• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.165-180
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• 2005

Impact seismic wave test is a method for nondestructive testing of concrete structure using of stress wave which is propagated and reflected from internal flaws within concrete structure and external surface, In this study, we performed non-destructive testing using impact seismic wave test for safety diagnosis of civil engineering structures. For this, I've compared and analized the result in the way of reflective method mostly using on one-dimension such as tunnel lining, and penetration method using the way of cross hole and tomography.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.05a
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• pp.129-136
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• 2005

The groundwater survey was carried out by electrical resistivity and resistivity tomography using several kinds of electrode array to delineate the depth of the saturated zone and basement complex, the aquifer system of fractured rock, and the 2-D resistivity structure was obtained by inversion technique. And the hole-to-surface and crosshole tomography were applied for two boreholes and the inverted resistivity tomogram are obtained. The comparison of those data with core logging data was performed and those results were relatively well correlated. And it was possible to find out the configuration of basement and the fracture zone and the aquifer system from the 2-D resistivity structure and resistivity tomogram.

• The Journal of Engineering Geology
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• v.6 no.1
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• pp.15-22
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• 1996

Frequency content of seismic waves observed in field seismic survey in Korea has almost not exceeded 4kHz(wave length 1m). The limited frequency content not only restricts the minimum size of objects which can be surveyed in seismic tomogrpahic application, but also makes a fundamental limit in the resolution of tomogram. This paper shows the resonable result obtained by confirmimg and resolving the problems which can be occured m measuring procedure for the small - sized section through field application. Seismic tomographic field survey was performed for a concrete construction for railroad bridge in Korea, and to this the tomographic measurements for the stone-build foundation construction for a bell house of church in Germany were compared.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.64-70
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• 1998

Diffraction tomography (DT) is a quantitative technique for high resolution subsurface imaging. In general DT algorithm is used for crosswell imaging. In this study high resolution GPR DT algorithm which is able to reconstruct high resolution image of subsurface structures in multi-monostatic geometry is developed. Developed algorithm is applied to finite difference data and its criteria of application and its limit are studied. Inversion parameters (number of imaging frequency, regularization factor, frequency range) are deduced from isolated weak scattering model. And the usuability of the algorithm is proved by applying to models which break the weak scattering approximation.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.18-24
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• 2017

We performed seismic imaging based on relative S-wave travel times to examine S-wave velocity of upper mantle structure beneath East Asia. We used teleseismic events recorded at 129 broadband stations of the Korea Institute of Geoscience and Mineral Resources (KIGAM), Korea Meteorological Administration (KMA), and National Research Institute for Earth Science and Disaster Prevention (NIED). Relative travel time residuals were obtained by a multi-channel cross-correlation method designed to automatically determine accurate relative phase arrival times. The resulting images show high-velocity anomalies along plate boundaries around the Japanese islands region. These anomalies may indicate subducting Pacific and Philippine Sea plates. On the other hand, a low-velocity anomaly is revealed beneath east of the Korean peninsula down to around 300 km depth, which is thought to be related to the formation of the Ulleung basin and the Ulleung island. Low-velocity anomalies revealed beneath the Jeju island may imply that the formation and volcanism of the Jeju island have been caused by magmatic sources from the deep mantle.

• Geophysics and Geophysical Exploration
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• v.9 no.1
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• pp.44-49
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• 2006

In this study, the resolution capabilities of electrical resistivity tomography (ERT) in the monitoring of $CO_2$ injection are investigated. The pole-pole and bipole-bipole electrode configuration types are used between two uncased boreholes straddling the $CO_2$ plume. Forward responses for an initial pre-injection model and three models for subsequent stages of $CO_2$ injection are calculated for the two different electrode configuration types, noise is added and the theoretical data are inverted with both L1- and L2-norm optimisation. The results show that $CO_2$ volumes over a certain threshold can be detected with confidence. The L1-norm proved superior to the L2-norm in most instances. Normalisation of the inverted models with the pre-injection inverse model gives good images of the regions of changing resistivity, and an integrated measure of the total change in resistivity proves to be a valid measure of the total injected volume.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.140-145
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• 2011

In order to analyze the influence of the noise on a cross-well traveltime tomography to detect a small scale low velocity body in a homogeneous medium, the first arrival travel times were computed one a tunnel model by a finite-difference ray tracing scheme. Three different types and four different intensity levels of white noises were added to the computed first arrival travel times, and velocity tomograms were constructed using an iterative inversion method (SIRT). Tomograms with the noise intensity up to 10% of the maximum traveltime delay in the tunnel model, showed the exact location of the tunnel. However, the velocity shown at the tunnel location was not close to air velocity but only slightly less than the velocity of the background medium. The additive random noise showed significantly less degree of influence on the resulting tomogram than the source- and receiver consistent noise.

• Geophysics and Geophysical Exploration
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• v.6 no.2
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• pp.95-100
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• 2003

In this study, we developed reflection tomography inversion algorithm using Straight Ray Technique (SRT) which can calculate travel time easily and fast for complex geological structure. The inversion process begins by setting the initial velocity model as a constant velocity model that hat only impedance boundaries. The inversion process searches a layer-interface structure model that is able to explain the given data satisfactorily by inverting to minimize data misfit. For getting optimal solution, we used Gauss-Newton method that needed constructing the approximate Hessian matrix. We also applied the Marquart-Levenberg regularization method to this inversion process to prevent solution diverging. The ability of the method to resolve typical target structures was tested in a synthetic salt dome inversion. Using the inverted velocity model, we obtained the migration image close to that of the true velocity model.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.41-50
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• 2006

The crustal structure of Korean Peninsula have been investigated by analyzing group velocity dispersion data of surface wave. Cross.correlation of seismic background motions (Campillo and Paul, 2003; Shapiro et al., 2005) has been applied to estimate the short.period Rayleigh. and Love.wave group velocity dispersion characteristics of the region. Standard processing procedures were applied to the cross.correlation, except that signal whitening was used in place of one.bit sampling equalize power in signals from different times. Multiple.filter analysis was used to extract the group velocities from the estimate Green's functions, which were then use to image the spatially varying dispersion at periods between 0.5 and 20 seconds. The tomographic inversion technique used inverted all periods simultaneously to provide a smooth dispersion curve as a function of period in addition to the usual smooth spatial image for a given period. The Gyeongsang Basin in the southeastern part of the peninsula is clearly resolved with lower group velocities.

• The Journal of Engineering Geology
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• v.16 no.4 s.50
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• pp.327-335
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• 2006

Three processing strategies of seismic refraction data are tested in terms of velocity and depth profiles or structures for mapping of geological discontinuities: GRM(generalized reciprocal method), GLI(generalized linear inversion), Tomography. The test data used in this study are the shot gathers reconstructed by numerical modeling for the structures of 3 planar layers(horizontal, inclined), the buried vertical fracture zones, and vertical fault zones. Tomography is shown to be very efficient for mapping of more complicated tone such as vertical fault and buried fracture zones, whereas GRM and GLI can be useful for horizontal and/or inclined layers, probably on their bases of analysis of first arrivals in travel time curves.