5:15 PM - 6:45 PM
[U15-P83] Survey of coastal uplift associated with the 2023 and 2024 Noto Peninsula earthquakes based on the height distribution of emerged sessile assemblage
Keywords:Noto Peninsula Earthquake, coastal uplift, emerged sessile assemblage
In order to clarify crustal and topographic movement associated with the M6.5 earthquake that occurred in the northeastern part of the Noto Peninsula on May 5, 2023 (The Headquaters for Earthquake Research Promotion, 2023), as well as the M7.6 earthquake that occurred on January 1, 2024 (The Headquaters for Earthquake Research Promotion, 2024), a survey of coastal uplift based on the height of distribution of emerged sessile assemblage was conducted.
1. Survey of Coastal Uplift due to the May 5, 2023 Earthquake
According to the Synthetic Aperture Radar (SAR) interferometry analysis by the Geospatial Information Authority of Japan (2023), the uplift caused by the earthquake on May 5, 2023, was estimated to be approximately 20 cm at a maximum within a radius of 8 km centered around Shakuzaki in the northern part of Orito-machi, Suzu City. A field survey conducted on May 6, 2023, immediately after the earthquake, revealed the exposure of emerged sessile assemblage inhabiting the intertidal zone, such as Saccostrea kegaki Torigoe & Inaba and Crassostrea gigas on rocky reefs and quay along the coast, as well as Spirobranchus akitsushima, considered as an indicator of shoreline. It was presumed that these sessile perished due to the uplift during the earthquake. The height of distribution of these sessile above the sea surface was measured at various locations in the northern part of Suzu City, and the uplift was calculated by subtracting the difference between the tidal level observations at the time of measurement and the average tidal level over five years from these measured values. As a result, the uplift was found to be up to approximately 0.3 m, with the peak occurring in the area approximately 1 km east-west from Shakuzaki to the Noroshi Fishing Port. These uplift is consistent with SAR interferometry analysis and Shishikura et al. (2023), suggesting that it may reflect the distribution of displacement caused by the offshore active fault.
2. Survey of coastal uplift associated with the 2024 Noto Peninsula Earthquake (M7.6)
During the field survey conducted after the 2024 Noto Peninsula Earthquake (M7.6), it was observed that sandy and rocky coast expanded significantly throughout the uplifted areas. It was also noted that the upper boundary of Corallina pilulifera, which inhabits below the intertidal zone exposed above the sea surface, continuously extended horizontally. The upper boundary of Corallina pilulifera coincided with the lower distribution limit of Spirobranchus akitsushima in many locations. Furthermore, in rocky reef areas, an assemblage of Spirobranchus akitsushima remains was observed above a notch, while Corallina pilulifera remains clustered below. Based on these observations, it was inferred that the upper boundary of Corallina pilulifera indicates the pre-uplift mean sea level. At a total of 98 locations across the northern Noto Peninsula, the height of distribution from the sea surface of Corallina pilulifera's upper boundary were measured using laser surveys. As tidal observation records are missing in the northern Noto Peninsula, the difference between astronomical tide and the average tide over five years was subtracted from the measured values to determine the uplift. Consequently, the maximum uplift amounts in the northern Suzu City and the western Wajima City were approximately 2.6 meters (around Nagahashi-machi in Suzu City) and approximately 4.7 meters (around Fukami in Wajima City), respectively. Coastal uplift extends widely across the northern Noto Peninsula and is generally consistent with the uplift distribution obtained from SAR interferometric analysis by the Geospatial Information Authority of Japan (2024). Additionally, the uplift distribution generally corresponds with the height of distribution of ancient sealevels reported by Shishikura et al. (2020), suggesting that the lower terraces in the northern Noto Peninsula may have been formed by repeated M7~ class earthquakes along offshore active faults. Identifying the ages of these lower terraces may enable estimation of the activity of the active faults off the coast of the Noto Peninsula. The authors are continuing additional surveys, and more precise results will be reported at the time of publication.
This work was supported by JSPS KAKENHI Grant Number 23K17482.
1. Survey of Coastal Uplift due to the May 5, 2023 Earthquake
According to the Synthetic Aperture Radar (SAR) interferometry analysis by the Geospatial Information Authority of Japan (2023), the uplift caused by the earthquake on May 5, 2023, was estimated to be approximately 20 cm at a maximum within a radius of 8 km centered around Shakuzaki in the northern part of Orito-machi, Suzu City. A field survey conducted on May 6, 2023, immediately after the earthquake, revealed the exposure of emerged sessile assemblage inhabiting the intertidal zone, such as Saccostrea kegaki Torigoe & Inaba and Crassostrea gigas on rocky reefs and quay along the coast, as well as Spirobranchus akitsushima, considered as an indicator of shoreline. It was presumed that these sessile perished due to the uplift during the earthquake. The height of distribution of these sessile above the sea surface was measured at various locations in the northern part of Suzu City, and the uplift was calculated by subtracting the difference between the tidal level observations at the time of measurement and the average tidal level over five years from these measured values. As a result, the uplift was found to be up to approximately 0.3 m, with the peak occurring in the area approximately 1 km east-west from Shakuzaki to the Noroshi Fishing Port. These uplift is consistent with SAR interferometry analysis and Shishikura et al. (2023), suggesting that it may reflect the distribution of displacement caused by the offshore active fault.
2. Survey of coastal uplift associated with the 2024 Noto Peninsula Earthquake (M7.6)
During the field survey conducted after the 2024 Noto Peninsula Earthquake (M7.6), it was observed that sandy and rocky coast expanded significantly throughout the uplifted areas. It was also noted that the upper boundary of Corallina pilulifera, which inhabits below the intertidal zone exposed above the sea surface, continuously extended horizontally. The upper boundary of Corallina pilulifera coincided with the lower distribution limit of Spirobranchus akitsushima in many locations. Furthermore, in rocky reef areas, an assemblage of Spirobranchus akitsushima remains was observed above a notch, while Corallina pilulifera remains clustered below. Based on these observations, it was inferred that the upper boundary of Corallina pilulifera indicates the pre-uplift mean sea level. At a total of 98 locations across the northern Noto Peninsula, the height of distribution from the sea surface of Corallina pilulifera's upper boundary were measured using laser surveys. As tidal observation records are missing in the northern Noto Peninsula, the difference between astronomical tide and the average tide over five years was subtracted from the measured values to determine the uplift. Consequently, the maximum uplift amounts in the northern Suzu City and the western Wajima City were approximately 2.6 meters (around Nagahashi-machi in Suzu City) and approximately 4.7 meters (around Fukami in Wajima City), respectively. Coastal uplift extends widely across the northern Noto Peninsula and is generally consistent with the uplift distribution obtained from SAR interferometric analysis by the Geospatial Information Authority of Japan (2024). Additionally, the uplift distribution generally corresponds with the height of distribution of ancient sealevels reported by Shishikura et al. (2020), suggesting that the lower terraces in the northern Noto Peninsula may have been formed by repeated M7~ class earthquakes along offshore active faults. Identifying the ages of these lower terraces may enable estimation of the activity of the active faults off the coast of the Noto Peninsula. The authors are continuing additional surveys, and more precise results will be reported at the time of publication.
This work was supported by JSPS KAKENHI Grant Number 23K17482.