• Tunnel and Underground Space
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• v.13 no.4
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• pp.279-286
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• 2003

Many trials to set up the correlation between the rock mass classification and the earth resistivity have been carried out to design tunnel support type based on the interpreted electrical resistivity acquired by surface electrical survey. But it is hard to find reports on the comparison of the real rock support type determined during the excavation with the electrical resistivity by the inversion of the survey data acquired before the tunneling. In this study, the rock mass classification based on the face mapping data and the resistivity inversion data are investigated to see if it is possible to design reliably the rock support type based on the surface electrical survey. To get the quantitative correlation, rock engineering indices such as RCR(rock condition rating), N(Rock mass number), Q-system and RMR(rock mass rating) are calculated. Since resistivity data has low resolution, Kriging method as a post processing technique which minimizes the estimated variance is used to improve resolution. The result of correlation analysis shows that the 2D electrical resistivity survey is appropriate to see the general trend of the geology in the sense of rock type, though there might be some local area where these two factors do not coincide. But the correlation between the result of 3D survey and the rock mass classification turns out to be very high, and then 3D electrical resistivity survey can make it possible to set up more reliable rock support type.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.532-541
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• 2016

The objective of this paper is to support accurate pavement condition assessment and decision of proper maintenance method and time by conducting visual inspection and calculating the remaining life of pavement from falling weight deflectometer(FWD) data. Each was implemented in the same long-term performance pavement(LTPP) sections. Visual inspection was executed to measure pavement condition indices such as crack, rutting and international roughness index(IRI) and the Seoul Pavement Index(SPI) was calculated based on these results. The dynamic modulus was back-calculated from the FWD data. The remaining pavement lives were determined from equivalent single axle loading(ESAL) and FWD data. Correlation of maintenance priority by each result value was examined. Consequently, the correlation between remaining life to Crack and Rutting was higher than the other factors or indicesbecause IRI is not related to FWD value and SPI value consists with IRI value and other indices. The R-square value of correlation of FWD with Crack and Rutting was 0.65, which indicated an insufficient correlation. Consequently, when decision of maintenance of method, time, etc. is determined, FWD data have to be considered with Crack and Rutting because of those relations.

• Geophysics and Geophysical Exploration
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• v.6 no.1
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• pp.13-22
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• 2003

TSP (Tunnel Seismic Profiling) survey is a technique for imaging and characterizing geological structures ahead of a tunnel face. The seismic modeling algorithm and the synthetic data could be helpful for TSP surveys. However, there is few algorithm to describe the propagation of the elastic waves around the tunnel. In this study, existing 2-dimensional seismic modeling algorithm using finite element method was modified to make a suitable algorithm for TSP modeling. Using this algorithm, TSP modeling was practiced in some models. And the synthetic data was analyzed to examine the propagation characteristics of the elastic waves. First of all, the modeling for the homogeneous tunnel model was practiced to examine the propagation characteristics of the direct waves in the vicinity of the tunnel. And the algorithm was applied to some models having reflector which is perpendicular or parallel to the excavation direction. From these, the propagation characteristics of the reflected waves were examined. Furthermore, two source-receiver arrays were used in respective models to investigate the properties of the two arrays. These modeling algorithm and synthetic data could be helpful in interpreting TSP survey data, developing inversion algorithm and designing new source-receiver arrays.

• Geophysics and Geophysical Exploration
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• v.7 no.2
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• pp.148-154
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• 2004

This article reviews the development of three-dimensional (3-D) magnetotelluric (MT) modeling. The 3-D modeling of electromagnetic fields is essential in understanding the physics of MT soundings, and in implementing an inversion method to reconstruct a 3-D resistivity image. Although various numerical schemes have been developed over the last two decades, practical methods have been quite limited. However, the recent rapid improvement in computer speed and memory, as well as the advance in iterative solution algorithms for a large system of equations, makes it possible to model the MT responses of complex 3-D structures, which have been very difficult to simulate before. The use of staggered grids in finite difference method has become popular, conserving a magnetic flux and an electric current and allowing for realistic discontinuous fields. The convergence of numerical solutions has been greatly accelerated by adopting Krylov subspace methods, proper preconditioning techniques, and static divergence corrections. The vector finite-element method using edge elements is also free from the discontinuity problem, and seems a natural choice for modeling complex structures including irregular topography because its flexibility allows one to capture full geometric complexity.

• Journal of the Korean earth science society
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• v.30 no.2
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• pp.153-164
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• 2009

We examined the regional 1-D deep resistivity structure of the Korean Peninsula using MT data acquired at seven sites located in the Kyongsang Basin and Kyonggi Massif. At the sites located in the Kyongsang Basin, surrounding sea distorts observed MT response and hence this distortion, so called "sea effect", is corrected using an iterative tensor stripping method. The 1-D layered inversion results for the seven MT sites reveal 4 layered structure, which is composed of 1) near surface layer, 2) upper crust, 3) lower crust and upper mantle, and 4) asthenosphere from the surface downward. Conrad interface, which is a boundary between upper and lower crust, is distinctly identified beneath all the MT sites. Conrad interface depth is estimated to about be 17km in the Kyongsang Basin and about 12km in the Kyonggi Massif, while the upper crust of the Kyongsang Basin is about 5 times more resistive than that of the Kyonggi Massif. Finally, asthenosphere is inferred to exist below a depth of approximately 100km with a resistivity of 200-300 ohm-m.

• Geophysics and Geophysical Exploration
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• v.22 no.1
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• pp.21-28
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• 2019

We perform a 3D tomographic inversion using surface wave dispersion curves to obtain S-velocity model and radial anisotropy beneath Saudi Arabia. The Arabian Peninsula is geologically and topographically divided into a shield and a platform. We used event data with magnitudes larger than 5.5 and epicentral distances shorter than $40^{\circ}$ during 2008 ~ 2014 from the Saudi Geological Survey. We obtained dispersion curves by using the multiple filtering technique after preprocessing the event data. We constructed SH- and SV-velocity models and consequently radial anisotropy model at 10 ~ 60 km depths by inverting Love and Rayleigh group velocity dispersion curves with period ranges of 5 ~ 140 s, respectively. We observe high-velocity anomalies beneath the Arabian shield at 10 ~ 30 km depths and low-velocity anomalies beneath the Arabian platform at 10 km depth in the SV-velocity model. This discrepancy may be caused by the difference between the Arabian shield and the Arabian platform, that is, the Arabian shield was formed in Proterozoic thereby old and cold, while the Arabian platform is covered by predominant Paleozoic, Mesozoic, and Cenozoic sedimentary layers. Also we obtained radial anisotropy by estimating the differences between SH- and SV-velocity models. Positive anisotropy is observed, which may be generated by lateral tension due to the slab pull of subducting slabs along the Zagros belt.

• Geophysics and Geophysical Exploration
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• v.26 no.4
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• pp.229-237
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• 2023

The use of artificial sources such as explosives and mechanical vibrations for seismic exploration in urban areas poses challenges, as the vibrations and noise generated can lead to complaints. As an alternative to artificial sources, the surface waves generated by traffic noise can be used to investigate the subsurface properties of urban areas. However, traffic noise takes the form of plane waves moving continuously at a constant speed. To apply existing surface wave processing/inversion techniques to traffic noise, the recorded data need to be transformed into a virtual shot gather format using seismic interferometry. In this study, various seismic interferometry methods were applied to traffic noise data, and the optimal method was derived by comparing the results in the Radon and F-K domains. Additionally, the data acquired using various receiver arrays were processed using seismic interferometry, and the results were compared and analyzed to determine the most optimal receiver array direction for exploration.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.2
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• pp.82-91
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• 2006

We investigated the possibility of using effluents from a municipal sewage treatment plant (STP) as tracers a tracer for hydrologic studies of rivers. The possibility was checked in a 12-km long reach downstream of Jeonju Municipal Sewage Treatment Plant (JSTP). Time-series monitoring of the water chemistry reveals that chemical compositions of the effluent from the JSTP are fluctuating within a relatively wide range during the sampling period. In addition, the signals from the plant were observed at the downstream stations consecutively with increasing time lags, especially in concentrations of the conservative chemical parameters (concentrations f3r chloride and sulfate, total concentration of major cations, and electric conductivity). Based on this observation, we could estimate the stream flow (Q), velocity (v), and dispersion coefficient (D). A 1-D nonreactive solute-transport model with automated optimization schemes was used for this study. The values of Q, v, and D estimated from this study varied from 6.4 to $9.0m^3/sec$ (at the downstream end of the reach), from 0.06 to 0.10 m/sec, and from 0.7 to $6.4m^2/sec$, respectively. The results show that the effluent from a large-scaled municipal STP frequently provides good, multiple natural tracers far hydrologic studies.

• Journal of the Korean earth science society
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• v.28 no.1
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• pp.64-74
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• 2007

The marine seismic prospecting using a research vessel in the shallow sea near the coastal area has certain limits according to the water depth and survey environment. Also, for the electrical resistivity survey at seashore area, one may need a specially designed high-voltage source to penetrate the very conductive surface layer. Therefore, we have conducted a feasibility study on the application of magnetotelluric method (MT), a passive geophysical method, on investigating of shallow marine environment geology. Our study involves both theoretical modeling and field survey at the tidal flat area which represent the very shallow marine environment. We have applied the audio-frequency magnetotelluric (AMT) method to the intertidal deposits of Gunhung Bay, west coast of Korea, and analysed the field data both qualitatively and quantitatively to investigate the morphology and sedimentary stratigraphy of the tidal flat. The inversion of AMT data well reveals the upper sedimentary layer of Holocene intertidal sediments having a range of 13-20 m thickness and the erosional patterns at the unconformable contact boundary. However, the AMT inversion results tend to overestimate the depth of basement (30-50 m) when compared with the seismic section (27-33 m). Since MT responses are not significantly sensitive to the resistivity of middle layer or the depth of basement, the AMT inversion result for basement may have to be adjusted using the comparison with other geophysical information like seismic section or logging data if possible. But, the AMT method can be an effective alternative choice for investigating the seashore area to get important basic informations such as the depositional environment of the tidal flat, sea-water intrusion and the basement structure near the sea shore.

• Journal of the Korean earth science society
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• v.29 no.1
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• pp.1-12
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• 2008

A geophysical mapping was performed for Hwasan caldera which is located in Euisung Sub-basin of the southeastern part of the Korean Peninsula. In order to overcome the limitation of the previous studies, remote sensing technic was used and dense potential data were obtained and analyzed. First, we analyzed geological lineament for target area using geological map, digital elevation model (DEM) data and satellite imagery. The results were greatly consistent with the previous studies, and showed that N-S and NW-SE direction are the most dominant one in target area. Second, based on the lineament analysis, highly dense gravity data were acquired in Euisung Sub-basin and an integrated interpretation considering air-born magnetic data was made to investigate the regional structure of the target area. The results of power spectrum analysis for the acquired potential data revealed that the subsurface of Euisung Sub-basin have two density discontinuities at about 1 km and 3-5 km depth. A 1 km depth discontinuity is thought as the depth of pyroclastic sedimentary rocks or igneous rocks which were intruded at the ring vent of Hwasan caldera, while a 3-5 km depth discontinuity seems to be associated with the depth of the basin basement. In addition, three-dimensional gravity inversion for the total area of Euisung Sub-basin was carried out, and the inversion results indicated two followings; 1) Cretaceous Palgongsan granite and Bulguksa intrusion rocks, which are located in southeastern part and northeastern part of Euisung Sub-basin, show two major low density anomalies, 2) pyroclastic rocks around Hwasan caldera also have lower density when compared with those of neighborhood regions and are extended to 1.5 km depth. However, a poor vertical resolution of potential survey makes it difficult to accurately delineate the detailed structure caldera which has a vertically developed characteristic in general. To overcome this limitation, integrated analysis was carried out using the magnetotelluric data on the corresponding area with potential data and we could obtain more reasonable geologic structure.