HR: 14:55h
AN: G22D-06    [PDF]
TI: Sea Level Changes and Active Tectonics of the Guerrero Coast, Mexico
AU: * Ramirez-Herrera, M
EM: ramirezt@csulb.edu
AF: Geological Sciences, California State University Long Beach, 1250 Bellflower Blv., Long Beach, CA 90840 United States
AU: Cundy, A B
EM: A.B.Cundy@sussex.ac.uk
AF: Centre for Environmental Research,, University of Sussex, Brighton, BN1 9RH United Kingdom
AU: Sedor, M
EM: SedorM@aol.com
AF: Geological Sciences, California State University Long Beach, 1250 Bellflower Blv., Long Beach, CA 90840 United States
AU: Kostoglodov, V
EM: vladi@servidor.unam.mx
AF: Instituto de Geofisica, UNAM, Circuito de la Investigacion, CU, Mexico, 01000 Mexico
AB: Understanding the interaction between sea-level changes and tectonic activity during the Holocene is essential in determining long-term tectonic deformation rates and in identifying prehistorical earthquake events along active margins. The Guerrero coast extends along the active Pacific margin of southwest Mexico and parallels the trench where the Cocos Plate subducts beneath the North American Plate. The last major earthquakes occurred in Guerrero in 1899, 1907, 1909, 1911, and 1957, but none have occurred since the major 1911 (Ms=7.6) earthquake in the northwest segment of the Guerrero seismic gap. The Guerrero gap is currently considered to be matured for a severe earthquake of estimated Mw= 8.1 to 8.4. We present preliminary results of geomorphic field surveying, sediment coring, and geochemical and microfaunal analyses of cored sediments on the Guerrero coast. The Coyuca lagoon strip of the Guerrero coast consists of long barrier beaches, behind which extends a lagoon, beach ridges, extensive swamps, mangrove swamps, salt pans, floodplains, alluvial plains, fluvial terraces, and abandoned meanders. Abandoned meanders and fluvial terraces indicate that the Coyuca River has migrated to the southeast. This migration, and changes in hill elevations near the coast, suggest a southeast tilting of this coastal segment. The morphology of the Guerrero coast has no evidence of long-term coastal uplift. This is consistent with short- term tide gauge measurements (1953-1999) and GPS data (1992-2000) indicative of subsidence rates of ~3 mm/yr (Kostoglodov et al., 2001) in this area. Five cores up to 5.5 m depth were taken nearby the Mitla, Coyuca, Tres Palos and Tecomate lagoons. Core stratigraphies show clear sequences of interbedded peats and clays, interspersed with sand units. The peat-clay sequences are similar to those observed along active margins elsewhere, and indicate fluctuations between marine and brackish/freshwater conditions. Two cores included sediments with archeological remains (pottery). The stratigraphic data, coupled with geomorphic evidence, indicate changes in relative sea-level associated with long-term tectonic deformation. On-going radiocarbon dating of shells and charcoal, and detailed geochemical and micro-faunal (i.e. pollen, ostracod and foraminiferal) analyses are being used to constrain the timing and confirm the nature of these sea-level change events.
UR: http://seis.natsci.csulb.edu/tramirez/tramirez.html
DE: 1824 Geomorphology (1625)
DE: 4556 Sea level variations
DE: 4564 Tsunamis and storm surges
DE: 7221 Paleoseismology
DE: 8107 Continental neotectonics
SC: Geodesy [G]
MN: 2003 Fall Meeting