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[HDS10-P01] Characteristics of the 2024 Noto Peninsula Earthquake Tsunami based on Tsunami Magnitude m
Keywords:The 2024 Noto Peninsula earthquake tsunami, tsunami magnitude m, field surveys, tsunami height, the Japan sea
For the Noto Peninsula earthquake tsunami that occurred on January 1, 2024, we conducted field surveys along the coasts of Yamagata Prefecture to Shimane Prefecture and Sado Island, excluding the area around the source area (Namegaya et al. 2024 JpGU). On the east side of the source area, for example, an inundation height of 2.7 m was measured in Itoigawa City, Niigata Prefecture. To the west of the source area, a runup height of 3.2 m was measured in Hakui, Ishikawa Prefecture. As the distance from the source area increased, it was confirmed that in many areas the tsunami was relatively small, for example, the tsunami did not exceed the quay wall. However, in some areas, a tsunami height of 1.4 m was measured along the coast of Hyogo Prefecture, which was larger than that of the surrounding areas.
We estimated the tsunami magnitude m (Hatori 1986) of the 2024 Noto Peninsula earthquake tsunami using our survey results, the field survey results by Yuhi et al. (2024), those by Takashimizu et al. (2024), and tide gauge records. The tsunami magnitude m is based on the idea that wave heights decay in proportion to the minus first power of the shortest distance at sea from the epicenter, and the quantity is evaluated in increments of 0.5, which is useful for understanding the overall tsunami scale. As a result, the tsunami magnitude m of the 2024 Noto Peninsula earthquake tsunami is estimated to be 1.5, although there is some large variation (Namegaya et al. 2024 SSJ).
Next, the ratio (H/Hest) of the measured actual tsunami height (H) to the tsunami height (Hest) estimated from the tsunami magnitude m and the information on the shortest distance at sea from the epicenter was taken. The ratio was found to exceed 5 in Joetsu City in southern Niigata Prefecture. In fact, the tsunami heights in this area exceeded 6 m in some places (Yuhi et al. 2024), which is considerably higher than the surrounding areas. The reason of this is unknown, but may be due to topography, the presence of secondary wave sources, or, as pointed out by Heidarzadeh et al. (2024), due to directivity from the wave source.
We also examined the relationship between earthquake magnitude M and tsunami magnitude m for earthquakes that have occurred with tsunamis in the Japan Sea to date, including historical earthquakes. We found that the tsunami magnitude m of the 2024 Noto Peninsula earthquake tsunami was slightly smaller than the tsunami magnitude m of other earthquakes of similar earthquake magnitude M. The results for other earthquakes and tsunamis show that the tsunami magnitude m tends to be smaller for earthquakes whose source areas are located partly on the land of Honshu than for earthquakes whose source areas are located in the sea. This tendency is thought to be due to the fact that only a part of the energy of the uplift is transmitted to the seawater.
We estimated the tsunami magnitude m (Hatori 1986) of the 2024 Noto Peninsula earthquake tsunami using our survey results, the field survey results by Yuhi et al. (2024), those by Takashimizu et al. (2024), and tide gauge records. The tsunami magnitude m is based on the idea that wave heights decay in proportion to the minus first power of the shortest distance at sea from the epicenter, and the quantity is evaluated in increments of 0.5, which is useful for understanding the overall tsunami scale. As a result, the tsunami magnitude m of the 2024 Noto Peninsula earthquake tsunami is estimated to be 1.5, although there is some large variation (Namegaya et al. 2024 SSJ).
Next, the ratio (H/Hest) of the measured actual tsunami height (H) to the tsunami height (Hest) estimated from the tsunami magnitude m and the information on the shortest distance at sea from the epicenter was taken. The ratio was found to exceed 5 in Joetsu City in southern Niigata Prefecture. In fact, the tsunami heights in this area exceeded 6 m in some places (Yuhi et al. 2024), which is considerably higher than the surrounding areas. The reason of this is unknown, but may be due to topography, the presence of secondary wave sources, or, as pointed out by Heidarzadeh et al. (2024), due to directivity from the wave source.
We also examined the relationship between earthquake magnitude M and tsunami magnitude m for earthquakes that have occurred with tsunamis in the Japan Sea to date, including historical earthquakes. We found that the tsunami magnitude m of the 2024 Noto Peninsula earthquake tsunami was slightly smaller than the tsunami magnitude m of other earthquakes of similar earthquake magnitude M. The results for other earthquakes and tsunamis show that the tsunami magnitude m tends to be smaller for earthquakes whose source areas are located partly on the land of Honshu than for earthquakes whose source areas are located in the sea. This tendency is thought to be due to the fact that only a part of the energy of the uplift is transmitted to the seawater.