11:00 AM - 1:00 PM
[SSS12-P06] Shallow subsurface structures of the Obitoke fault in the Nara basin based on ultra-rapid-stacking GPR profiling
Keywords:the eastern marginal fault of the Nara basin, Obitoke fault, ground-penetrating radar (GPR), ultra-rapid stacking, shallow subsurface structure, reverse fault
We carried out ground penetrating radar (GPR) profiling across the Obitoke fault in a dissected valley at Imaichi, Nara City. The GPR data were collected by 25 MHz and 50 MHz ultra-rapid-stacking GPR system (pulseEKKO Ultra made by Sensors and Software Inc.). This system can conduct over 32000 to 65000 stacks, in contrast to 64 stacks by conventional system (pulseEKKO PRO). This increases the signal-to-noise ratio and enables to see the more GPR signal at greater depths.
At Imaichi, we carried out trenching and arrayed boring from 2020 to 2021 (MEXT and DPRI, 2021). Prior to these research, we attempted to investigate shallow subsurface structures across the Obitoke fault by GPR surveys, although the obtained profile has a maximum depth of about 2 m. Therefore, we have conducted GPR profiling with depth of 15 m or more by using a high-stacking GPR system to supplement the result of arrayed boring. The obtained profile of the 25 MHz survey shows distinct reflectors from about 6 m to 12 m depth. We inferred that these reflectors display a flexure formed by the Obitoke fault.