5:15 PM - 7:15 PM
[SSS14-P01] Geologic structure along the Wakayama River, Noto Peninsula mainly about the Okata Anticline
Keywords:2024 Noto Peninsula earthquake, Wakayama River, earthquake-induced faults, anticline, nontectonic structure, landslide
Fault scarplets popped out by the 2024 Noto Peninsula Earthquake along the Wakayama River flowing in Suzu City, Ishikawa Prefecture. Various tectonic or nontectonic causes are assumed to be the genesis of the faults, so topography and geologic structure in this area should be considered. I present the result of an investigation of the geologic structure mainly about the Okata Anticline described in the 1/50,000 geological quadrangle map. The map shows the two synclines (Kumandani and Wakayamagawa) and the Okata Anticline between the synclines along Wakayama River course.
Kamikuromaru- Munesue, Wakayama-cho: The Okata Anticline is inferred to be located along the river floor. Around Munesue, the anticline axis is certainly traced in a northeast direction. The right-stepping echelon arrangement of the axis can be estimated. An asymmetrical fold of which the south wing dips steeply and an open fold with an unclear axial plane are observed. Common characteristics along the earthquake-induced faults are that the limb at least one side dips steeply and many fracture zones are accompanied.
Naka- Daibo, Wakayama-cho: The location of the axial plane is uncertain because of poor exposures along the river in this area. Whereas, bedding planes tend to be inclined southward on the south-facing left bank and inclined northward on the north-facing right bank. Strata incline steeply along the fault induced by the earthquake.
Nobutake, Wakayama-cho: The earthquake-induced faults and flexure imply the growth of the anticline, but the poor exposures do not make clear the anticlinal structure. Also in this area, strata incline valleyward on both river banks.
The above-mentioned results of the investigation indicate that the Okata Anticline does not continue as the illustration of the geological quadrangle map, but is a group of short culminations arranged en echelon. Furthermore, a part of the anticline may not exist. The anticline is accompanied by brittle fracture zones, which means the formation in shallow depth. Such arrangement and characteristics of the structure suggest that nontectonic factors like the rebound of the valley bottom associated with the denudation by the Wakayama River and landslides movement on both sides of the valley dip slope are affected by the formation of the Okata Anticline. The earthquake fault scarplets may have been formed under similar factors.
Kamikuromaru- Munesue, Wakayama-cho: The Okata Anticline is inferred to be located along the river floor. Around Munesue, the anticline axis is certainly traced in a northeast direction. The right-stepping echelon arrangement of the axis can be estimated. An asymmetrical fold of which the south wing dips steeply and an open fold with an unclear axial plane are observed. Common characteristics along the earthquake-induced faults are that the limb at least one side dips steeply and many fracture zones are accompanied.
Naka- Daibo, Wakayama-cho: The location of the axial plane is uncertain because of poor exposures along the river in this area. Whereas, bedding planes tend to be inclined southward on the south-facing left bank and inclined northward on the north-facing right bank. Strata incline steeply along the fault induced by the earthquake.
Nobutake, Wakayama-cho: The earthquake-induced faults and flexure imply the growth of the anticline, but the poor exposures do not make clear the anticlinal structure. Also in this area, strata incline valleyward on both river banks.
The above-mentioned results of the investigation indicate that the Okata Anticline does not continue as the illustration of the geological quadrangle map, but is a group of short culminations arranged en echelon. Furthermore, a part of the anticline may not exist. The anticline is accompanied by brittle fracture zones, which means the formation in shallow depth. Such arrangement and characteristics of the structure suggest that nontectonic factors like the rebound of the valley bottom associated with the denudation by the Wakayama River and landslides movement on both sides of the valley dip slope are affected by the formation of the Okata Anticline. The earthquake fault scarplets may have been formed under similar factors.