3:30 PM - 4:45 PM
[MIS11-P09] Preliminary GPR study on the effects of topography on the preservation of paleotsunami deposits
Keywords:paleotsunami deposits, paleo-topography, GPR
Given the recognized control of deposit preservation/thickness imparted by the contemporary paleo-topography it is preferable to obtain as much information about subsurface structures as possible during the early stages of any research project in order to more effectively identify the appropriate study sites for ongoing work. In this study we report on a Ground Penetrating Radar (GPR) survey carried out on Ishinomaki plain to help clarify the relationship between paleo-topography and tsunami deposit preservation/thickness. GPR transects were measured along 10 profiles within a 50 × 30 m grid. The non-invasive data collected by GPR was validated by studying the deposits preserved in a series of trenches or cores taken at each transect intersection point. Using these data we recreated the three-dimensional paleo-topography dated to around 3,000~3,500 yr ago that currently underlies the contemporary peat surface throughout the study area. This reconstruction included the spatial distribution and thickness of tsunami deposits, beach ridges and peat sequence.
In summary, we found that tsunami deposits were well preserved/thicker where they are associated with paleo-topographic depressions, and are overlain by a relatively thick peat sequence. Conversely, the peat is thin and tsunami deposits are either non-existent or difficult to distinguish from beach ridge deposits when associated with paleo-topographic highs. While this work in essence concurs with findings from historical events, it highlights the value of GPR surveys for identifying the best paleotsunami study sites based upon an understanding of subsurface paleo-topography. This will greatly enhance the success of future paleotsunami fieldwork.