1:45 PM - 2:00 PM
[SSS14-13] Excavation survey of lower terraces in the northern coast of the Noto Peninsula
★Invited Papers
Keywords:Noto Peninsula Earthquake, Uplift, Marine terrace, Excavation survey
During the 2024 Noto Peninsula earthquake (M7.6), the coast was greatly uplifted and marine terraces were formed (Shishikura et al., 2024). Holocene marine terraces divided into three levels (L1 to L3 in descending order) are distributed along the northern coast of the Noto Peninsula, and it is suggested that large uplift earthquakes as well as the 2024 event have occurred repeatedly (Shishikura et al., 2020). However, no clear data on the timing of past earthquakes (formation age of terraces) has been provided. In this study, we conducted an excavation survey on the terrace surface, observed the terrace composition and covering layers, and collected dating samples to clarify the age of the marine terraces.
Excavation surveys were conducted at five locations in Orito, Takaya, Kataiwa in Suzu City, and Sosogi and Nafune in Wajima City along the coast facing the submarine active fault identified by Inoue and Okamura (2010). The former three sites face the Suzu-oki segment, and the latter two sites face the Wajima-oki segment. Excavation was conducted using a combination of pit excavation with small backhoe or shovel (up to 1–2 m in depth), hammer coring, and hand auger (up to 3 m in depth). At many sites, marine sand layers containing with shell fragments or marine gravels consisting of rounded to sub-rounded pebbles and cobbles were observed comprising the terraces. Commonly observed at several sites were silt layers showing chaotic facies mixed with angular gravels which are presumed to be derived from the landslide and the resulting debris flow, and that overlay the terrace components.
This stratigraphy can be observed in the present coast. In September 2024, landslide have occurred in many places due to the heavy rainfall that hit the Noto area, and debris flow deposit covered the beach sand, gravel and wave-cut-bench which emerged due to the uplift of the 2024 earthquake. This modern analogue indicates that the same series of events that occurred in 2024 may have occurred in the past. Dating samples were also collected from each stratigraphic level, and the results will be presented in this meeting.
Excavation surveys were conducted at five locations in Orito, Takaya, Kataiwa in Suzu City, and Sosogi and Nafune in Wajima City along the coast facing the submarine active fault identified by Inoue and Okamura (2010). The former three sites face the Suzu-oki segment, and the latter two sites face the Wajima-oki segment. Excavation was conducted using a combination of pit excavation with small backhoe or shovel (up to 1–2 m in depth), hammer coring, and hand auger (up to 3 m in depth). At many sites, marine sand layers containing with shell fragments or marine gravels consisting of rounded to sub-rounded pebbles and cobbles were observed comprising the terraces. Commonly observed at several sites were silt layers showing chaotic facies mixed with angular gravels which are presumed to be derived from the landslide and the resulting debris flow, and that overlay the terrace components.
This stratigraphy can be observed in the present coast. In September 2024, landslide have occurred in many places due to the heavy rainfall that hit the Noto area, and debris flow deposit covered the beach sand, gravel and wave-cut-bench which emerged due to the uplift of the 2024 earthquake. This modern analogue indicates that the same series of events that occurred in 2024 may have occurred in the past. Dating samples were also collected from each stratigraphic level, and the results will be presented in this meeting.