| Title | Interpretation of 3-D Magnetotelluric Data Including Sea Effect for Geothermal Exploration in Pohang, Korea |
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| Authors | Tae Jong Lee, Yoonho Song, Toshihiro Uchida, Yuji Mitsuhata, and Seokhoon Oh |
| Year | 2004 |
| Conference | Asian Geothermal Symposium |
| Keywords | 3-D MT survey, sea effect, geothermal exploration, Pohang geothermal field |
| Abstract | A three dimensional (3-D) magnetotelluric (MT) survey has been made to delineate the subsurface structures and possible fractures for exploration of low temperature geothermal resources in Pohang, Korea. The site is located in southeastern part of Korea and is very close to the east-ward sea shore. Survey area lies in 3 ~ 8 km apart from the sea shore lined to the north/south direction. To infer the sea effect, 3-D MT modeling has been performed for a layered model including the sea water. Layering of the model and conductivities of each layer are roughly estimated by well logs and other geological information. Results showed that the conductive sea water affects the low frequency MT data, especially below 0.2 ~ 1 Hz depending on the distance from the sea shore. Most severe sea effect was observed from the southeast parts of the survey area due to Youngil bay. Two kinds of 3-D inversion have been performed with the MT data observed from the site; including the sea as a constraint in the inversion or not. The two inverted models showed very similar characteristics in shallow parts, roughly down to 2 km. At deeper parts, however, they showed very different characteristics as can be expected from the modeling study. Strong effect of the nearby sea seems to form a fictitious conductive structure in southeast part of the survey region in ordinary 3-D inversion. A conductive structure, however, was shown at about 3 km depth from both of the inversions. More geological and geophysical study will be needed to identify the structure. |