• Geophysics and Geophysical Exploration
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• v.7 no.3
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• pp.164-173
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• 2004

To delineate geothermal water movement at the Pohang geothermal development site, Self-Potential (SP) survey and monitoring were carried out during pumping tests. Before drilling, background SP data have been gathered to figure out overall potential distribution of the site. The pumping test was performed in two separate periods: 24 hours in December 2003 and 72 hours in March 2004. SP monitoring started several days before the pumping tests with a 128-channel automatic recording system. The background SP survey showed a clear positive anomaly at the northern part of the boreholes, which may be interpreted as an up-flow Bone of the deep geothermal water due to electrokinetic potential generated by hydrothermal circulation. The first and second SP monitoring during the pumping tests performed to figure out the fluid flow in the geothermal reservoir but it was not easy to see clear variations of SP due to pumping and pumping stop. Since the area is covered by some 360 m-thick tertiary sediments with very low electrical resistivity (less than 10 ohm-m), the electrokinetic potential due to deep groundwater flow resulted in being seriously attenuated on the surface. However, when we compared the variation of SP with that of groundwater level and temperature of pumping water, we could identify some areas responsible to the pumping. Dominant SP changes are observed in the south-west part of the boreholes during both the preliminary and long-term pumping periods, where 3-D magnetotelluric survey showed low-resistivity anomaly at the depth of $600m\~1,000m$. Overall analysis suggests that there exist hydraulic connection through the southwestern part to the pumping well.

• Geophysics and Geophysical Exploration
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• v.13 no.4
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• pp.407-415
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• 2010

MT soundings were carried out in 2008, in northern Victoria, Australia, as a continuing collaboration research of 2007 between Republic of Korea, Australia, and Japan. The main purpose of this research is to investigate electrical conductivity structure and thus help understanding of tectonic structure in central Victoria, which is believed to be closely linked to mineralization and magmatic processes of this region. The survey area is located in western Lachlan Fold Belts, which is the part of Tasman Fold Belts in southeastern Australia. An MT profile of 2008 is almost parallel to the one of 2007 and approximately 50 km away. The 2D inversion result of MT data also shows that the position of conductivity discontinuity near surface are well matched with the positions of major faults, such as Avoca Fault, which is the structural boundary between Stawell and Bendigo Zones, and Heathcote Fault Zone, which marks the boundary between Bendigo and Melbourne Zones. It is also confirmed from resistivity image that internal faults in Bendigo Zone are in listric form, which is implied to be formed by structural shortening during compressional orogenic activity in Silurian.