Date of Award

Fall 12-2020

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Ocean Science and Engineering

Committee Chair

Davin Wallace

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Jessica Pilarczyk

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Mustafa Kemal Cambazoglu

Committee Member 3 School

Ocean Science and Engineering

Abstract

The 2011 Tohoku tsunami impacted the northeastern coast of Japan and caused unexpected damages due to the underestimation of this type of hazard. Of particular importance is the fact that geologic evidence for a predecessor event, the Jogan tsunami (CE 869), could have forecasted the severity of the 2011 Tohoku event. While the timing of tsunamis is important for effective hazard mitigation, outside of the 2011 Tohoku event, the intensity of past tsunamis remains unclear. To understand paleotsunami intensity, it is important to document characteristics of modern analogues like the 2011 event. This study utilizes surface distributions of foraminifera from coastal and offshore locations within Sendai Bay to determine the provenance for 2011 Tohoku tsunami sediments preserved within rice fields on the Sendai Plain near the towns of Yamamoto, Shinchi, and Suijin-numa. We use foraminiferal taxonomy and taphonomy to characterize surface sediments from various locations in and around Sendai Bay as well as the 2011 Tohoku tsunami sediments. The taxonomic and taphonomic assemblages of the 2011 tsunami sediments are similar to that of the intertidal zone, indicating that the dominant sediment source was from locations within 300 m of the coastline. PAM (partitioning around medoids) cluster analysis further provided evidence of a coastal to nearshore sediment source as it clustered the 2011 Tohoku tsunami sediment within intertidal biofacies. By understanding the provenance of a known modern analogue, this technique may be useful to future studies that aim to investigate the relative intensity of tsunamis preserved in the geological record.

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