• The Journal of Engineering Geology
• /
• v.15 no.1
• /
• pp.19-27
• /
• 2005

The Sambo mine is located in Hae-je Myeon, Moo-an Gun, Chollanamdo, which consists of host gneiss and rhyolite possessing quartzite veins with other compositions such as gold, silver, and sublimated sulfur. The ore grade estimated from the core was 0.05～10.9g/t or less in gold and 0.05～389g/t or less in silver, indicating a partial mineralization. The purpose of this paper is to understand the subsurface structures and the distribution of mineralized bodies in the Sambo mine using a combined method of Schlumberger, Wenner, and Dipole-di-pole resistivity surveys on the surface and the resistivity tomography survey in boreholes. The result of three-dimensional resistivity inversion showed that the mineralized body is extended to 240m long in the N10°～20°E direction, with 30m wide and 80 m thick from the surface. The low resistivity zones (<1,000ohm-m) determined from the resistivity image were in good agreement with the mineralized bodies and weak zones identified from the logged cores.

• Geophysics and Geophysical Exploration
• /
• v.7 no.1
• /
• pp.80-87
• /
• 2004

During excavation work for the construction of a highway bridge in a limestone area in Korea, several cavities were found, and construction work was stopped temporarily. Cavities under the bridge piers might seriously threaten the safety of the planned bridge, because they could lead to excessive subsidence and differential settlement of the pier foundations. In order to establish a method for reinforcement of the pier foundations, borehole radar reflection and tomography surveys were carried out, to locate cavities under the planned pier locations and to determine their sizes where they exist. Since travel time data from the crosshole radar survey showed anisotropy, we applied an anisotropic tomography inversion algorithm assuming heterogeneous elliptic anisotropy, in order to reconstruct three kinds of tomograms: tomograms of maximum and minimum velocities, and of the direction of the symmetry axis. The distribution of maximum velocity matched core logging results better than that of the minimum velocity. The degree of anisotropy, defined by the normalized difference between maximum and minimum velocities, was helpful in deciding whether an anomalous zone in a tomogram was a cavity or not. By careful examination of borehole radar reflection and tomography images, the spatial distributions of cavities were delineated, and most of them were interpreted as being filled with clay and/or water. All the interpretation results implied that two faults imaged clearly by a DC resistivity survey were among the most important factors controlling the groundwater movement in the survey area, and therefore were closely related to the development of cavities. The method of reinforcement of the pier foundations was based on the interpretation results, and the results were confirmed when construction work was resumed.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2008.10a
• /
• pp.137-140
• /
• 2008

During CHAOS (2003, 2006) and SSGH projects (2007), acoustic investigation including hydroacoustic (HA), side-scan sonar (SSS) and highresolution sparker seismic (HSS) surveys was carried out on the northeastern Sakhalin slope ($53^{\circ}56'\;N$, $143^{\circ}52'\;E$ to $54^{\circ}40'\;N$, $144^{\circ}32'\;E$). More than 130 methane seeps with high backscatter intensity are identified on SSS mosaic, which are well accompanied with gas flares in the water column on HA profiles and subbottom gas chimneys on HSS profiles. It is likely that that some seeps align along a NW strike parallel to the Lavrentiev Fault.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2008.10a
• /
• pp.125-130
• /
• 2008

Electrical resistivity and seismic refraction surveys were conducted to investigate geologic structures and geotechnical characteristics of the subsurface in Dok-do island, along with rock physical properties. The resistivity results in Seo-do island show that the fault adjacent to the fisherman's shelter is a normal fault and extended towards the NW direction. Bedded Rapilli Tuff in the downstream was more severely influenced in depth by weathering and erosion than Trachy Andesite II in the upstream area. The physical properties of the rocks illustrate that Trachyte and Trachy Andesite are hardest, Massive Tuff Breccia is next, and Tuffs are the most soft rocks in Dok-do island.

• Geophysics and Geophysical Exploration
• /
• v.4 no.2
• /
• pp.34-44
• /
• 2001

Forward modeling by construction of synthetic data is usually practiced in a horizontal surface and a few subsurface structures. However, in-situ surveys often take place in such topographic changes that the corrupted field data always make it difficult to interpret the right signals. To examine the propagation characteristic of elastic waves on the irregular surface, a general mesh generation code for finite element method was modified to consider the topography. By implementing this algorithm, the time domain modeling was practiced in some models with surface topography such as mound, channel, etc. The synthetic data obtained by receivers placed on surface also agreed with the analytic solution. The snapshots showing the total wave-field revealed the propagation characteristic of the elastic waves through complex subsurface structures and helped to identify the signals on the time traces. The transmission of Rayleigh waves along the surface, compressive waves, and sheer waves was observed. Moreover, it turned out that the Rayleigh waves behave like a new source at the edge.

• Geophysics and Geophysical Exploration
• /
• v.14 no.3
• /
• pp.185-190
• /
• 2011

In marine controlled-source electromagnetic (CSEM) modeling, it may be difficult to evaluate primary fields accurately using conventional linear filters because they decay very rapidly with distance. However, since there exists a closed-form solution to the Hankel transform in TM mode for a homogeneous half space, we can assess the accuracy of linear filters for evaluating the Hankel transform. As a result, only nine out of 36 source-receiver pairs show that EM fields decrease linearly in semi-log scale with an increase of source-receiver distance, while EM fields are either 0 or not reduced significantly due to an effect of the air layer. There also exist closed-form solutions for the nine pairs, and the others can be evaluated accurately with a relatively short filter. This paper proposes a method which uses closed-form solutions for TM-mode Hankel transforms and a filter with 61 coefficients for TE-mode ones.

• Journal of the Korean Geophysical Society
• /
• v.4 no.1
• /
• pp.71-84
• /
• 2001

A study was initiated to investigate whether the groundwaters being discharged into the sea could be used as a possible water resources. This paper presents a preliminary information about the groundwaters being discharged along the shoreline of East Sea. Major discharge sites were selected primarily on the basis of the informaion on surface temperatures of the sea. Hydrogeologic and geographic conditions were also considered in selecting the major discharge sites. The development possibility of the discharging groundwater were estimated roughly, considering populations, industries and social development compatibilities of the selected areas. Groundwater dams and linked usage with surface water were suggested as possible development methods for the groundwaters.. Based on this study, we selected about 60 sites as the major discharge areas and tentatively recommended 6 sites as optimal sites for development of groundwaters being discharged into the sea. However, detailed in-situ hydrogeologic surveys are required prior to the final decision.

• Korean Journal of Heritage: History & Science
• /
• v.46 no.4
• /
• pp.4-23
• /
• 2013

Songsalli Ancient Tombs of Gongju consists of seven tombs. King Muryeong's tomb, the seventh tomb, is a brick chamber tomb discovered during the drainage works for the fifth and the sixth tombs in 1971. The excavation at the time focused on topographic surveys of the tomb entrance and the inside of the burial chamber as well as collection of the remains. The burial mount survey confirmed the status of some stone slab remaining and lime-mixed soil layers, but the survey did not examine the exterior structure of the whole tomb as the mounds were removed even more deeply. The excavation revealed damages to the bricks and mural damages due to moisture and fungus in the sixth and the seventh tombs. Between 1996 and 1997, Gongju National University conducted a comprehensive detailed survey of Songsalli Ancient Tombs including a geophysical survey, with an aim to identify the root causes of such degradation. Based on the results, repair took place in 1999 and the fifth, sixth and seventh tombs were placed under permanent conservation to conserve the cultural assets. General public is currently denied access. The purpose of this study was to conduct a three-dimensional resistivity and GPR surveys on the ground surface of the fifth, sixth and seventh tombs of Songsalli Ancient Tombs in order to understand the underground status after repair. The study also aimed to understand the thickness of all the tomb walls and exterior structure based on GPR inside King Muryeong's tomb. The exploration on the ground surface found that the three tombs and soil adjacent to the tombs had resistivity as low as 5 to $90{\Omega}m$, which confirmed that the soil water content was still as high as that prior to the repair work. Additionally, GPR found that the wall construction of the burial chamber of King Muryeong's tomb was approximately 70cm in thickness, while the structure was of 2B with two bricks, about 35cm in length, put together longitudinally(2B brick masonry). The pathway to the burial chamber was of the 2B structure just like that of the burial chamber walls, while its thickness was 80cm with an eyebrow-type arch connected to it. Also, the ceiling exterior appears to have an arch structure, identical to the shape inside.

• Economic and Environmental Geology
• /
• v.30 no.2
• /
• pp.137-142
• /
• 1997

At the tailings dam of the disused Brukunga pyrite mine in South Australia, reaction of groundwater with the tailings causes the formation and discharge of sulphuric acid. There is a need to improve remediation efforts by decreasing groundwater flow through the tailings dam. Geophysical methods have been investigated to determine whether they can be used to characterise variations in depth to watertable and map preferred groundwater flow paths. Three methods were used: transient electromagnetic (TEM) soundings, direct current (DC) soundings and profiling, and self potential (SP) profiling. The profiling methods were used to map the areal extent of a given response, while soundings was used to determine the variation in response with depth. The results of the geophysical surveys show that the voltages measured with SP profiling are small and it is hard to determine any preferred channels of groundwater flow from SP data alone. Results obtained from TEM and DC soundings, show that the DC method is useful for determining layer boundaries at shallow depths (less than about 10 m), while the TEM method can resolve deeper structures. Joint use of TEM and DC data gives a more complete and accurate geoelectric section. The TEM and DC measurements have enabled accurate determination of depth to groundwater. For soundings centred at piezometers, this depth is consistent with the measured watertable level in the corresponding piezometer. A map of the watertable level produced from all the TEM and DC soundings at the site shows that the shallowest level is at a depth of about 1 m, and occurs at the southeast of the site, while the deepest watertable level (about 17 m) occurs at the northwest part of the site. The results indicate that a possible source of groundwater occurs at the southeast area of the dam, and the aquifer thickness varies between 6 and 13 m. A map of the variation of resistivity of the aquifer has also been produced from the TEM and DC data. This map shows that the least resistive (i.e., most conductive) section of the aquifer occurs in the northeast of the site, while the most resistive part of the aquifer occurs in the southeast. These results are interpreted to indicate a source of fresh (resistive) groundwater in the southeast of the site, with a possible further source of conductive groundwater in the northeast.

• Geophysics and Geophysical Exploration
• /
• v.8 no.1
• /
• pp.67-72
• /
• 2005

To investigate the feasibility of a new concept of storing Liquefied Natural Gas (LNG) in a lined hard rock cavern, and to develop essential technologies for constructing underground LNG storage facilities, a small pilot plant storing liquid nitrogen (LN2) has been constructed at the Korea Institute of Geoscience and Mineral Resources (KIGAM). The LN2 stored in the cavern will subject the host rock around the cavern to very low temperatures, which is expected to cause the development of an ice ring and the change of ground condition around the storage cavern. To investigate and monitor changes in ground conditions at this pilot plant site, geophysical, hydrogeological, and rock mechanical investigations were carried out. In particular, geophysical methods including borehole radar and three-dimensional (3D) resistivity surveys were used to identify and monitor the development of an ice ring, and other possible changes in ground conditions resulting from the very low temperature of LN2 in the storage tank. We acquired 3D resistivity data before and after storing the LN2, and the results were compared. From the 3D images obtained during the three phases of the resistivity monitoring survey, we delineated zones of distinct resistivity changes that are closely related to the storage of LN2. In these results, we observed a decrease in resistivity at the eastern part of the storage cavern. Comparing the hydrogeological data and Joint patterns around the storage cavern, we interpret this change in resistivity to result from changes in the groundwater flow pattern. Freezing of the host rock by the very low temperature of LN2 causes a drastic change in the hydrogeological conditions and groundwater flow patterns in this pilot plant.