ACTIVE FAULTING AND QUATERNARY SLIP RATES OF THE COLOMBIAN SUB-ANDES

Abstract

Active deformation of northwestern South America is the result of the complex interaction between the Caribbean and Nazca plates subducting beneath South America, in sharp contrast to the classic Andean-type margin, south of 5° south latitude. This change in plate configuration is reflected in the distribution and kinematics of active structures in the upper plate, where strain is distributed over hundreds of active structures capable of generating damaging earthquakes. To achieve the goal of understanding the distribution and kinematics of active faults, digital archives of active structures are being compiled worldwide. These archives can be used in conjunction with many different tools (e.g. Global Positioning Systems) to estimate the modern slip rates of active faults, which in turn can be used by policy makers to determine better ways to build safer buildings. As an example of recent deformation, and with the aim of comparing recent to millennial scale shortening rates, we analyze in detail the structural evolution of the Tame anticline, located in the Colombian sub-Andes. Here, we use detailed geomorphic and structural analysis from a 300 km2 seismic survey to investigate the relationship between finite shortening and surface uplift and its effects on landscape evolution A quantitative description of finite shortening of the pre-growth strata from line-length and excess area calculations along the fold trend are presented and then compared, as an added check, with the uplift and shortening of geomorphic markers dated using in situ produced Terrestrial Cosmogenic Nuclides (TCN), providing the first estimates of Quaternary shortening along the Northern Colombian Andes at millennial time scales.