The thickness of the seismogenic crust (Ts) controls crustal earthquakes. Its upper limit is the seismicity onset depth (SOD) while its base corresponds to the seismicity cutoff depth (SCD) that correlates with the brittle-ductile transition. Thus, it influences the magnitude and location of crustal earthquakes and knowledge of its geometry may aid in seismic hazard assessment. Here we present the first Ts map of the Andean margin. We follow the standard methodology using the statistical depth distribution of events on a grid of equally size square cells. However, we find it has flaws and develop a new approach, based on circular cells of variable radius that changes according to earthquake density. Our results indicate that Ts is heterogenous, showing three controls: thermal structure, subduction geometry and crustal thickness.