5:15 PM - 6:45 PM
[SSS11-P04] Estimated displacement of paleoearthquake events using detailed topographical measurements on the Kamishiro fault in the northern part of the IST
Keywords:Kamishiro Fault, landform evolution, paleo earthquake, Itoigawa-Shizuoka Tectonic active fault zone, laser scanning
The 2014 Northern Nagano Prefecture Earthquake (Kamishiro Fault Earthquake) (Mj6.7), which occurred at around 22:08 JST on November 22, 2014, created a clear surface rupture approximately 9 km long along the Kamishiro fault in the northern part of the Itoigawa-Shizuoka tectonic line (Hirouchi et al., 2014 etc.). Previous earthquake assessments of the Kamishiro Fault estimated that an earthquake of around M7.5 would occur (Suzuki et al., 2010). Furthermore, the expected vertical displacement was thought to be 1.5m to 3.0m (Matta et al., 2006). However, the scale of the earthquake that occurred in 2014 was much smaller than previously estimated, and the maximum vertical displacement due to the earthquake was approximately 0.8 m (Ishimura et al., 2015, etc.). Therefore, the 2014 earthquake is considered to be inconsistent with the topographically and geologically estimated characteristic earthquake of the Kamishiro Fault (Katsube et al., 2017). Evaluation of smaller earthquakes with such large displacements is a challenge for long-term earthquake evaluation. Therefore, it is necessary to clarify the relationship between unique earthquakes and earthquakes like the one in 2014 by acquiring further paleo-earthquake data and reexamining the earthquake's scale and sense of motion.
In general, it is difficult to accurately measure the amount of horizontal displacement by taking into consideration the shape of the terrace cliff, etc., which serves as a reference, compared to vertical displacement. However, in recent years, with advances in topographic measurement technology such as laser surveying, attempts have been made to measure strike-slip displacement by conducting topographic surveying using DTM and other methods (Nakata et al., 2008).
In this study, we created detailed topographical data at 5cm intervals from laser surveying of the river terraces displaced by the activity of the Kamishiro Fault, and examined the diversity of the sense of movement of the Kamishiro Fault by deriving the vertical slip displacement and strike slip displacement for each paleoearthquake,.
There are two survey areas: Area 1 on the right bank of the Hime River in Warabidaira, Hakuba Village, which corresponds to the M side of Sugito et al. (2015), and Area 2, which is part of a rice field on the old river channel of the Matsukawa River in Morikami. LIVOX's Avia was used to acquire the topographic data, and point cloud topographic data was acquired over three days: April 30, 2023, and December 7-8, 2023.
The total number of point cloud data acquired on the right bank of the Hime River in Warabidaira, Hakuba Village in Area 1 was 228,281,205 points before removing noise such as plants. The acquired point cloud data was processed into DTM after removing points other than the ground surface such as plants using the analysis software TRENDPOINT to create a 5cm mesh. In addition, by clarifying the slope direction using QGIS, the direction of erosion of the paleo stream was shown, and this was used as a reference for determining that the river terraces were the same surface. Then, for each river terrace surface, those with similar characteristics of terrace scarp orientation and erosion direction were determined to be the same river terrace surface, and the amount of strike slip was analyzed. Furthermore, a cross-sectional view was created using Global Mapper, and the amount of vertical displacement was also measured. Furthermore, when we defined the terrace surfaces as L1 to L8 in order from the oldest terrace surface, the results showed that there was almost no difference in vertical displacement from that reported by Matta et al. (2006), but different results were obtained regarding the amount of lateral slip.
In Area 2, near the left bank of the Matuskawa River in Moriue, several terraces were identified based on geomorphic stereo analysis of aerial photographs taken by the US military up to 1948. As a result, some areas were confirmed where the downstream side is more uplifted than the upstream side (Matta et al., 2006). This time, our measurement by a handy laser surveyor to obtain topographical data around the area. The total number of acquired point clouds was 91,057,126 points, from which a 10cm mesh and cross-sectional view were created using Global Mapper. Although it was not possible to determine the exact amount of uplift due to many artificial alterations, it was possible to confirm from the cross-sectional diagram that the upstream side of the old river channel was higher than the downstream side.
In general, it is difficult to accurately measure the amount of horizontal displacement by taking into consideration the shape of the terrace cliff, etc., which serves as a reference, compared to vertical displacement. However, in recent years, with advances in topographic measurement technology such as laser surveying, attempts have been made to measure strike-slip displacement by conducting topographic surveying using DTM and other methods (Nakata et al., 2008).
In this study, we created detailed topographical data at 5cm intervals from laser surveying of the river terraces displaced by the activity of the Kamishiro Fault, and examined the diversity of the sense of movement of the Kamishiro Fault by deriving the vertical slip displacement and strike slip displacement for each paleoearthquake,.
There are two survey areas: Area 1 on the right bank of the Hime River in Warabidaira, Hakuba Village, which corresponds to the M side of Sugito et al. (2015), and Area 2, which is part of a rice field on the old river channel of the Matsukawa River in Morikami. LIVOX's Avia was used to acquire the topographic data, and point cloud topographic data was acquired over three days: April 30, 2023, and December 7-8, 2023.
The total number of point cloud data acquired on the right bank of the Hime River in Warabidaira, Hakuba Village in Area 1 was 228,281,205 points before removing noise such as plants. The acquired point cloud data was processed into DTM after removing points other than the ground surface such as plants using the analysis software TRENDPOINT to create a 5cm mesh. In addition, by clarifying the slope direction using QGIS, the direction of erosion of the paleo stream was shown, and this was used as a reference for determining that the river terraces were the same surface. Then, for each river terrace surface, those with similar characteristics of terrace scarp orientation and erosion direction were determined to be the same river terrace surface, and the amount of strike slip was analyzed. Furthermore, a cross-sectional view was created using Global Mapper, and the amount of vertical displacement was also measured. Furthermore, when we defined the terrace surfaces as L1 to L8 in order from the oldest terrace surface, the results showed that there was almost no difference in vertical displacement from that reported by Matta et al. (2006), but different results were obtained regarding the amount of lateral slip.
In Area 2, near the left bank of the Matuskawa River in Moriue, several terraces were identified based on geomorphic stereo analysis of aerial photographs taken by the US military up to 1948. As a result, some areas were confirmed where the downstream side is more uplifted than the upstream side (Matta et al., 2006). This time, our measurement by a handy laser surveyor to obtain topographical data around the area. The total number of acquired point clouds was 91,057,126 points, from which a 10cm mesh and cross-sectional view were created using Global Mapper. Although it was not possible to determine the exact amount of uplift due to many artificial alterations, it was possible to confirm from the cross-sectional diagram that the upstream side of the old river channel was higher than the downstream side.