Lagoonal sediments as indicators of coseismic uplift around Acapulco, Mexico
by
Andrew B. Cundy
Centre for Environmental Research, University of Sussex, Brighton, BN1 9QJ, U.K.
Coauthors: A. Carranza-Edwards (Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de México, México D.F., México), M. Frogley (Centre for Environmental Research, University of Sussex, Brighton, BN1 9QJ, U.K.), J. Stone (Centre for Environmental Research, University of Sussex, Brighton, BN1 9QJ, U.K.), L. Rosales-Hoz (Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de México, México D.F., México)

Coastal sediment sequences have been widely used as indicators of past environmental changes, including those associated with catastrophic events such as earthquakes and tsunami. A number of studies have used wetland stratigraphies along tectonically active plate-boundary coastlines (and less active tectonic settings) as indicators of past large- and moderate-magnitude earthquakes (e.g. Nelson et al 1996, Cundy et al 2000). These have typically used detailed lithological studies and macro- or micro-fossil analyses of coastal sedimentary sequences to identify the timing of past major earthquakes, and the magnitude of coseismic and postseismic crustal movements. Much of this work has concentrated on areas subject to coseismic subsidence, but coseismic uplift and rapid relative sea-level fall should also be clearly identifiable in coastal and terrestrial sediment sequences. Here, we assess the usefulness of sediment sequences from tropical coastal lagoons in Guerrero State, Mexico, in identifying and constraining the uplift from large magnitude thrust earthquakes on the Mexican sector of the Pacific continental margin. In particular, the sedimentary signature of the decimetre-scale uplift associated with the 1957 (M 7.7) Acapulco-San Marcos earthquake is examined. Preliminary stratigraphic, radiometric and microfossil studies of sediments from mangrove areas at the rear of the lagoon are presented, and the extent to which the lagoonal sediments and coastal geomorphology show evidence of coseismic uplift is assessed.

References:

Cundy A.B., S.Kortekaas, T.Dewez, I.S.Stewart, P.E.F.Collins, I.W.Croudace, H.Maroukian, D.Papanastassiou, P.Gaki-Papanastassiou, K.Pavlopoulos and A.Dawson. 2000. Coastal wetlands as recorders of earthquake subsidence in the Aegean: a case study of the 1894 Gulf of Atalanti earthquakes, central Greece. Marine Geology, 170, 3-26.

Nelson A.R., Shennan, I. and Long, A.J. 1996. Identifying coseismic subsidence in tidal-wetland Stratigraphical sequences at the Cascadia subduction zone of western North America. J. Geophys. Res., 101: B3, 6115-6135.

Date received: April 19, 2002