Mapping Tsunami Inundation Areas on the Pacific Coast of Hokkaido
- AIST's Contribution to Disaster Prevention through Geological Survey and Tsunami Simulation -

( Translation of the AIST press released on March 29, 2005)

Key Points

Inundation areas affected by a giant tsunami on the Pacific Coast of Eastern Hokkaido triggered by a great earthquake in the 17th century have been plotted on a topographic map.
The tsunami data caused by the 2003 Tokachi-oki Earthquake are compared with those for the tsunami triggered by the great earthquake striking the Pacific Coast of Eastern Hokkaido in the 17th century.
A more effective disaster prevention plan may be drafted by using the data as basic material for the preparation of the regional disaster prevention plan of Hokkaido.

Synopsis

The Active Fault Research Center (AFRC) and the Institute of Geology and Geoinformation (IGG) of the National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institution, have compiled the"Tsunami Inundation Maps for the Pacific Coast of Hokkaido", to be designated as "Inundation Maps" hereinafter.

The AFRC/IGG-AIST has been investigating records of past earthquakes for the purpose of long-term forecast of great earthquakes at active faults and submarine trenches around Japan. The Inundation Maps have been compiled on the basis of geological survey and tsunami simulation for the Pacific Coast of Eastern Hokkaido, having been carried out as a part of these efforts. The Maps contain data of devastating tsunami from a gigantic earthquake caused by multi-segment interplate rupture at the Kuril Subduction Zone in 17th century and struck the Pacific Coast of Eastern Hokkaido, as well as those of another destructive tsunami accompanying the 2003 Tokachi-oki Earthquake.

The Maps have made it possible to estimate the peak height of the tsunami striking the Pacific Coast of Eastern Hokkaido caused by the giant earthquake in the 17th century, and to compare them with the data of the recent tsunami associated with the 2003 Tokachi-oki Earthquake. In the Maps, detailed data of flooded area, flood depth and maximum flow rate are plotted for 5 localities.

Certain local communities are currently preparing their own regional disaster prevention plans. The Inundation Maps are expected to be helpful as a basic material for revising the plan. In this way, it will become possible to predict the potential damages to be caused by a massive tsunami which may occur in the future on the basis of data of tsunami in the past, ensuring drafting of more effective forecast of damages caused by possible giant tsunami in the future. Besides, these attempts will serve as a reference for drafting a tsunami hazard map in areas other than Hokkaido.

The AFRC/IGG-AIST is going to investigate deposits and geological structures off the Pacific Coast of Hokkaido and along the Kuril Subduction Zone for the purpose of long-term forecast of great earthquake originating from the zone, and to extend the survey to tsunami deposits along the Pacific Coast beyond Hokkaido. Moreover, it is planned to carry out the survey of tsunami deposits at Off-Chile and Off-Sumatra.

The Inundation Maps have been published in the form of a CD-ROM, which will be available at an authorized dealer[1].

Fig. 1 A typical representation of the Inundation Maps for the Pacific Coast of Hokkaido: comparison of arrival time and wave height of the tsunamis caused by the giant earthquake in the 17th century and by the 2003 Tokachi-oki Earthquake, at five points: Nambu-numa, Nemuro; Kiritappu, Hamanaka; Tokotan-numa, Akkeshi; Pashukuru-numa, Onbetsu; and Oikamanai-numa, Taiki.

Background

The AFRC/IGG-AIST has been investigating geologic records of past earthquakes for the purpose of long-term forecast of great earthquakes to occur at active faults and submarine trenches around Japan. As a part of these efforts, geological traces of earthquakes, tsunamis and crustal movements in the past along the Pacific Coast of Eastern Hokkaido have been investigated since 1997.

History of Research Work

Historical records of Eastern Hokkaido are available only from the beginning of the 19th century (around 1800), and data for earthquakes and tsunamis having occurred before that have to resort to geological survey and research. In fiscal year 2003 it was found that a giant, multi-segment, interplate earthquake occurred at the Kuril Subduction Zone off the eastern Hokkaido and induced a massive tsunami in the 17th century (AIST Press Release, August 7, 2003).

Details of Research Work

The AFRC/IGG-AIST has created an inundation map of tsunami-flooded areas on the Pacific Coast of Eastern Hokkaido on the basis of tsunami deposit survey having been carried out up to now, and tsunami simulation based on a fault model.

In the inundation map, variations in tsunami arrival time and peak height caused by a giant multi-segment interplate earthquake in the 17th century and those data of tsunami caused by the 2003 Tokachi-oki Earthquake are plotted on a topographical map on the Pacific Coast of Eastern Hokkaido between Nemuro and Urakawa, together with the distribution of tsunami deposits, maximum water level and maximum flow rate at five places: Nambu-numa, Nemuro; Kiritappu, Hamanaka; Tokotan-numa, Akkeshi; Pashukuru-numa, Onbetsu; and Oikamanai-numa, Taiki.

Besides, crustal movements on the sea bottom and on the coast caused by the 2003 Tokachi-oki Earthquake and the giant earthquake resulting from a multi-segment interplate rupture in the 17th century are illustrated on the basis of a fault model, and some of fault parameters are listed.

Additionally, one may view an animated graphics of inundation by tsunami at the Kiritappu Wetland, Hamanaka.

Future Prospects

[1] "Tsunami Inundation Maps of the Pacific Coast of Hokkaido", Digital Geologic Map Series: EQ-1, Geological Survey of Japan.