HR: 0800h
AN: T41C-0702    [Abstracts]
TI: The seismic structure of the Rivera subduction zone
AU: * Grand, S P
EM: steveg@geo.utexas.edu
AF: University of Texas at Austin, Dept of Geological Sciences, University of Texas at Austin, Austin, TX 78712, United States
AU: Yang, T
EM: tyang@mail.utexas.edu
AF: University of Texas at Austin, Dept of Geological Sciences, University of Texas at Austin, Austin, TX 78712, United States
AU: Wilson, D
EM: davew@geo.utexas.edu
AF: University of Texas at Austin, Dept of Geological Sciences, University of Texas at Austin, Austin, TX 78712, United States
AU: Guzman Speziale, M
EM: guzmarco@hotmail.com
AF: UNAM, Centro de Geociencias Campus Juriquilla, UNAM, Queretero, QRO 76001, Mexico
AU: Gomez Gonzales, J
EM: gomez@geociencias.unam.mx
AF: UNAM, Centro de Geociencias Campus Juriquilla, UNAM, Queretero, QRO 76001, Mexico
AU: Dominguez Reyes, T
EM: tonatiuhdr@hotmail.com
AF: Universidad de Colima, Observatorio Vulcanologico Av Gonzalo de Sandoval 444, Colima, COL 28040, Mexico
AU: Ni, J
EM: jni@NMSU.Edu
AF: New Mexico State University, Department of Physics New Mexico State University, Las Cruces, NM 88003, United States
AB: The subduction zone of western Mexico is a unique region on Earth where microplate capture and overriding plate disruption are occurring today. The small Rivera plate is subducting beneath western most Mexico primarily beneath Jalisco state while to the east it is the Cocos plate that is subducting. Above the Rivera plate the Jalisco block of Mexico is bounded by the north trending Colima Rift and the northwest trending Tepic-Chapala Rift and may form a microplate in its own right. Magmatism is present throughout the region and is unusual for a subduction zone in that geochemical analyses indicate an ocean island basalt component to some of the lavas. Also, Colima volcano is offset trenchward from other volcanoes in the Mexican Volcanic Belt. Little is known of the subducting Rivera plate geometry due to the paucity of seismicity within the plate yet the geometry of the Rivera and Cocos plates at depth are likely critical for understanding the tectonic evolution of western Mexico. The MARS (MApping the Rivera Subduction zone) project consists of the deployment of 50 broadband seismometers covering the Jalisco block from the coast to the Tepic-Chapala rift in the north and about 150 km to the west of the Colima rift. The instruments were deployed in January, 2006 and removed in June, 2007. The goal of the project is to seismically image the subducting Rivera and Cocos plates at depth as well as the mantle wedge above the plates. We present the results of a P-wave tomography inversion using teleseisms recorded by MARS. The inversion used 10,495 residuals and finite frequency theory to back project the kernels through the model. At shallow depths it is difficult to discern the subducting Cocos and Rivera plates but at depths deeper than about 80 km both plates are clearly imaged in the tomography model. Below a depth of 150 km, a clear gap between the Rivera and Cocos slabs is apparent that increases in size at further depths. The images indicate that the deeper Rivera plate is subducting more steeply than the adjacent Cocos plate and also has a more northerly trajection. The break between the two plates is just to the west of Colima graben. The Rivera and western most Cocos plates reach depths exceeding 200 km to the south of the main Mexican Volcanic Belt. The Rivera plate is at roughly 140 km depth beneath the young (<3Ma) central Jalisco Volcanic lineament indicating the Rivera plate has likely recently rolled back and steepened.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1207 Transient deformation (6924, 7230, 7240)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting