KATSETSIADOU, K.-N., ANDREADAKIS,E., LEKKAS, E. (2014). – Ishinomaki Tsunami Intensity Mapping (ITIS2012) for the 9Mw Tohoku Event, March 11 2011, Japan. International Workshop on Mega Earthquakes and Tsunamis in Subduction Zones: Forecasting Approaches and Implications for Hazard Assessment, Rhodes.
The study applies the Integrated Tsunami Intensity Scale1 (ITIS2012) criteria to map the tsunami intensities distribution in the broader Ishinomaki area, for the 9Mw March 11, 2011 event offshore Tohoku, Japan. Reports, satellite imagery and published point and zone data were taken into account to rank the impact of the tsunami in each of the six criteria categories of the ITI Scale. Impact of all categories was mapped on city blocks, point measurements, findings etc, so that thematic impact maps were first created. Then intensity values were assigned, depending on the impact for each category to produce thematic tsunami intensity maps (layers). Most of the criteria result in a mosaic of intensities, which is in many cases due to lack of data, depending on the land use zoning. The complementary function of the criteria is evident in the final map. Two different methodologies of criteria combination were used for the production of a final map. A land-use-based weighted overlay was applied integrating the layers of the criteria, resulting in a final map that rather shows damage assessment or total impact of the tsunami on Ishinomaki area. The second final map was produced using the cell statistics "max" function, so that the maximum grade throughout the layers was selected for each pixel. This map showed an excellent zoning filling in any gaps due to lack of information in some layers and areas with maximum intensity data from the others and it is the tsunami intensity map of the area. It was made very clear though, that field data, especially during the first hours or days after such an event, are extremely useful for the intensity assessment. Once restoration works begin, it is difficult to estimate impact for some categories, especially when the area has been hit by both earthquake and tsunami.