Localization and characterization of an active fault in an urbanized area in central Guatemala by means of geoelectrical imaging |
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| Authors: | Barbara Suski Gilles Brocard Christine Authemayou Beatriz Consenza Muralles Christian Teyssier Klaus Holliger |
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| Institution: | 1. RISKNAT Group, GEOMODELS, Departament de Geodinàmica i Geofísica, Facultat de Geologia, Universitat de Barcelona, c/Martí i Franquès, s/n, 08028 Barcelona, Spain;2. Barcelona Center for Subsurface Imaging (B-CSI), Departament de Geociències Marines - Institut de Ciències del Mar - CSIC, 08003 Barcelona, Spain;3. Institut de Radioprotection et Sûreté Nucléaire - Seismic Hazard Division (BERSSIN), BP 17, 92262 Fontenay-aux-Roses, France;4. Área de Geodinámica Externa, Facultad de CC. Ambientales, Universidad de León, Campus de Vegazana s/n, 24071, León, Spain;5. Departamento de Geodinamica, Universidad Complutense, Instituto de Geociencias IGEO (UCM, CSIC), 28040 Madrid, Spain;6. Department of Geological Sciences, San Diego State University, San Diego, CA 92182, USA;7. Berkeley Geochronology Center, Berkeley, CA 94709, USA;8. Landscape Dynamics, Department of Geography, University of Sheffield, Sheffield S10 2TN, UK;1. Université Grenoble Alpes, CNRS, IRD, IFSTTAR, ISTerre, Grenoble, France;2. Université Savoie Mont Blanc, ISTerre, Chambéry, France;3. Université Blaise Pascal - Clermont-Ferrand II, Clermont-Ferrand, France;4. Hawai''i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai''i at Mānoa, Honolulu, HI, USA;5. Water Resources Research Center, University of Hawai''i at Mānoa, Honolulu, HI, USA;6. Instituto de Investigação em Vulcanologia e Avaliação de Riscos, Universidade dos Açores, Ponta Delgada, Portugal;7. Centro de Informação e Vigilância Sismovulcânica dos Açores, Ponta Delgada, Portugal;8. Sorbonne Universités, UPMC Univ. Paris 06, CNRS, EPHE, UMR 7619 METIS, Paris, France;9. Department of Mining and Metallurgical Engineering, Yazd University, Yazd, Iran;10. Geophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland;11. Géophysique Expérimentale, Institut de Physique de Globe de Strasbourg, UMR 7516 CNRS, Université de Strasbourg/EOST, Strasbourg cedex, France;12. Applied and Exploration Geophysics Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung (ITB), Bandung, Indonesia;13. Center for Volcanology and Geological Hazard Mitigation, Geological Agency of Indonesia, Indonesia;1. Key Laboratory of Seismic Observation and Geophysical Imaging, Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;2. Shandong Institute of Earthquake Engineering, Jinan 250014, China |
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| Abstract: | The Polochic and Motagua faults define the active plate boundary between the North American and Caribbean plates in central Guatemala. A splay of the Polochic Fault traverses the rapidly growing city of San Miguel Uspantán that is periodically affected by destructive earthquakes. This fault splay was located using a 2D electrical resistivity tomography (ERT) survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built. ERT images show the fault as a ~50 m wide, near-vertical low-resistivity anomaly, bounded within a few meters by high resistivity anomalies. Forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location, geometry, and internal structure of the fault zone as well as the affected lithologies. Our results indicate that the city is constructed on a ~20 m thick surficial layer consisting of poorly consolidated, highly porous, water-logged pumice. This soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking. The electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might, at least in part, be fed by water rising along the fault. Therefore, the potential threat posed by this fault splay may not be limited to its seismic activity per se, but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments. The results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of San Miguel Uspantán and illustrate the potential of ERT surveying for paleoseismic studies. |
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