Tsunami sediments occurred on the March 2011 Tohoku-Oki Earthquake in coastal ponds and lakes

We surveyed tsunami sediments in the seven coastal ponds and lakes along Chiba to Miyagi Prefecture. These ponds and lakes were attacked by large tsunami wave occurred the 11 March Tohoku-Oki Earthquake (Mw 9.0). Measured tsunami height of these area changes from 5 to 12 meters (The 2011 Tohoku Earthquake Tsunami Joint Survey Group). Thickness of tsunami sediment of these pond and lakes ranges from 3 to 20 centimeters in average. The Agawa-Numa Pond elongates 800 meters length from the coast to the land. Tsunami sediments of the nearest shoreside sample consist of granule sized conglomerate and coarse shell sand at base, grade to fine sand bed having over 20 cm in thickness. The landside sample which locates away 1.3 km from shore line contain 7cm layer of well mixed sandy mud. These results are useful to reconstruct past tsunami height from sediments which are found in ponds and lakes along the another subduction zone, such as Nankai Trough.