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Distributed faulting and hidden seismic hazards at the Ecuador-Colombia border
An international team of geoscientists from ISTerre (CNRS/Université Grenoble Alpes), the University of Alaska Anchorage, and other partner institutions investigated the active fault systems accommodating tectonic strain at the northern edge of the Quito-Latacunga microblock in the high Andes of Ecuador and Colombia.
(a-d) Coseismic deformation during the 25 July 2022 earthquake. Sentinel-1 and ALOS-2 unwrapped interferograms mapping the localized surface displacements and identifying the active rupture trace.
(e) Orthophotomosaics and trench logging of the Reservoir fault. The exposure reveals vertical offsets in post-glacial sediments and organic-rich Andisols, documenting at least three major Holocene earthquakes.
(f-h) Profiles of the Line-of-Sight coseismic displacement from the ALOS-2 unwrapped interferogram (see (d) for profile locations). Blue and red numbers indicates the total amount of deformation and the offset at the surface rupture.
The boundary between tectonic microblocks in this region has long been challenging to map, with geodetic models suggesting approximately 3 mm/year of right-lateral strain. However, the exact structures responsible for this deformation remained unclear. By combining high-resolution digital terrain models (DTMs) from Pleiades satellite stereo-imagery, InSAR data, and rigorous field surveys, the researchers demonstrated that the deformation is not confined to a single large fault. Instead, it is distributed across an up-to 70-km-wide zone of several parallel, northeast-striking right-lateral faults.
The study highlights the active nature of these fault systems. InSAR analysis of a recent July 2022 (Mw 5.6) earthquake revealed clear line-of-sight displacements of 5 to 13 cm along one of these newly characterized faults. Further north, offset glacial moraines and streams along the nearby Reservoir and Polylepis faults show long-term evidence of right-lateral movement. Using cosmogenic 3He surface exposure dating of glacial boulders and radiocarbon dating of organic-rich paramo soils, the team constrained the ages of the displaced landforms and estimated fault slip rates.
Excavations across the Reservoir fault exposed a detailed paleoseismic record, revealing evidence of at least three large, surface-rupturing Holocene earthquakes with estimated magnitudes between Mw 6.3 and 7.0. The mapped active faults overlap with the epicentral region of the devastating 1868 El Angel earthquake (Mw 6.4–6.8), suggesting these structures are capable of hosting highly destructive events.
Beyond localized seismic hazard assessments, the findings suggest that ongoing magmatic inflation at the nearby Chiles-Cerro Negro volcanic complex may influence regional stress fields, potentially enhancing fault slip rates and triggering earthquakes. This study provides a vital framework for understanding how strain is partitioned across mechanically complex tectonic boundaries and emphasizes the hidden seismic risks in densely populated volcanic regions.
The study highlights the active nature of these fault systems. InSAR analysis of a recent July 2022 (Mw 5.6) earthquake revealed clear line-of-sight displacements of 5 to 13 cm along one of these newly characterized faults. Further north, offset glacial moraines and streams along the nearby Reservoir and Polylepis faults show long-term evidence of right-lateral movement. Using cosmogenic 3He surface exposure dating of glacial boulders and radiocarbon dating of organic-rich paramo soils, the team constrained the ages of the displaced landforms and estimated fault slip rates.
Excavations across the Reservoir fault exposed a detailed paleoseismic record, revealing evidence of at least three large, surface-rupturing Holocene earthquakes with estimated magnitudes between Mw 6.3 and 7.0. The mapped active faults overlap with the epicentral region of the devastating 1868 El Angel earthquake (Mw 6.4–6.8), suggesting these structures are capable of hosting highly destructive events.
Beyond localized seismic hazard assessments, the findings suggest that ongoing magmatic inflation at the nearby Chiles-Cerro Negro volcanic complex may influence regional stress fields, potentially enhancing fault slip rates and triggering earthquakes. This study provides a vital framework for understanding how strain is partitioned across mechanically complex tectonic boundaries and emphasizes the hidden seismic risks in densely populated volcanic regions.
The full study is published in : Solid Earth
Fundings : Centre National d’Etudes Spatiales (CNES), Institut de Recherche pour le Développement (IRD), and the Autorité de Sûreté Nucléaire et de Radioprotection (ASNR).
Fundings : Centre National d’Etudes Spatiales (CNES), Institut de Recherche pour le Développement (IRD), and the Autorité de Sûreté Nucléaire et de Radioprotection (ASNR).
References :
Harrichhausen, N., Marconato, L., Audin, L., Lacan, P., Baize, S., Jomard, H., Alvarado, A., Hollingsworth, J., Blard, P.-H., Mothes, P. A., Rolandone, F., and Ortiz Martin, I. D. (2026). Distributed right-lateral strain at the northern boundary of the Quito-Latacunga microblock. Solid Earth, 17, 763-787.
Scientific contacts :
- Laurence Audin – ISTerre, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, Grenoble, France
- Léo Marconato – ISTerre, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, Univ. Gustave Eiffel, Grenoble, France