• Geophysics and Geophysical Exploration
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• v.25 no.1
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• pp.1-13
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• 2022

For surveying shallow gas reservoirs in the Pohang basin, we proposed a seismic exploration method applicable to the transition zone in which land and marine areas are connected. We designed the seismic acquisition geometry considering both environments. We installed land nodal receivers on the ground and employed vibroseis and airgun sources in both land and marine areas. For seismic exploration in the transition zone, specific acquisition and processing techniques are required to ensure precise matching of reflectors at the boundary between the onshore and offshore regions. To enhance the continuity of reflection events on the seismic section, we performed amplitude and phase corrections with respect to the source types and applied a static correction. Following these processing steps, we obtained a seismic section showing connected reflectors around the boundary in the transition zone. We anticipate that our proposed seismic exploration method can also be used for fault detection in the transition zone.

• Geophysics and Geophysical Exploration
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• v.11 no.3
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• pp.197-203
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• 2008

A shallow high-resolution seismic reflection survey was carried out at the Mineopo tidal flat on the western coast of Korea. The purpose of the survey was to investigate shallow sedimentary structure of the tidal flat associated with the recent sea level change. A total of 795 shots were generated at 1 m interval from a 5-kg hammer source and recorded on 48 channels of 100 Hz geophones along two mutually perpendicular profiles. The water-saturated ground condition resulted in suppressed ground rolls by significantly decreasing rigidity. In addition, seismic velocities over 1500 m/s provided easy segregation of reflected arrivals from lower velocity noise. As a consequence, seismic sections from the study area show significantly higher resolution and signal to noise ratio than conventional land seismic sections. The tidal flat consists of 5 sedimentary sequences above acoustic basement. The seismic sections reveal the continuous structure of the tidal flat formed in association with sea level rise during the Holocene.

• Geophysics and Geophysical Exploration
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• v.19 no.3
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• pp.164-173
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• 2016

Cable-free seismic technology is to acquire seismic data with independent receivers which are not connected by cables. This is an effective method for survey designs with less topographical conditions. With technology advancement for cable-free receivers, reliable data quality, easy deployment, and picking up the receivers, the cable-free technology has begun to apply to land seismic acquisition. In this study we introduced a cable-free seismic system and its equipment. We tried to build up the cable-free seismic technology through the field application. In the seismic tomography field applications, the seismic signals of the cable-free receiver and cabled receiver with the same distance from the source show the same phase in early stage. The difference of the first arrival times between two signals is less than 0.4 ms, which could be accepted. In the field application for seismic reflection exploration, we acquired shot gathers with different source depth and dynamite charge. The shot gathers from cable-free and cabled system are similar to each other. With an efficient method for receiver deployment and survey design, the application of the cable-free technology will increase.

• Geophysics and Geophysical Exploration
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• v.4 no.4
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• pp.133-144
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• 2001

An effective seismic reflection technique for mapping the cavities and bedrock surface in carbonate rocks is described. The high resolution seismic reflection images were successfully registered by using the hydrophones employed in the stream-water driven trench, and were effectively focused by applying optimal data processing sequences. The strategy included enhancement of the signal interfered with the large-amplitude scattering noise, through pre- and post stack processing such as time-variant filtering, bad-trace editing, residual statics, velocity analysis, and careful muting after NMO (normal moveout) correction. The major reflections including the bedrock surface were mapped with the desired resolution and were correlated to the seismic crosshole tomographic data. Shallow major reflectors could be identified and analyzed on the AGC (auto gain control)-applied field records. Three subhorizontal layers were identified with their distinct velocities; overburden (<3000 m/s), sediments (3000-4000 m/s), limestone bedrock (>4000 m/s). Taking into account of no diffraction effects in the field records, gravel-rich overburdens and sediments are considered to be well sorted. Based on the images mapped consistently on the whole survey line and seismic velocity increasing with depth, this area probably lacks in sizable cavities (if any, no air-filled cavities).

• Proceedings of the KSRS Conference
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• 2005.10a
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• pp.325-328
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• 2005

To estimate presumptive local ground subsidence area near Abandoned Under ground Coal Mine(AUCM) at Samcheok city in Korea, the geological properties of existing ground subsidence area and the geophysical prospecting data were analyzed using GIS. The electrical resistivity survey and seismic reflection survey database were constructed from investigation reports and factors which are related with ground subsidence such as geological map, topological map, land use map, lineament map, groundwater level, RMR (Rock Mass Rating), mining tunnel map and slope database were constructed also to make a comparative study of each parameters. As a result of the spatial analysis of existing ground subsidence area, 9 major factors causing ground subsidence were extracted and a connection between the structure of underground and the ground subsidence was determined from the analysis of geophysical prospecting data. The estimation of presumptive ground subsidence area was performed using the correlation between the result from neural network analysis of 9 factors and the scrutiny of geophysical prospecting data.

• The Korean Journal of Petroleum Geology
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• v.7 no.1_2 s.8
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• pp.7-12
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• 1999

A new high-resolution rnagnetotelluric (MT) survey was conducted for pull-apart basin analysis (Cretaceous Eumsung Basin), combined with surface sedimentological results. Two cross-basinal MT profiles represent an asymmetric form with a subbasin in the southeastern part. These basinal architectures are well compatible with paleoflow directions and facies transitions of surface sedimentology. The results also suggest that the basin fills reflect pull-apart opening with rapid subsidence of the central blocks. Combined with the surface sedimentological data on asymmetric lithofacies distribution, facies transitions, and paleoflow directions of the alluvio-lacustrine systems, the MT data help explain basin-fill processes during the basin formation. For petroleum exploration and basin analysis, the high-frequency MT technique can be a useful substitute for the costly burden of a seismic-reflection survey on land.