5:15 PM - 7:15 PM
[SSS14-P03] Estimation of seismic activity in the northeastern part of the Noto Peninsula based on coastal erosional landforms surveys
Keywords:coastal erosional landforms, emerged sessile assemblages, Noto Peninsula earthquake
In the Noto Peninsula, uplifted landforms such as marine terraces are well developed, and it is thought that earthquakes of M6 or greater with uplift have occurred repeatedly. The seismic uplift is characterized by the presence of coastal erosional landforms, which can be used as an indicator of the old shoreline. Coastal erosional landforms are formed by wave action, mainly on rocky coasts, and include sea cliffs, notches at the base of sea cliffs, caves at the base of sea cliffs, and arches where bedrock is cut into an arch shape. [1] presented a source fault model for historical earthquakes based on the age and the elevation of the emerged sessile assemblages. In the northern Noto Peninsula, rocky coasts are widely distributed, and there are several coastal erosional landforms that have not been reported yet. This study aims to explore and investigate previously undiscovered coastal erosional landforms along the northeastern coast of the Noto Peninsula. Additionally, we will conduct elevation measurements and age determinations of emerged sessile assemblages. By integrating our data with previously reported findings, we seek to improve the resolution of Holocene earthquake records. Furthermore, this research aims to contribute to the assessment of seismic segmentation and the potential for multi-segment rupture events in the Noto region.
This study involved two main components: the exploration of coastal erosional landforms and a detailed investigation of the landforms discovered through the exploration process. The exploration focused on the rocky coastline of northeastern Suzu City, where UAV (drone) surveys and field reconnaissance were conducted to identify coastal erosional features. For the detailed investigation, we employed LiDAR and RTK-GNSS to map the spatial distribution of the identified landforms. Additionally, we conducted elevation measurements, sample collection of uplifted emerged sessile assemblages found within the erosional features, and radiocarbon dating of the collected samples.
In the search for coastal erosional landforms, notches, caves, and arches were found in ten locations. Three of the sites, Dogasaki, Noto-Futami, and Shakuzaki, were investigated in detail. In this presentation, we report on Dogasaki and Noto-Futami.
At Dogasaki, we found a cave. It is about 1.5 m high, 12 m deep, and 4 m wide at maximum, and has an elongated shape with the upper part of the Cave open about 7 m inward from the entrance. We found emerged sessile assemblages (mainly Spirobranchus akitsushima) on walls of east and west. The upper end of the east upper assemblage (NGD02: elevation 2.291 m) and the upper end of the east middle assemblage (NDG01: elevation 1.958 m) were sampled, respectively. The samples obtained were radiocarbon dated by Beta Analytics, Inc. The results showed 1694-1950 cal AD (95.4%) for NDG02 and 1871-1929 cal AD (94.1%) for NDG01.
An arch was found at Noto-Futami. It was about 1.5 m high, 8 m deep, and 3 m wide at maximum, and had not completely detached from the water, with waves intruding into the interior. The south wall of the interior is covered with an emerged sessile assemblage, mainly Chthamalus challengeri and Spirobranchus akitsushima, and samples were taken at 0.955 m, 1.315 m, and 1.745 m elevations, respectively. Radiocarbon dating will be conducted in the future.
Based on the uplift amounts observed at Dogazaki from the May 2023 earthquake (0.21 m) and the 2024 Noto Peninsula Earthquake (1.712 m), NDG01 is considered to have been completely uplifted above sea level during the May 2023 earthquake.
Since NDG02 is situated at a higher elevation than NDG01, it is inferred that an uplift event occurred between AD 1694 and 1929. The most likely candidate for this event is the historical earthquake of 1729[2].
Reference [1] inferred that uplift occurred between the vicinity of Senmaida in Wajima City and Osaki in Suzu City based on the elevation and radiocarbon dating of uplifted biogenic remains. Based on this, a source fault model corresponding to the Wajima Offshore Segment was proposed in [3].
NDG02 is located about 3 km east of the eastern edge of this range and belongs to the Suzu-oki segment, which is distributed to the east of the Wajima-oki segment. This study indicates that the uplift caused by the 1729 historical earthquake was wider than previously reported, and that this earthquake may have been caused by the simultaneous activity of the Wajima-oki segment and a part of the Suzu-oki segment.
References.
[1] Hamada, M., et al. 2016, Tectonophysics, 670, 38-47.
[2] Usami, T., et al, 2013, University of Tokyo Press.
[3] Inoue and Okamura, 2010, Geological Survey of Japan, AIST.
This study involved two main components: the exploration of coastal erosional landforms and a detailed investigation of the landforms discovered through the exploration process. The exploration focused on the rocky coastline of northeastern Suzu City, where UAV (drone) surveys and field reconnaissance were conducted to identify coastal erosional features. For the detailed investigation, we employed LiDAR and RTK-GNSS to map the spatial distribution of the identified landforms. Additionally, we conducted elevation measurements, sample collection of uplifted emerged sessile assemblages found within the erosional features, and radiocarbon dating of the collected samples.
In the search for coastal erosional landforms, notches, caves, and arches were found in ten locations. Three of the sites, Dogasaki, Noto-Futami, and Shakuzaki, were investigated in detail. In this presentation, we report on Dogasaki and Noto-Futami.
At Dogasaki, we found a cave. It is about 1.5 m high, 12 m deep, and 4 m wide at maximum, and has an elongated shape with the upper part of the Cave open about 7 m inward from the entrance. We found emerged sessile assemblages (mainly Spirobranchus akitsushima) on walls of east and west. The upper end of the east upper assemblage (NGD02: elevation 2.291 m) and the upper end of the east middle assemblage (NDG01: elevation 1.958 m) were sampled, respectively. The samples obtained were radiocarbon dated by Beta Analytics, Inc. The results showed 1694-1950 cal AD (95.4%) for NDG02 and 1871-1929 cal AD (94.1%) for NDG01.
An arch was found at Noto-Futami. It was about 1.5 m high, 8 m deep, and 3 m wide at maximum, and had not completely detached from the water, with waves intruding into the interior. The south wall of the interior is covered with an emerged sessile assemblage, mainly Chthamalus challengeri and Spirobranchus akitsushima, and samples were taken at 0.955 m, 1.315 m, and 1.745 m elevations, respectively. Radiocarbon dating will be conducted in the future.
Based on the uplift amounts observed at Dogazaki from the May 2023 earthquake (0.21 m) and the 2024 Noto Peninsula Earthquake (1.712 m), NDG01 is considered to have been completely uplifted above sea level during the May 2023 earthquake.
Since NDG02 is situated at a higher elevation than NDG01, it is inferred that an uplift event occurred between AD 1694 and 1929. The most likely candidate for this event is the historical earthquake of 1729[2].
Reference [1] inferred that uplift occurred between the vicinity of Senmaida in Wajima City and Osaki in Suzu City based on the elevation and radiocarbon dating of uplifted biogenic remains. Based on this, a source fault model corresponding to the Wajima Offshore Segment was proposed in [3].
NDG02 is located about 3 km east of the eastern edge of this range and belongs to the Suzu-oki segment, which is distributed to the east of the Wajima-oki segment. This study indicates that the uplift caused by the 1729 historical earthquake was wider than previously reported, and that this earthquake may have been caused by the simultaneous activity of the Wajima-oki segment and a part of the Suzu-oki segment.
References.
[1] Hamada, M., et al. 2016, Tectonophysics, 670, 38-47.
[2] Usami, T., et al, 2013, University of Tokyo Press.
[3] Inoue and Okamura, 2010, Geological Survey of Japan, AIST.