Résumé
We present initial remote sensing and field data that suggest active distributed right-lateral faulting at the northern edge of the Quito-Latacunga tectonic block in northern Ecuador and southern Colombia. In this region, oblique subduction of the Nazca Plate beneath the South America plate induces northward migration of the Northern Andean Sliver (NAS), with respect to stable South America. Recent geodetic studies now suggest that this sliver is composed of several independent tectonic blocks, and the boundaries of these blocks are locations where we hypothesize crustal strain is accommodated. One of these blocks, the Quito-Latacunga block, is located in the densely populated Interandean valley of northern Ecuador and southern Colombia, and geodetic modelling predicts approximately 3 mm/yr of right-lateral strain at its northern boundary. A shallow July 25, 2022, MW 5.6 earthquake and damaging historical earthquakes along the northern boundary have illustrated the importance of understanding where this strain is being accommodated. We use available digital surface models (DSMs), local DSMs derived from Pleiades and SPOT satellite stereo-imagery, Interferometric Synthetic Aperture Radar (InSAR), Google Earth imagery, and a field survey to show that this boundary is distributed across several parallel northeast striking right-lateral faults. InSAR shows the July 25 event resulted in right-lateral surface displacement of > 20 cm along an east-northeast striking, steeply dipping fault. Offset volcanic soils and glacial moraines indicate recent earthquakes on two faults north of and subparallel with this rupture. Both faults overlap with the proposed area for the August 15, 1868, M 6.4-6.8 El Angel earthquake, suggesting either fault could be associated with this event. As the DSMs reveal a number of parallel strike-slip faults to the north in Colombia, further paleoseismic studies are needed in this region to delineate active faults and help define regional seismic hazard.