10:15 AM - 10:30 AM
[SSS10-06] The Quaternary fault outcrop of the Inagoe fault, Furukawa fault zone, in northern part of Gifu Prefecture, central Japan
Keywords:Inagoe fault, Quaternary fault outcrop, Tectonic landforms, 1858AD Hietsu earthquake
Inagoe fault, trending NE–SW ~ ENE–WSW and extending 13 km in length, is one of the Quaternary faults of the Furukawa fault zone located in Gifu Prefecture, Hida city (Suzuki and Sugito, 2010; Kumabara, 2019; Kumabara et al., 2019). Although the Quaternary fault outcrop was confirmed in the eastern part of the Inagoe fault (Research Group for the Active Faults of Gifu Prefecture, 2008), there are no reports on the direct evidences such as the Quaternary fault outcrop in the western extension of the Inagoe fault toward Kurigatani-gawa area by topographical studies (Suzuki and Sugito, 2010; Kumabara, 2019; Kumabara et al., 2019). This study reports the detail characteristics of the newly-found Quatrenary fault outcrop, and discuss the latest event in the western part of the Inagoe fault.
The 5-m-wide fault zone is composed of fault gouge and fault breccia, which is located on the fault trace detected by the topographical studies (Suzuki and Sugito, 2010; Kumabara, 2019; Kumabara et al., 2019). The approximate strike and dip of this fault zone are N55° E85° S, and composite planar fabrics containing P-foliation and R1 shear shows dextral sense of shear in its fault gouge zone. While unconsolidated sand-gravel layers unconformably underlain by the fault zone, the partial layers were sandwiched within the fault zone. Major axis of the gravels adjacent to the fault gouge were oriented vertically, and striations on its surface were recognized. A humic soil was partially included in the sand-gravel layer; radiocarbon age of the humic soil sample showed AD 1527–1658 cal. BP.
This fault outcrop is located on the fault trace of the Inagoe fault as mentioned above, which strike coincides with direction of the fault trace. In addition, dextral sense of shear recognized by composite planar fabrics in the gouge zone was confirmed, which is consistent with the right-lateral tectonic landforms. These evidences indicate that this fault outcrop is thought to be the fault core of the Inagoe fault. Furthermore, sandwiched sand-gravel layers within the fault zone, vertical orientation of the gravels and striation on the surface of gravels suggest that the sand-gravel layers fell into tensile crack and deformed by the movement of the fault. This event is considered to be after AD 1527–1658 cal. BP because of the radiocarbon age. Historical earthquakes which occurred in northern Gifu prefecture include the AD 1586 Tensho earthquake, AD 1826 earthquake at Hida Ono-gun (M6.0), and AD 1855 Hida-Shirakawa and Kanazawa earthquake (M6.8) and AD 1858 Hietsu earthquake (Usami, 1987). Hence, we concluded that the latest event of the Inagoe fault may correspond to either of the historical earthquakes.
The 5-m-wide fault zone is composed of fault gouge and fault breccia, which is located on the fault trace detected by the topographical studies (Suzuki and Sugito, 2010; Kumabara, 2019; Kumabara et al., 2019). The approximate strike and dip of this fault zone are N55° E85° S, and composite planar fabrics containing P-foliation and R1 shear shows dextral sense of shear in its fault gouge zone. While unconsolidated sand-gravel layers unconformably underlain by the fault zone, the partial layers were sandwiched within the fault zone. Major axis of the gravels adjacent to the fault gouge were oriented vertically, and striations on its surface were recognized. A humic soil was partially included in the sand-gravel layer; radiocarbon age of the humic soil sample showed AD 1527–1658 cal. BP.
This fault outcrop is located on the fault trace of the Inagoe fault as mentioned above, which strike coincides with direction of the fault trace. In addition, dextral sense of shear recognized by composite planar fabrics in the gouge zone was confirmed, which is consistent with the right-lateral tectonic landforms. These evidences indicate that this fault outcrop is thought to be the fault core of the Inagoe fault. Furthermore, sandwiched sand-gravel layers within the fault zone, vertical orientation of the gravels and striation on the surface of gravels suggest that the sand-gravel layers fell into tensile crack and deformed by the movement of the fault. This event is considered to be after AD 1527–1658 cal. BP because of the radiocarbon age. Historical earthquakes which occurred in northern Gifu prefecture include the AD 1586 Tensho earthquake, AD 1826 earthquake at Hida Ono-gun (M6.0), and AD 1855 Hida-Shirakawa and Kanazawa earthquake (M6.8) and AD 1858 Hietsu earthquake (Usami, 1987). Hence, we concluded that the latest event of the Inagoe fault may correspond to either of the historical earthquakes.