Changes in elements and magnetic properties of Sendai Bay sediments caused by the 2011 Tohoku‐oki tsunami

• Published in: The island arc Vol. 31; no. 1
• Main Authors: Abe, Hirokuni, Kawamura, Noriko, Ishikawa, Naoto, Kogiso, Tetsu
• Format: Journal Article
• Language: English
• Published: Melbourne John Wiley & Sons Australia, Ltd 01-01-2022; Wiley Subscription Services, Inc
• Subjects: 2011 Tohoku‐oki tsunami; Copper; Earthquakes; Flooding; Hurricanes; Island arcs; Magnetic permeability; Magnetic properties; Magnetic susceptibility; Magnetite; Marine sediments; Metal concentrations; Metals; Nitrogen; Organic carbon; Organic matter; Remanent magnetization; Sediment; Sediment samplers; Sediment samples; Sediments; Seismic activity; Sendai Bay; Sulfur; Sulphur; Titanium; Total organic carbon; tsunami deposit; Tsunamis; Typhoons; Zinc
• ISSN: 1038-4871; 1440-1738
• DOI: 10.1111/iar.12437

Nearshore marine sediments deposited along island arcs can preserve evidence of past disaster events, such as tsunamis. Evidence of a tsunami that occurred off the Pacific coast of Tohoku, Japan, on March 11, 2011, was likely preserved in marine sediments. Using geochemical and rock magnetic analyses, this study aimed to investigate tsunami records preserved in marine sediments in Sendai Bay, located west of the epicenter of the 2011 Tohoku earthquake. We collected sediment samples at five stations (S‐1, S‐2, S‐3, S‐4, and S‐5) in Sendai Bay from 2002 to 2014. We compared the samples collected before and after the tsunami. We established that the silt component increased, while that of fine sand decreased at stations S‐3, S‐4, and S‐5 in the 2011 sediment sample. Notably, the concentrations of terrestrial and industrial metallic elements (Cu, Zn, and Pb) and total nitrogen, carbon, and sulfur amounts increased, while the magnetic susceptibility and isothermal remanent magnetization values decreased after the tsunami. We also found that Ti‐poor magnetite increased in the 2011 samples, indicating tsunami‐mediated changes. The study area experienced a large typhoon 6 months after the tsunami, leading to flooding. The elevation in the total organic carbon and total nitrogen ratio in the 2012 sample suggested that terrestrial organic matter was supplied by the flood.