Abstract
The Otomo rice field zone in Rikuzentakata City, Iwate Prefecture was catastrophically damaged by large-scale subsidence and the tsunami that followed the Great East Japan earthquake, which occurred on March 11th, 2011. Electrical conductivity of underground water, bulk electrical conductivity of the soil, and various meteorological elements were observed at a fixed point for eight months. The electrical conductivity of underground water fluctuated irregularly at the beginning of the observation period, temporarily reaching up to 5 Sm-1 at sea level. After some time, an overall decreasing trend prevailed, and when the observations ended the conductivity of the water had dropped to 0.55 Sm-1. The bulk electrical conductivity of the soil also decreased gradually, from 0.4 to 0.3 Sm-1, over the eight months, which is likely linked to the interactions between rainfall and seawater intrusions. The decrease in soil conductivity has been more gradual here than in the regions affected by the tsunami following the earthquake in the Indian Ocean off Sumatra on December 26th, 2004, and in our study area it has not yet decreased to a level that would allow the resumption of rice farming. It is proposed that this difference is a result of the subsidence in Iwate Prefecture.
Highlights
The fourth largest earthquake in recorded history occurred in the Tohoku region, on the Pacific shore of Japan, on March 11th, 2011
Flooding from the inflow of rain and seawater that originated around the demolished reclamation dyke and subsided areas is frequently seen, representing a particular hydrological phenomenon of the area around the observation point
It is difficult to quantify the inflow of such water, and its extent is demonstrated by the scenes captured by fixed- point photography
Summary
The fourth largest earthquake in recorded history occurred in the Tohoku region, on the Pacific shore of Japan, on March 11th, 2011. The magnitude of this earthquake was 9.0, and its hypocenter was located 70 km off the Oshika peninsula, Miyagi Prefecture [1]. We investigate a rice field zone in Rikuzentakata City, which received considerable damage during the 2011 tsunamis. The Otomo rice field zone in Rikuzentakata City, Iwate Prefecture is located at around 39°N and 142°E, and has a total area of 120 ha, developed behind the reclamation dyke constructed along the Hirota
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