Characteristics of shoreline retreat due to the 2011 Tohoku earthquake and Tsunami and its recovery after three years

Abstract

We investigate the characteristics of shoreline retreat due to the 2011 Tohoku Earthquake and Tsunami and its recovery after 3 years over a wide area from Aomori Prefecture to Ibaraki Prefecture by analyzing the data of crustal deformation, tsunami height, and aerial photographs. There were no significant retreats where the seawall remained unbreached and where river mouths were distantly located regardless of the tsunami overflow depth over the seawall, indicating that the seawall condition during tsunami strikes is one of the most important factors that prevent serious shoreline retreat. After 3 years from the event, recovery of the eroded Ria coasts has been insignificant compared to the plain coasts. The key natural factors for the recovery are the upward crustal deformation after the earthquake and sediment supply from adjacent coasts or rivers after the tsunami; however, these could not be expected at the Ria coasts at least in near future.