</p>