11:45 AM - 12:00 PM
[HDS09-10] Activities of the Togigawa-Nangan Fault associated with the 2020 Noto Earthquake
★Invited Papers
Keywords:2024 Noto Earthquake, active fault, earthquake fault, Togigawa-Nangan Fault
The Togigawa-Nangan Fault (Research Groupe for Active Faults of Japan, 1981) is an active fault with a northeast-southwest strike that was identified by Ota et al. (1976) based on the discontinuity in the altitude distribution of marine terraces during the last interglacial period. Watanabe et al. (2015) reconfirmed the activity of this fault based on the altitude distribution of newer or even older marine terraces. Its location is thought to be near the southern edge of the lowland along the Togi River, but it was not clearly shown in Nakata and Imaizumi (2002) because of the lack of clear fault displacement topography.
During the 2024 Noto Earthquake, ground deformation of less than a few tens of centimeters occurred along the northeast-southwest line where this fault is inferred to exist. There, the southeast side of the line was gently uplifted by several tens of centimeters, accompanied by left-lateral strike slip of about 10 to several tens of centimeters. Definite deformation was confirmed at least 5 locations along the 3km long line. These include deformation of the road surface, continuous fractures on rice fields, and deformation of block walls.
The fault passed near the mouth of the Togi River and raised the area around Ryoke fishing port on the left bank of the Togi River by about 30 cm. The fault may extend further into the southwest ocean. Damage to buildings in areas along the fault trace is significant.
A discontinuity in the pattern of SAR interference fringes was found over a wide area in the northern part of the Noto Peninsula, and the location where the Togikawa south bank fault appeared is part of this discontinuity. Ground deformation on the surface is also confirmed by the vertical differences in LiDAR data before and after the earthquake.
Significance:
The left-lateral strike slip observed here is consistent with the fact that the westward horizontal movement of GNSS is large (86.9 cm) in Togi, north of this fault, and small (8.6 cm) in Shiga, south of this fault. However, it is inconsistent with the normal wide-area east-west compressive stress field. It is thought that the north-south compression caused by the activity of the submarine thrust fault along the north coast of the Noto Peninsula, which caused the M7.6 earthquake, may have been the trigger. The displacement of the Togigawa Nangan Fault may be incidental to the main shock, but it is not thought to be simply induced by shaking.
Furthermore, this fault is located 9km north of the Shika nuclear power plant, and its existence has been denied for many years during safety reviews. However, a report submitted to the Nuclear Safety Commission in October 2023 identified a 9km-long active fault based on the existence of a discontinuous gravitational anomaly.
During the 2024 Noto Earthquake, ground deformation of less than a few tens of centimeters occurred along the northeast-southwest line where this fault is inferred to exist. There, the southeast side of the line was gently uplifted by several tens of centimeters, accompanied by left-lateral strike slip of about 10 to several tens of centimeters. Definite deformation was confirmed at least 5 locations along the 3km long line. These include deformation of the road surface, continuous fractures on rice fields, and deformation of block walls.
The fault passed near the mouth of the Togi River and raised the area around Ryoke fishing port on the left bank of the Togi River by about 30 cm. The fault may extend further into the southwest ocean. Damage to buildings in areas along the fault trace is significant.
A discontinuity in the pattern of SAR interference fringes was found over a wide area in the northern part of the Noto Peninsula, and the location where the Togikawa south bank fault appeared is part of this discontinuity. Ground deformation on the surface is also confirmed by the vertical differences in LiDAR data before and after the earthquake.
Significance:
The left-lateral strike slip observed here is consistent with the fact that the westward horizontal movement of GNSS is large (86.9 cm) in Togi, north of this fault, and small (8.6 cm) in Shiga, south of this fault. However, it is inconsistent with the normal wide-area east-west compressive stress field. It is thought that the north-south compression caused by the activity of the submarine thrust fault along the north coast of the Noto Peninsula, which caused the M7.6 earthquake, may have been the trigger. The displacement of the Togigawa Nangan Fault may be incidental to the main shock, but it is not thought to be simply induced by shaking.
Furthermore, this fault is located 9km north of the Shika nuclear power plant, and its existence has been denied for many years during safety reviews. However, a report submitted to the Nuclear Safety Commission in October 2023 identified a 9km-long active fault based on the existence of a discontinuous gravitational anomaly.