• Geophysics and Geophysical Exploration
• /
• v.4 no.3
• /
• pp.80-83
• /
• 2001

Four seismic reflection horizons in 3-D seismic data, coherence derived from the seismic data, and 38 well logs from the Boonsville Gas Filed in Texas were tried to be integrated and visualized in 3 dimensions. Time surface was constructed from pick times of the reflection horizons. Average velocities to each horizon at 38 well locations were calculated based on depth markers from the well logs and time picks from the 3-D seismic data. The time surface was transformed to depth surface through velocity interpolation. Coherence was calculated on the 3-D seismic data by semblance method. Spatial distribution of the coherence is captured easily in 3-D visualization. Comparing to a time-slice of seismic data, distinctive stratigraphic features could be correctly recognized on the 3-D visualization.

• Geophysics and Geophysical Exploration
• /
• v.9 no.4
• /
• pp.255-260
• /
• 2006

Measurements in two adjacent (about 1.5 m separation) boreholes reveal that there is a significant degree of variations in the width and property (permeability) of shear zones in the granitic rock. A high frequency (>10 kHz) cross-well seismic tomography was conducted to characterize the features of permeability distribution at the shear zones in the inter-well region. At the shear zones, the correlation between the permeability at the well location and the velocity pattern shown in the cross-well velocity tomogram suggests that a high resolution velocity tomogram may provide useful information for the shear zone characteristics, such as permeability, fracture density, width, and length.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2006.06a
• /
• pp.233-237
• /
• 2006

3D travel time tomography was conducted to characterize the subsuface structure in the valley area. In this study, an area($200m{\times}200m$), where borehole informations were available to aid in the interpretation, was covered with wide source/receiver coverage. In data acquisition, both hole to hole and reverse VSP array was employed. For the inversion, 3D seismic traveltime tomography algorithm based on Fresnel volume was implemented. When compared 3D velocity cube with the geological survey and drilling logs, both results were matched well. From this, we concluded that 3D seismic travel time tomography has enough potential to the field application.

• Tunnel and Underground Space
• /
• v.21 no.6
• /
• pp.460-470
• /
• 2011

Wave velocity was measured to define the weathering characteristics of rock and the strength evaluation of weathered rock on a target of the Aso gravestones with various sizes under the natural environment. As a result, the size correction method which was changed sample of the different size to one of the same size for evaluating wave velocity was proposed, and also suggested the NET (Normalized Elapsed Time) as a new weathering index of rock. In addition, the strength of the weathered rock was estimated from the weathering classification of rock using the NET. Wave velocity of welded tuff was high and didn't show velocity degradation, on the other hand, one of andesite was low and showed velocity degradation. The degree of weathering between rocks of the different size is considered to be comparable, applying the NET based on the on the $V_p/V_o$-NET curve. Furthermore, the classification of rock weathering stages using the NET based on the $S_c/S_o$-NET curve was available, and the estimation of strength for the weathered rock was also possible.

• Geophysics and Geophysical Exploration
• /
• v.26 no.2
• /
• pp.84-93
• /
• 2023

The supervised learning-based deep-learning seismic inversion techniques have demonstrated successful performance in synthetic data examples targeting small-scale areas. The supervised learning-based deep-learning seismic inversion uses time-domain wavefields as input and subsurface velocity models as output. Because the time-domain wavefields contain various types of wave information, the data size is considerably large. Therefore, research applying supervised learning-based deep-learning seismic inversion trained with a significant amount of field-scale data has not yet been conducted. In this study, we predict subsurface velocity models using Laplace-domain wavefields as input instead of time-domain wavefields to apply a supervised learning-based deep-learning seismic inversion technique to field-scale data. Using Laplace-domain wavefields instead of time-domain wavefields significantly reduces the size of the input data, thereby accelerating the neural network training, although the resolution of the results is reduced. Additionally, a large grid interval can be used to efficiently predict the velocity model of the field data size, and the results obtained can be used as the initial model for subsequent inversions. The neural network is trained using only synthetic data by generating a massive synthetic velocity model and Laplace-domain wavefields of the same size as the field-scale data. In addition, we adopt a towed-streamer acquisition geometry to simulate a marine seismic survey. Testing the trained network on numerical examples using the test data and a benchmark model yielded appropriate background velocity models.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.17 no.4
• /
• pp.227-236
• /
• 1997

Quantitative analysis and imaging of elastic wave propagation are very important for the materials evaluation as well as flaw detection. The elastic wave propagation in an anisotropic media is more complex, and analysis and imaging become essential for flaw detection and materials evaluation. In the anisotropic media, the wave velocity is dependent on the propagation direction. In addition, the direction of group velocity is different from that of phase velocity, the direction of energy flow is not same as the propagation direction of wavefront (beam skewing effect). Especially, this effect becomes critical for the large anisotropic media such as fiber composite materials, and the results using elastic waves for those materials have to be analyzed considering the wave propagation mechanism. Since the analytical approach for the wave propagation in the anisotropic materials is limited, the numerical analysis such as finite difference method (FDM) have been used for these case. Therefore, 2-dimensional FDM program for the elastic wave propagation is developed, and wave propagation in anisotropic media are simulated.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.09a
• /
• pp.43-54
• /
• 2005

Care should be taken when performing the P and S wave velocity loggings. Some of them are the effect of casing that is installed to prevent the borehole collapsing when the drilling is done on the loose ground such as soil and/or soft rock, and the discrepancy of the velocities of the same media according to the difference of the source wave frequency spectrum. To overcome these difficulties, the following suggestions are recommended; (1) try a careful drilling technique that can eliminate the necessity of the casing, and (2) apply the logging methods with the proper frequency spectrum that is appropriate to the object of the velocity logging.

• Journal of the Korean earth science society
• /
• v.21 no.3
• /
• pp.349-358
• /
• 2000

Compressional and shear wave velocities (Vp and Vs) and densities have been measured for serpentinite, amphibolite, amphibole and biotite schist, and gneiss from western part of Chungnam Province at room temperature. Ranges of the density are 2.6${\sim}$2.86g/cm$^3$ for serpentinite, 2.25${\sim}$2.81g/cm$^3$ for talc, and 2.74${\sim}$3.07g/cm$^3$ for metamorphic rocks. Of these rocks, talc shows wider ranges than serpentinite and amphibolites due to its metamorphic process from serpentinite. Values of Vp and Vs are 5719${\sim}$6062m/s and 2898${\sim}$3351m/s for serpentinites, 4019${\sim}$5478m/s and 2241/${\sim}$2976m/s for talc, 5375${\sim}$6372m/s and 3042${\sim}$3625m/s for amphibolite, 5290${\sim}$5499m/s and 2968${\sim}$3137m/s for schist, and 4788m/s and 2804m/s for gneiss, respectively. Velocity of P wave increases 1.47 times faster than S wave with increase of density. The results of seismic velocity measurement show anisotropy, higher velocity across than along the schistocity of rocks, especially in metamorphic rocks. This fact indicates that there were regional metamorphism related with tectonic forces. Values of seismic velocity increase with increasing pressure from 20 MPa to 70 MPa, especially in metamorphic rocks. Overall recalculated Vp and Vs values suggest that the serpentinite indicates for upper mantle in the respects of seismic characteristics, in spite of high degree of serpentinization. In addition, those of the amphibolite do for low crust, and gneiss and schist for upper crust.

• The Journal of Engineering Geology
• /
• v.12 no.1
• /
• pp.89-93
• /
• 2002

Seismic geotomography method was performed to verify rock-filled settlement and its stability in No.38+0 profile and No.40+0 profile. The velocity distributions of geotomography method expressed the quantitative value of the ground conditions. The rock-filled layer and in-situ sediments layer are clearly divided on the basis of seismic velocity 2100 m/sec which is derived from the results of seismic geotomography and boring. Current rock-filled settlement conditions are somewhat different from designed settlement estimation line. Seismic geotomography represents current settlement conditions as a quantitative analysis.

• Journal of the Korean GEO-environmental Society
• /
• v.3 no.3
• /
• pp.5-13
• /
• 2002

In tunnel design, geotechnical survey of over 200m tunnel depth is required because of its characteristical topography. For this reason, there are difficulties in collecting information of basic data in tunnel design because of large-scale costs in borehole tests, of limits to a geotechnical analysis by the existing refraction seismic survey and of analytical errors in steep mountainous area. Seismic tomography has many advantages as follows; 1) seismic velocity as absolute value is more reliable than electrical resistivity, 2) geotechnical analysis in deep tunnel depth is available by seismic velocity, 3) analytical errors is reduced in steep mountainous area. In this paper, it was found out a correlation of seismic velocity and Q in tunnel design in the neighborhood of the National Capital region and the reduction effect of tunnel construction cost using reliable rock quality by seismic tomography compared with by borehole data and electricity resistivity data.