Historical tsunami deposits in Peru: Sedimentology, inverse modeling and optically stimulated luminescence dating

摘要

The entire coast of Peru was surveyed to document deposits of historical tsunami. Evidence of four tsunami was found. At Puerto Casma, in northern Peru, a graded, heavy mineral-rich layer with shell- and rock fragments was detected. OSL dating revealed an age of 0.37 ± 0.03 ka (1615-1667 AD). Inverse modelling of tsunami onshore flow parameters indicates a flow depth of ～6 m and a flow speed of ～8 m/s at a distance of ～60 m from the shoreline. For the Chimbote earthquake of 1619 AD, a tsunami was not listed in the historical tsunami catalogues, although it is seen as a predecessor of the 1996 Chimbote earthquake and tsunami. Hence, this study may provide the first evidence of a local tsunami triggered by this event. A graded, shell-rich event layer that contains cobbles with attached marine organisms was found at Vila Vila in southern Peru. This layer was dated to 0.17 ± 0.04 ka (1797-1871 AD) and is most probably the result of the 1868 Arica tsunami. Two additional event layers found in Boca del Rio (southern Peru) were dated 226 ± 0.37 ka (615 BC-119 AD) and 1.98 ± 0.23 ka (207 BC-255 AD). Thus, the layers record for the first time tsunami much older than the events listed in tsunami catalogues. These two events exhibit similar parameters with flow speeds of 7-8 m/s and depths of 6 m in a distance of 460 m from the present shoreline. The time that passed between the events is similar to the recurrence interval of the two Arica tsunami of 1604 and 1868 AD, hence giving evidence of another prehistoric earthquake and tsunami couplet.