Geologic and geodetic observations of active orogenic wedge deformation across the southern Subandes of Bolivia Abstract

abstract

  • Orogenic wedges are fundamental features associated with mountain building yet we are limited in our ability to relate long-term, whole-wedge evolution to deformation processes acting over seismotectonic and decadal timescales. In an effort to bridge this gap we present a new GPS-derived surface velocity field for the central Andean backarc, which includes the ~500-km-long fold-and-thrust belt comprising the southern Subandes of Bolivia (SSAB), combined with the first detailed constraints on the temporal and spatial distribution of recent SSAB wedge-front deformation. Our analysis of stratigraphic relationships across fault-related folds and displacement fields of subsurface seismic reflection horizons indicates that nearly all of the whole-wedge shortening rate determined for the Quaternary Period is absorbed across the frontal thrust fault system. Fault slip rates are generally higher across the younger, northern portion of the fault system where a swarm of earthquakes including 2 magnitude 4.5-5.0 events and associated aftershocks struck the wedge front in October 2013. Wedge-front-perpendicular horizontal surface velocities also vary along strike. In the south, where the wedge is broad and gently tapered, velocities decrease linearly from ~12.8-17.6 mm/yr on the Altiplano to ~0 mm/yr on the adjacent lowlands over a distance of ~500 km. In contrast, a sharp decrease in velocities from ~10 mm/yr to ~0 mm/yr over a distance of ~125 km characterizes the steep and narrow northern wedge. Similar along-strike variations have not been documented in other active wedges and may relate to differences in the underlying d├ęcollement geometry, rate of erosion, or stage of the wedge accretion cycle. Our results for the SSAB aid in and demonstrate some of the difficulties associated with integrating observations over multiple timescales across active orogenic wedges.

publication date

  • 2014

presented at event