5:15 PM - 6:45 PM
[U15-P71] Preliminary investigation of Flooded area in Hegura Island, Wajima City, by the R6 Noto Peninsula Earthquake Tsunami
Keywords:Hegura Island, field survey, flood area, debris
On New Year's Day in 2024, a Mw-7.5 earthquake occurred with its epicenter located on the northern coast of the Noto Peninsula. Subsequently, the earthquake generated a tsunami that caused severe damage to Ishikawa Prefecture and neighboring prefectures. The aftershock area of this earthquake covered a wide span of 150 km, and the exact location of faults responsible for the earthquake and tsunami remains unclear.Following the disaster, various agencies, including the Coastal Engineering Committee of JSCE, conducted investigations in the affected area. These investigations have helped to elucidate the height of tsunami traces, the extent of flooding, and the overall damage situation. While the available information primarily focuses on the coastal areas of the Noto Peninsula, data regarding the remote islands along the path of the tsunami is scarce. However, newspaper reports have confirmed that three residents were present on Hegura Island when the tsunami struck, resulting in damage to fishing port and park facilities located in the coastal lowlands.The tsunami, originating from the northern coast of the Noto Peninsula, propagated in a northwest direction, passing through Hegura Island and Nanatu Islands before reaching the western sea area of the Noto Peninsula due to the influence of complicated bathymetry. Therefore, information regarding the flooded areas and tsunami traces on Hegura Island can provide valuable insights into the presumed source of this tsunami.
During our participation in the recovery efforts for the power plant, we had the opportunity to investigate the tsunami traces on Hegura Island. Hegura Island is situated approximately 50 km north of the Noto Peninsula, with dimensions of 1 km from north to south and 2 km from east to west. Its maximum altitude is around 15 m, and the island was formed through volcanic activity between 1000 and 1700 years ago. Port facilities are located at elevations of 1 to 3 m in the southeast area, while the residential area is situated 3 m above sea level. A rocky reef zone extends from west to north in westward.Through field surveys using handheld GPS equipment, we examined the distribution of debris and obtained the map of inundation area. The altitude and distribution of debris were then estimated by plotting the location of debris on a 5mDEM provided by the Geospatial Information Authority of Japan, utilizing GIS technology. Our findings indicated that debris was distributed at higher altitudes in the northern area of the island. Furthermore, it was confirmed that the flooded areas on the southwest and northeast sides were affected by the inflow of the tsunami from outside the port facilities, including the seawall. The maximum altitude of debris distribution on the island was estimated to be approximately 8.3 m, although it may contain errors of several tens of centimeters due to the limited accuracy of the handheld GPS and DEM. In the southwest and northeast sides, the tsunami runup was considered to reach around 6.4 m and 5.0 m, respectively.
During our participation in the recovery efforts for the power plant, we had the opportunity to investigate the tsunami traces on Hegura Island. Hegura Island is situated approximately 50 km north of the Noto Peninsula, with dimensions of 1 km from north to south and 2 km from east to west. Its maximum altitude is around 15 m, and the island was formed through volcanic activity between 1000 and 1700 years ago. Port facilities are located at elevations of 1 to 3 m in the southeast area, while the residential area is situated 3 m above sea level. A rocky reef zone extends from west to north in westward.Through field surveys using handheld GPS equipment, we examined the distribution of debris and obtained the map of inundation area. The altitude and distribution of debris were then estimated by plotting the location of debris on a 5mDEM provided by the Geospatial Information Authority of Japan, utilizing GIS technology. Our findings indicated that debris was distributed at higher altitudes in the northern area of the island. Furthermore, it was confirmed that the flooded areas on the southwest and northeast sides were affected by the inflow of the tsunami from outside the port facilities, including the seawall. The maximum altitude of debris distribution on the island was estimated to be approximately 8.3 m, although it may contain errors of several tens of centimeters due to the limited accuracy of the handheld GPS and DEM. In the southwest and northeast sides, the tsunami runup was considered to reach around 6.4 m and 5.0 m, respectively.