Distributed right-lateral strain at the northern boundary of the Quito-Latacunga microblock

Abstract

Remote sensing and field data suggest distributed right-lateral faulting at the northern edge of the Quito-Latacunga microblock in northern Ecuador and southern Colombia. Off the west coast of Ecuador and Colombia, oblique subduction of the Nazca Plate beneath the South America plate induces NE-motion of the Northern Andean Sliver relative to stable South America. Recent geodetic studies show this sliver comprises several independent microblocks, with strain accommodated at each of their boundaries. The Quito-Latacunga microblock, located in the densely populated Inter-Andean valley, shows approximately 3 mm yr−1 of right-lateral strain at its northern boundary. However, which structures accommodate this deformation is unclear. Using available digital terrain models (DTMs), local DTMs derived from Pleiades satellite stereo-imagery, InSAR, Google Earth imagery, and field surveys, we demonstrate deformation at the northern boundary is distributed across several NE-striking right-lateral faults in Ecuador and Colombia. InSAR shows that a recent 2022 M5.6 earthquake resulted in line-of-sight displacement of 5 to 13 cm along one of the ENE-striking, right-lateral faults. Offset sediments and glacial features indicate recent earthquakes on two other faults (the Reservoir and Polylepis faults) north of and subparallel with this rupture. Displaced glacial landforms along the Reservoir fault show slip rates between 0.8 and 6.1 mm yr−1, suggesting geologic slip rates that could be higher than geodetic ones. Exposures of the Reservoir fault also show evidence for at least three surface rupturing earthquakes with magnitudes between M6.3 and M7.0. Inflation at the nearby Chile-Cerro Negro volcano may influence earthquakes on these faults, enhancing slip and earthquake rates. The Polylepis, Reservoir, and 25 July earthquake faults all overlap with the proposed area for the 15 August 1868, M6.4–6.8 El Angel earthquake, indicating they could be associated with this damaging event.