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| | Abstract | | The author has conducted integrated geophysical investigations for levee systems at 47 sites, 77 stages since 2005. Among them, a levee which had been attacked by the 2011 off the pacific coast Tohoku Earthquake, has been repeatedly monitored. The levee is a 2 km long section of the left bank of Kokai River, flowing nearby our Institute situated in the south region of Ibaraki Prefecture. We can correlate a total of 5 resistivity profiles obtained by using OhmMapper, and 3 S-wave velocity profiles reconstructed from Land Streamer surface wave survey data. As a result, resistivities along the levee significantly increased after the earthquake, and gradually decreased to the original condition. In contrast, S-wave velocities seem to have recovered from low values in most portions caused by the earthquake. The result suggests that we have to take account of not only transient responses to water infiltration but also seismic effects for the safety assessment of levee systems. |
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