5:15 PM - 6:45 PM
[SSS11-P02] Detection of displacement microtopography of the Sarukawa Fault by UAV laser surveying and estimation of shallow subsurface structure by boring
Keywords:UAV laser surveying, Sarukawa fault, Oga Peninsula
Sarukawa Fault in the northern coast of the Oga Peninsula in Akita Prefecture is an N-S-striking and east-dipping reverse fault, separating the Iriai Lowland from the Katanishi Terrace. Although the length of the fault on land is about 5 km, a fault plane has been found at a coastal outcrop (Active Fault research Group 1991, Active Fault in Japan), and the fault is thought to extend long into the northern sea area. The Katanishi Terrace is displaced by the NE-SW-trending anticline and the terrace surface is lowered westward by a clear deflection near the fault and submerged under the Iriai Lowland.
In this study, we conducted boring surveys at three locations near the Sarukawa Fault trace and analyzed the topography of the flexure scarp using UAV laser surveying to investigate the relationship between the subsurface structure around the fault and surface displacement.
Alluvial deposits in the Iriai Lowland, about 30 m west of the base of the flexure scarp, consist of a soft sandy layer overlain by a peat layer about 2 m thick at the surface, reaching the relatively well-compacted Katanishi Formation sand layer at 12 m depth. The Katanishi Formation sandy layer, with a small amount of fine gravels, occupies the entire depth of the excavation at the flexure scarp on the east side of the fault, and modelate faults are developed at a frequency of 0~2 faults/m below 20 m. The boring was also carried out on the east side of the fault trace. Although the excavation did not reach the fault plane, the fault plane is estimated to be deeper than 10 m and 26 m at a horizontal distance of 3 m and 25 m east of the fault trace, respectively, and a slightly high-angle fault plane is inferred at shallow depths.
We conducted a UAV (drone) laser survey along the eastern margin of the Iriai Lowland in a section 500 m north-south and 1,000 m east-west across the flexure topography. Laser surveying was conducted using a DJI Matrice 300 RTK drone equipped with a Zenmuse L1, with measurements taken directly below (90°) and at an angle of 60° at 0.5 m intervals. Because the surveyed area has an altitude difference of about 40 m, measurements were taken at an altitude of about 80 m. Ground data was extracted from the measured data by removing buildings, trees, and other ground objects, and detailed plan and cross-sectional views of the topography were created.
Several small steps parallel to or subparallel to the main fault trace were detected on the eastern-side of fault. On the upper part of the flexure cliff, there is a rise, and on the east side of the rise, a trough topography with a width of about 100 m, which is 2 to 3 m lower than the surrounding area, is developed. This structure may be the result of displacement by backthrusting and normal faulting associated with and flexural deformation.
In this study, we conducted boring surveys at three locations near the Sarukawa Fault trace and analyzed the topography of the flexure scarp using UAV laser surveying to investigate the relationship between the subsurface structure around the fault and surface displacement.
Alluvial deposits in the Iriai Lowland, about 30 m west of the base of the flexure scarp, consist of a soft sandy layer overlain by a peat layer about 2 m thick at the surface, reaching the relatively well-compacted Katanishi Formation sand layer at 12 m depth. The Katanishi Formation sandy layer, with a small amount of fine gravels, occupies the entire depth of the excavation at the flexure scarp on the east side of the fault, and modelate faults are developed at a frequency of 0~2 faults/m below 20 m. The boring was also carried out on the east side of the fault trace. Although the excavation did not reach the fault plane, the fault plane is estimated to be deeper than 10 m and 26 m at a horizontal distance of 3 m and 25 m east of the fault trace, respectively, and a slightly high-angle fault plane is inferred at shallow depths.
We conducted a UAV (drone) laser survey along the eastern margin of the Iriai Lowland in a section 500 m north-south and 1,000 m east-west across the flexure topography. Laser surveying was conducted using a DJI Matrice 300 RTK drone equipped with a Zenmuse L1, with measurements taken directly below (90°) and at an angle of 60° at 0.5 m intervals. Because the surveyed area has an altitude difference of about 40 m, measurements were taken at an altitude of about 80 m. Ground data was extracted from the measured data by removing buildings, trees, and other ground objects, and detailed plan and cross-sectional views of the topography were created.
Several small steps parallel to or subparallel to the main fault trace were detected on the eastern-side of fault. On the upper part of the flexure cliff, there is a rise, and on the east side of the rise, a trough topography with a width of about 100 m, which is 2 to 3 m lower than the surrounding area, is developed. This structure may be the result of displacement by backthrusting and normal faulting associated with and flexural deformation.