2003 Seattle Annual Meeting (November 2–5, 2003)

Paper No. 9
Presentation Time: 3:45 PM


PETERS, Robert B.1, JAFFE, Bruce E.1, GELFENBAUM, Guy2, RUBIN, David M.1, ANIMA, Roberto2, SWENSSON, Matt3, OLCESE, Daniel4, ANTICONA, Luis Bernales4, GOMEZ, Juan Carlos5 and RIEGA, Percy Colque6, (1)USGS Pacific Sci Ctr, 1156 High Street, Santa Cruz, CA 95064, (2)U. S. Geol Survey, 345 Middlefield Road, MS999, Menlo Park, CA 94025, (3)USC, Los Angeles, CA 90089, (4)Dirección de Hidrografía y Navegación de la Marina de Guerra del Perú, Lima, Peru, (5)Instituto Geofísico del Perú, Lima, Peru, (6)Universidad San Agustín, Perú, Arequipa, Peru, rpeters@usgs.gov

Investigating sedimentary deposits from tsunamis shortly after their occurrence can aid in the identification and interpretation of tsunami deposits preserved in the geologic record. By documenting sedimentary characteristics typical of tsunami deposits we can improve our understanding of tsunami depositional processes.

On June 23, 2001, an earthquake centered off the coast of Peru, moment magnitude 8.4, generated a tsunami that inundated more than 50 km of the Peruvian coast in the vicinity of Camana. A field investigation was conducted in September 2001 by a team of scientists from the United States and Peru. Six sites were studied to determine the presence of tsunami deposits, their distribution and sedimentary characteristics. Deposits were identifiable at all six sites using a combination of characteristics. Deposits were most easily identifiable where there was a sharp contrast between the underlying material and the tsunami deposit, such as tsunami deposited beach sand overlying river deposits or agricultural fields. Tsunami sediments deposited directly on beach sand were more difficult to identify. Deposits consisted of sand with a minor proportion of silt. Cobbles and mud rip-up clasts were sometimes present within the deposit or at the surface. At most locations, the deposit contained multiple layers. When present, 2-3 layers were typical, though up to 8 layers were observed at one site. Layers of sand were separated by a thin layer of mud or heavy minerals and often were normally graded. A thin mud cap was sometimes present at the surface. Deposit thickness ranged from 0.5 to 28 cm, thinning landward. Basal contacts were typically erosional. Run-up elevation ranged from 3.0 m to 8.2 m. Tsunami deposits were found up to 490 meters inland extending to within a few meters of the limit of inundation. The field observations and measurements made after the 2001 Peru tsunami are being used to develop criteria for the identification and interpretation of both modern and paleo-tsunami deposits.