Earthquakes beneath the Himalayan collision zone occur at depths between near surface and around 100 km below sea level. After relocating earthquakes with two one‐dimensional (1‐D) velocity models, we found a clear bimodal depth distribution for earthquakes in the Himalayas of eastern Nepal and the southern Tibetan Plateau and evidence that some earthquakes originate at upper mantle depths. Seismicity in Nepal shows an accumulation of earthquakes along the front of the Himalayan arc, with a seismic gap between longitudes 87.3°E and 87.7°E. Although upper crustal seismicity along the topographic front of the High Himalaya is consistent with a region of high strain accumulation associated with convergence on the Main Himalayan thrust fault, microearthquakes do not necessarily occur on this fault. Instead, they concentrate in the hanging wall. Seismic activity in the sub‐Himalaya and the Terai Plains is almost exclusively limited to the vicinity of the location of the magnitude 6.5 20 August 1988 Udayapur earthquake, with most of the earthquakes in the lower crust and the upper mantle. Clusters of earthquakes in the Lesser and High Himalayas and south Tibet (Tethyan Himalayas) mark very well defined zones of seismicity at depths between 50 and 100 km, confirming the presence of earthquakes in the upper mantle in the region of continental collision. The occurrence of earthquakes at sub‐Moho depths favors the idea that the continental upper mantle deforms by brittle processes.

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 primaryPtosconversion and crustal reverberations. The bulk crustalV_P/V_Sratio was constrained using a crustal thickness versusV_P/V_Sstacking 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 17 km beneath the Malpelo Island on the Pacific Ocean, 20 to 30 km at the coastal Pacific and Caribbean plains of Colombia, 25 to 40 km beneath the eastern plains and foothills, 35 km beneath the Western Cordillera, 45 km at the Magdalena River intermountain valley, 52 to 58 km under the northern Central Cordillera, and reaching almost 60 km beneath some of the volcanoes of the Southern Cordilleran system of Colombia; crustal thickness can be slightly greater than 60 km beneath the plateau of the Eastern Cordillera. The values ofV_P/V_Sare 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.