Active tectonics and earthquake geology along the Pallatanga Fault, Central Andes of Ecuador
| Main Authors: | Stéphane Baize, Laurence Audin, Alexandra Alvarado, Hervé Jomard, Mathilde Bablon, Johann Champenois, Pedro Espin, Pablo Samaniego, Xavier Quidelleur, Jean-Luc Le Pennec |
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| Format: | info publication-preprint |
| Terbitan: |
, 2020
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/3715638 |
Daftar Isi:
- These files are the preprint version of a publication in review to Frontiers in Earth Science, Special Issue "Unveiling Active Faults: Multiscale Perspectives and Alternative Approaches Addressing the Seismic Hazard Challenge by Topic Editors Federica Ferrarini, Ramon Arrowsmith, Michele M. C. Carafa, Nathan Toke. You find the text file, the Supplementary material text and figures in a .zip folder. Additional files (pictures, strip maps, table of observation points coordinates, shapefiles) to the Supplementary material are available here: zenodo.org/record/3706207#.XnMZ96hKjIU Based on new geological data and the analysis of Digital Elevation Model (DEM), we provide a detailed and comprehensive description of a major active fault system in Ecuador. This work allows estimating new slip rates and large earthquakes parameters (displacement, recurrence) along the ~100 km-long section of the continental-scale dextral shear zone that accommodates the extrusion of the North Andean Sliver with respect to the South America continental Plate. We focus on the NE-SW Pallatanga strike-slip fault zone and related contraction features that extend to the north of the previously studied segment, in the Inter-Andean valley. The detailed analysis of the 4m-spatial resolution DEM available for Ecuador allowed mapping a series of lineaments at the regional scale and all along the fault system. Field studies on key areas show geomorphic, valley deflections, aligned and elongated hills of Tertiary or Quaternary sediments, as well as faulted Holocene deposits and even preserved coseismic free-face ruptures in some places. Such morphological anomalies strongly suggest that those landscape scars represent long-living (Holocene to historical times) earthquake faults. Altogether, this new data confirm that very large shallow earthquakes (M~7.5) have been generated along the fault system, probably during multiple segment ruptures. This conclusion is reinforced by the occurrence, during historical times (post 1532 CE) of large earthquakes (1698, 1797 and 1949) in the vicinity of the fault trace during post-Spaniards to modern times, whose effects on environmental and cultural features were reported as catastrophic by historical chronicles. Based on new sample dating of both soils and volcanic series, we infer that the NE-SW dextral Pallatanga fault slips at rates ranging from ~2 to ~6 mm/yr for southern and central strands, respectively. Further north, surface faulting is distributed and the deformation appears to be partitioned between sub-meridian fault-related folds (~2 mm/yr) and NE-SW strike-slip fault(s), like the ~1 mm/yr Pisayambo Fault that ruptured the surface in 2010. All this information offers the opportunity to size the earthquake sources for further seismic hazard analyses.
- Field work expenses have been funded by the "Laboratoire Mixte International Séismes et Volcans des Andes du Nord" of "Institut pour la Recherche et le Développement" (LMI-SVAN), by the "Agence Nationale pour la Recherche" project ANR-REMAKE (N°ANR-15-CE04-0004), and by proper funds from the "Institut de Radioprotection et Sûreté Nucléaire".