Interactions between active tectonics and gravitational deformation along the Billecocha fault system (Northern Ecuador): Insights from morphological and paleoseismological investigations

Autor: Stéphane Baize, Benjamin Bernard, D. Saqui, Monica Segovia, Alexandra Alvarado, D. A. Pacheco, Silvana Hidalgo, Hervé Jomard, Laurence Audin, Mario Ruiz
Přispěvatelé: PSE-ENV/SCAN/BERSSIN, Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Instituto Geofisico - Escuela Politecnica Nacional (IGEPN), Escuela Politécnica Nacional (EPN), Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA), Géoazur (GEOAZUR 7329), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [France-Sud]), Bureau d'évaluation des risques sismiques pour la sûreté des installations (IRSN/PSE-ENV/SCAN/BERSSIN), Service de caractérisation des sites et des aléas naturels (IRSN/PSE-ENV/SCAN), Institut de Radioprotection et de Sûreté Nucléaire (IRSN)-Institut de Radioprotection et de Sûreté Nucléaire (IRSN)
Jazyk: angličtina
Rok vydání: 2021
Předmět:
Zdroj: Journal of South American Earth Sciences
Journal of South American Earth Sciences, Elsevier, 2021, 111, pp.103406. ⟨10.1016/j.jsames.2021.103406⟩
Journal of South American Earth Sciences, 2021, 111, pp.103406. ⟨10.1016/j.jsames.2021.103406⟩
ISSN: 0895-9811
Popis: International audience; The Billecocha plateau (4000 m a.s.l.) lies in the high elevation Ecuadorian Andes volcanic arc. It overhangs by 2000 m above the interandean valley. Both the plateau and surrounding volcanoes are heavily affected by active faulting characterized by straight, sharp and discontinuous scarps within a 6 km wide and 24 km long corridor. Contrasting interpretations have been proposed to explain the expression at surface of the so-called Billecocha fault system (BFS), from normal faulting related to postglacial elastic rebound or gravitational processes, to right-lateral faulting compatible with the North-Andean Sliver tectonic regime. The instrumental seismicity recorded around the BFS is low, however, a M~7 earthquake heavily struck the region in 1868.With the aim to discuss the kinematic and coseismic nature of the encountered deformations as well as the seismogenic character of the BFS, we performed (1) morphological analysis to map and quantify evidence of active faulting and (2) paleoseismological investigations across the longer segment of the fault system. In three trenches, we show that surface deformations are at least partly coseismic in origin during the Holocene with a minor lateral component, the last paleoseismic event being compatible in date with the 1868 earthquake. In addition, some of the enlightened paleoseismic events could have occurred in relationship with volcanic eruptions of the surrounding volcanoes.While field evidence of reverse and strike slip faulting suggests that regional tectonics could be involved, the geomorphological signature of the BFS at the mountain scale, as seen on the digital surface model, can partly be related to the development of deep seated gravitational deformations, hence suggesting an interaction between boundary (i.e. tectonic, volcanic) and body forces (i.e. gravity, post-glacial rebound). Further studies are however mandatory to better address the influence of each process at the BFS, in particular geodetic and seismological surveys.Given the available data, we suggest that the BFS could actually correspond to the distributed surface expression of the tectonic reactivation of the inherited Pujilí suture, enhanced by gravitational phenomenon. In this light, paleoearthquakes identified along the BFS may help evidencing the recurrence of major events in the region. However, it also imply that surface deformations along the BFS shall not be used without a careful and more detailed field work to derive fault slip rates for seismic hazard calculations.
Databáze: OpenAIRE
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