Morphometry of late Pleistocene-Holocene faulting and volcanotectonic relationship in the southern Andes of Colombia

Diffuse seismicity and the active Galeras Volcano characterize the southern Andes of Colombia, whose inhabitants are prone to a high natural risk. We used field geological, structural, and quantitative morphological data to d efine the geometry and kinematics of late Quaternary faults and the volcano tectonic relationships in this area. The main NE-SW Buesaco Fault has a lat e Pleistocene-Holocene 29-km rupture length. Offset of dated landforms yiel ds 188 +/- 13 m of horizontal, right-lateral, longterm cumulative component of slip, the vertical component of uplift of the NW block being 67 +/- 12 m. The long-term net slip rare is 1.48 +/- 0.12 mm/yr. The other main struc ture, here named Aranda Fault, also strikes NE-SW and is 13 lan long. Offse t of landforms yields 160 +/- 10 m of horizontal, right-lateral. long term component of slip and 3.9 +/- 1.9 m of vertical component of uplift of the NW block. The long-term net slip rate is 1.19 +/- 0.08 mm/yr. On the Galera s edifice E-W to NW-SE faults have normal motions and slip rates from 0.02 to 0.23 mm/yr. Both the Galeras and a late Pleistocene pyroclastic cone lie along the ideal extension of the Buesaco Fault. Magma uprising in the crus t can occur along the NE striking fractures when magma pressure (sigma mp) is greater than the normal-to-fault component of tectonic sigma 1. Magma up rising in the uppermost crust (i.e., in the cone) can occur by rock crackin g along E-W planes with sigma mp > sigma 3 up to NW-SE planes with sigma mp greater than shear stress component of the horizontal greatest principal s tress (sigma(Hmax))