9:00 AM - 9:15 AM
[SSS11-01] Electric resistivity tomography (ERT) at the Sarukawa fault in Oga peninsula, northeast of Japan
Keywords:Electric Sounding, ERT (Electric Resistivity Tomography), Sarukawa fault, Thrust fault
Sarukawa fault is one of active faults but the recent earthquake dislocated the Sarukawa fault is unknown, even though some candidates of the damaged earthquakes are proposed. The lineament in the topography can be seen due to fault activity but its buried angle of the fault dislocation to the ground surface is not clearly observed so far.
We conducted ERT (Electric Resistivity Tomography), in addition of GPR (Ground Penetrating Radar) and the seismic refraction survey at the Sarukawa fault in Oga peninsula, northeast of Japan. Especially with the reference to the result of the resistivity structure model across the Sarukawa fault, the important information about the consideration of the subsurface angle of the reverse (thrust) fault is low angle or .high angel.
In this study, ERT survey lines were installed and collected data on September 16, September 26, October 25, and December 7, 2022. Four 235 m long straight survey lines were set up along a farm road in the Iriai-Chuishi area, on the eastern boundary of Iriai lowland, Oga peninsula, Akita prefecture. The Dipole-Dipole and Wenner methods were used for the electrode configuration, with 48 electrodes and 5 m electrode spacing. GNSS positioning was also used for detailed topographic analysis. RES2DINV was used as the analysis software to create a resistivity model of the subsurface within the exploration area.
We can refer the resulted models of the resistivity section across the Sarukawa fault by ERT. General speaking of estimating the location of the dislocation fault surface, we align the thin layer of low resistivity or seek the sharp boundary of resistivity values. Based on the resistivity model (see attached figure), we have two candidates of the buried fault surface of the Sarukawa fault. One is low angle model and the other is high angle model. It is easier to take the low angle model in the subsurface image of surficial soil like as the soften alluvial fan or sand dune deposit in the background of regional stress in the direction of east-west in the northeast of Japan. At present we can refer the 20 m boring result at the site. In the assumption of the low angel fault, the dislocation has to recognized in the boring core but we can not see such kind of rupture in the sand dune in the sample of the core.
So far we tentatively concluded the dislocation angle to the ground surface of the Sarukawa fault is high. But we feel the further investigation is necessary in consideration of detailed topography, rheology and elasticity of the geology, stress and strain of this region etc.
We conducted ERT (Electric Resistivity Tomography), in addition of GPR (Ground Penetrating Radar) and the seismic refraction survey at the Sarukawa fault in Oga peninsula, northeast of Japan. Especially with the reference to the result of the resistivity structure model across the Sarukawa fault, the important information about the consideration of the subsurface angle of the reverse (thrust) fault is low angle or .high angel.
In this study, ERT survey lines were installed and collected data on September 16, September 26, October 25, and December 7, 2022. Four 235 m long straight survey lines were set up along a farm road in the Iriai-Chuishi area, on the eastern boundary of Iriai lowland, Oga peninsula, Akita prefecture. The Dipole-Dipole and Wenner methods were used for the electrode configuration, with 48 electrodes and 5 m electrode spacing. GNSS positioning was also used for detailed topographic analysis. RES2DINV was used as the analysis software to create a resistivity model of the subsurface within the exploration area.
We can refer the resulted models of the resistivity section across the Sarukawa fault by ERT. General speaking of estimating the location of the dislocation fault surface, we align the thin layer of low resistivity or seek the sharp boundary of resistivity values. Based on the resistivity model (see attached figure), we have two candidates of the buried fault surface of the Sarukawa fault. One is low angle model and the other is high angle model. It is easier to take the low angle model in the subsurface image of surficial soil like as the soften alluvial fan or sand dune deposit in the background of regional stress in the direction of east-west in the northeast of Japan. At present we can refer the 20 m boring result at the site. In the assumption of the low angel fault, the dislocation has to recognized in the boring core but we can not see such kind of rupture in the sand dune in the sample of the core.
So far we tentatively concluded the dislocation angle to the ground surface of the Sarukawa fault is high. But we feel the further investigation is necessary in consideration of detailed topography, rheology and elasticity of the geology, stress and strain of this region etc.