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| | Abstract | | Self-potential is electrical potential mainly generated by thermoelectric, chemical and streaming potentials in the subsurface. The flow of groundwater is often recognized as a bigger source of SP and the electrical potential associated with ground-water flow is especially called as streaming-potential. SP is generated by excess electric charge carried by underground stream. In case that underground structure is homogeneous, electrical current density according to ground-water flow becomes uniform. Therefore SP on the surface increases monotonically from upstream to downstream of groundwater flow. However, the anomalous fluctuations of SP start to appear for subsurface inhomogeneous groundwater flow due to the non-uniform conveyance of changes. Most of the past interpretations of observed SP anomaly have not focused on such effects of subsurface inhomogeneity. In this study, we developed a simulation code for the subsurface groundwater flow to accommodate inhomogeneous groundwater flow and to estimate the effects of underground structural anomaly on SP. We found that the anomalies of permeability and of coupling-coefficient in the subsurface are predominant parameters to effectively estimate the distribution of surface SP in the existence of inhomogeneous underground flow. |
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