Measurements of upper mantle shear wave anisotropy from a permanent network in southern Mexico |
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Authors: | Steven AC van Benthem Raúl W Valenzuela Gustavo J Ponce |
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Institution: | Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands;Departamento de Sismología, Instituto de Geofísica, Universidad Nacional Autónoma de México Mexico D.F., México;Departamento de Sismología, Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación S/N, Cd. Universitaria, Del. Coyoacán, 04510. México, D.F., México;Departamento de Sismología, Instituto de Geofísica, Universidad Nacional Autónoma de México, Circuito de la Investigación S/N, Cd. Universitaria, Del. Coyoacán, 04510. México, D.F., México;Departamento de Geofísica, Facultad de Ingeniería, Universidad Nacional Autónoma de México, Mexico D.F., México |
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Abstract: | Upper mantle shear wave anisotropy under stations in southern Mexico was measured using records of SKS phases. Fast polarization directions where the Cocos plate subducts subhorizontally are oriented in the direction of the relative motion between the Cocos and North American plates, and are trench-perpendicular. This pattern is interpreted as subslab entrained flow, and is similar to that observed at the Cascadia subduction zone. Earlier studies have pointed out that both regions have in common the young age of the subducting lithosphere. Changes in the orientation of the fast axes are observed where the subducting plates change dip and/or are torn, and are thus indicative of 3-D flow around the slab edges. They are consistent with slab rollback, as previously shown by other authors. Some stations located away from the plate boundaries have their fast directions controlled by the absolute motion of the North American plate. The fast axis for station ZAIG, located in the Mesa Central, is oriented WNW-ESE and is different from all the other measurements in this study. |
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Keywords: | anisotropía del manto superior flujo del manto zonas de subducción Fosa Mesoamericana placas de Cocos Rivera y América del Norte upper mantle anisotropy mantle flow subduction zones Middle America Trench Cocos Rivera North American plates |
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