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CONTROL ID: 1806557 TITLE: Paleoseismological History of the Acambay Graben (Central Mexico) AUTHORS (FIRST NAME, LAST NAME): Pierre Lacan1, Ramón Zúñiga1, María Ortuño1, 2, Mira Persaud1, 3, Gerardo J Aguirre-Diaz1, Robert M Langridge4, Pilar Villamor4, Héctor Perea5, Petra Štěpančíková6, Dora Carreon1, Mariano Cerca1, Iván Suñe Puchol1, Ona Corominas Calvet1, 2, Laurence Audin7, Stéphane Baize8, Timothy F Lawton1, Albeiro Rendón9 INSTITUTIONS (ALL): 1. Centro de Geociencias, UNAM National Autonomous University of Mexico, Juriquilla, Querétaro, Mexico. 2. Dept. de Geodinàmica i Geofísica, Universitat de Barcelona, Barcelona, Spain. 3. OMV Exploration & Production GmbH, Vienna, Austria. 4. GNS Science, Lower Hutt, New Zealand. 5. Barcelona-CSI, Institut de Ciències del Mar - CSIC, Barcelona, Spain. 6. Department of Engineering Geology and Geofactors, Institute of Rock Structure and Mechanics, Academy of Sciences, Praha, Czech Republic. 7. Institut des Sciences de la Terre, ISTerre, IRD, Université Joseph Fourier, Grenoble, France. 8. Seismic Hazard Division, Institute of Radiological Protection and Nuclear Safety (IRSN), Fontenayaux-Roses, France. 9. Facultad de Minas, Universidad Nacional de Colombia, Medellín, Colombia. ABSTRACT BODY: The Acambay graben is part of the Trans-Mexican Volcanic Belt (TMVB) which strikes ESE-WNW across central Mexico, where the major part of the Mexican population is concentrated. The TMVB is an active, calc-alkaline volcanic arc that is related to the subduction of the Rivera and Cocos plates underneath the North American plate. The TMVB contains a series of intra-arc basins that form the Chapala-Tula fault zone (450 km long, 50 km wide). One of these extensive basins, the Acambay graben, is 80 km long and 15 to 30 km wide. It is limited north by the E-W striking Epitacio-Huerta (EHF) and Acambay-Tixmadejé normal faults and south by the Venta de Bravo (VBF) and the Pastores faults (PF) in the south. Other minor active faults are located within the basin, along the axis of the Graben. In the area, the instrumental seismicity is low to moderate, although one major historical earthquake (Ms = 6.9 Acambay event) occurred on November 19, 1912, causing widespread damage. In the last decade, our group has focused on the neotectonic and paleoseismological study of the major faults of the Acambay graben. More than 30 trenches have been dug at 15 sites in order to interpret the paleoseismological history of 7 major faults of the graben. In addition to paleoseismological trench studies, tectonic geomorphology, subsurface geophysics and micro topographic surveys have been used to assess the rupture history. All of the studied faults have to be considered as active faults, with a minimum of 2 to 5 paleoseismic events on each fault during the last 20 ka. Each fault rupture corresponds to a vertical displacement ranging from 1 to 150 centimetres. Considering the size of the observed displacements and the length of active segments, we demonstrate that large earthquakes with magnitude higher than 7 have occurred along some of these faults. Based on paleoseismological results, we calculate a major earthquake recurrence interval ranging from 2,000 to 5,000 years over a time span (~20 ka). These recurrence values overpass the Mexican historical seismicity catalogue that incorporates no more than the last 500 years. This suggests that most of the faults of the TMVB may be active despite the lack of known historical destructive events and could be able to produce earthquakes with serious consequences in the most populated area of Mexico.
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KEYWORDS: 8107 TECTONOPHYSICS Continental neotectonics, 7221 SEISMOLOGY Paleoseismology, 8109 TECTONOPHYSICS Continental tectonics: extensional, 4302 NATURAL HAZARDS Geological. (No Image Selected) (No Table Selected) Additional Details Previously Presented Material: Contact Details CONTACT (NAME ONLY): Pierre Lacan CONTACT (E-MAIL ONLY):
[email protected] TITLE OF TEAM: PALEOSISMEX
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