HR: 11:35h
AN: T42B-06    [Abstracts]
TI: Geomorphic and Geophysical Studies in the Atirro-R\'{i}o Sucio Fault System and the Turrialba-Iraz\'{u} Pull-Apart Basin, Central Costa Rica
AU: * Montero, W
EM: wmontero@geologia.ucr.ac.cr
AF: Escuela Centroamericana de Geolog\'{i}a, Red Sismol\'{o}gica Nacional (ICE-UCR), Apdo 2-14, Universidad de Costa Rica, San Jos\'{e}, 2060 Costa Rica
AU: Kruse, S
EM: skruse@cas.usf.edu
AF: Department of Geology, University of South Florida, 4202 East Fowler Ave. , Tampa, FL 33620 United States
AB: The northwest-striking Atirro-R\'{i}o Sucio fault system and the associated Turrialba-Iraz\'{u} pull-apart basin in central Costa Rica lie in the region separating the northwestern part of the Panama microplate and the Caribbean Plate. These features reflect part of the regional response to the N-NE directed collision of the Cocos Ridge with the Panama microplate in southeastern Costa Rica. The neotectonic Atirro-R\'{i}o Sucio fault system consists of the dextral-slip Atirro, Turrialba, Tucurrique, Lara faults, central and eastern R\'{i}o Sucio faults, and the predominantly normal Azul, Campano, Chiz, and western R\'{i}o Sucio faults. Left steps in the southeast part of this fault system have formed transpressive zones, a few kilometers in width, in the Rinc\'{o}n de la Esperanza, Mirador and Matama areas. These transpressive zones form part of the complex southeastern end of the Turrialba-Iraz\'{u} pull-apart basin, a 40-km (NW-SE) by 10-15 km (NE-SW) zone formed in a right step between the Atirro fault to the southeast and the R\'{i}o Sucio fault to the northwest. The Azul and R\'{i}o Sucio faults mark the northeastern limit of the pull-apart; the southwestern margin is less well defined. Within this zone, significant Quaternary alluvial and lahar deposits have accumulted in the Turrialba, Juray, and Atirro basins. Magnetic anomalies of 500 nT or more coincide with the Azul, Chiz, and Turrialba faults, suggesting structural discontinuities that coincide with the scarps. The Quaternary Iraz\'{u} volcano formed within the west-central portion of the pull-apart; the Turrialba volcano close to the northeast boundary. In this zone thick volcanic deposits have obscured the geomorphic expression of the pull-apart basin. However, the overall N-S trend of the Iraz\'{u} volcanic complex and a group of monogenetic cones within the basin is compatible with formation under tensional stresses associated with pull-apart development. Historical seismicity in the Atirro-R\'{i}o Sucio fault system and the Turrialba-Iraz\'{u} pull-apart includes both swarms and several earthquakes with magnitude greater than 5.0, notably the Patillos event of December 30 1952 (Ms 5.7) and the Pejibaye sequence of July 1993 (magnitudes 5.5 and 5.3).
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting