Is there a Tsunami flood area forecast map?


Question:

Preparing M (Magnitude) 8 class aftershock, is there a Tsunami flood area forecast map for Iwate, Miyagi, and Fukushima Prefecture? (Female, 40s, Miyagi)

Answer:

Aftershocks bigger than M5 have occurred more than 430 times after the 2011 Tohoku Earthquake (as of May 1). We cannot foresee when and where tsunami will strike after bigger aftershocks. Since the east coast of Tohoku has been on an earthquake high alert, disaster prevention maps, including possible tsunami floods appeared on some communities’ homepages.

Higashi-Matsushima City, Miyagi Pre. – “Prevention Map” (Only Japanese)
Matsushima Town, Miyagi Pre. – “Tsunami flood area forecast Map” (Only Japanese)

These prevention maps were created based upon data from past disasters. Indeed, those maps estimate a large earthquake as that of the Miyagiken-oki Earthquake (about M8.2) in 1793. The earthquake on March 11, however, was beyond any projections.

Although we heard many times “no one foresaw such an earthquake,” which was true, people still presumed the past should prevent future disasters. This is of note in that most of the historical roads and post-towns of southern Miyagi Prefecture were not flooded in March 2011. Thus, some areas might have learned by past events, but no one could predict or prepare for the March 11 experience.

The Geospatial Information Authority of Japan (GSI) released the conspectus maps of flooded area investigated to be 561 km2 (0.7 of Sendai City or 9 times of Yamanote rail circuit).

The GSI acquired satellite images and aerial photographs along with topographic and geological data such as tsunami deposits and faults, and rainfall analysis from maximum rainfall records. The GSI correlated all that data to create maps projecting potential flood areas to help avoid future disasters.

No more to say “it was not presumed”, better prepared tsunami flood projections can help people better prepare and would be the key for recovery.


Science Communicator: Yuko Okayama