• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.57-65
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• 2000

파형분석과 두 점을 잇는 파선추적은 진원요소 결정의 정확성을 향상시키는 주요한 요인이다. 본 연구에서는 3성분 지진기록의 직선형도(rectilinearity) 함수와 방향성(directionality)함수를 사용하여 파형분석한 결과와 두 점을 잇는 파선추적을 기존의 진원요소결정 프로그램에 적용하여 진원요소 결정의 정확성을 증가시켰다. 지진의 규모가 작을 때 Pn이 보이지 않고 PmP가 초동파로 기록된 것처럼 보인다. 이러한 지진에서는 주어진 진앙거리에서 최소 주행시간이 걸리는 P파와 S파의 초동파만 사용한 기존의 진원요소 결정 방법과 본 연구에서 PmP와 SmS를 사용한 결과는 매우 큰 차이를 보인다.

• Geophysics and Geophysical Exploration
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• v.11 no.4
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• pp.361-367
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• 2008

When constructing a synthetic seismogram in the earthquake study or in seismic data interpretation by using a ray-tracing technique, the most troublesome and error-prone task is to define a suite of ray codes for the corresponding rays to trace in advance. An infinite number of rays exist for any arbitrarily located source and receiver in a medium. Missing certain important rays or an inappropriate selection of ray codes in tracing rays may result in wrong interpretation of the earthquake record or seismogram. Automatic ray code generation could be able to eliminate those problems. In this study we have developed an efficient algorithm with which one can generate systematically all the ray codes for the source(s) and receiver(s) arbitrarily located in a model. The result of this work could be used not only in analysing multiples in seismic data processing and interpretation, but also in coda wave study, study on the amplification effects in a basin and phase identification of the waves multiply reflected/refracted in earthquake study.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.5
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• pp.57-61
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• 2001

This study introduces an algorithm for determination of hypocentral parameters using phase analysis and two-point ray tracing to enhance accuracy and stability of computations. When the magnitude of earthquake is relatively small(usually $m_{b}$<3.2), the PmP phase which looks like the first arrival phase may be observed without observing the Pn phase. In this case, the hypocentral parameters calculated by the existing method using the first arrival of P and S phases and by the method developed in this study using PmP and SmS phases show large differences. The computational results of determination of hypocentral parameters for actual earthquake events show that this method gives much smaller rms errors than the existing methods do.o.

• Proceedings of the Korean Geotechical Society Conference
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• 1996.10a
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• pp.203-208
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• 1996

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.167-173
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• 1999

Since the resolution of the 2-D hole-to-hole seismic traveltime tomography is affected by the limited ray transmission angle, various methods were used to improve the resolution. Linear traveltime interpolation(LTI) ray tracing method was chosen for forward-modeling method. Inversion results using the LTI method were compared with those using the other ray tracing methods. As an inversion algorithm, SIRT method was used. In the iterative non-linear inversion method, the cost of ray tracing is quite expensive. To reduce the cost, each raypath was stored and the inversion was performed from this information. Using the proposed method, fast convergence was achieved. Inversion results are likely to be affected by the initial velocity guess, especially when the ray transmission angle was limited. To provide a good initial guess for the inversion, generalized regression neural network(GRNN) method was used. When the transmitted raypath angle is not limited or the geological model is very complex, the inversion results are not affected by initial velocity model very much. Since the raypath angles, however, are limited in most geophysical tomographic problems, the enhancement of resolution in tomography can be achieved by providing a proper initial velocity model by another inversion algorithm such as GRNN.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.55-62
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• 2000

In constructing a synthetic seismogram using ray-tracing method a suite of ray-code is required to obtain a realistic seismogram which is similar to the actual seismogram or earthquake record under consideration. An infinite number of rays exist for any arbitrarily located source and receiver. One select only a finite number of such rays in computing a synthetic seismogram so their selection becomes important to the validity of the seismogram being generated. Missing certain important rays or an inappropriate selection of ray-codes in tracing rays may result in wrong interpretation of the earthquake record or seismogram. Automatic ray-code generation will eliminate such problems. In this study we have developed an efficient algorithm, with which one can generate systemastically all the ray-codes connecting source and receiver arbitrarily located. The result of this work will helpful in analysing multiple reflections in seismic data processing as well as simulating Lg wave and multiply reflected or converted phases in earthquake study.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.1
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• pp.19-24
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• 1997

The seismic of the main shock and two after shocks of the Yeongwol Earthquake are studied based on the phase analysis. The travel time curves and two point ray tracing with 12 different possible phases are used to analyze the phases of the records, which were provided by KIGAM seismic network. The results of phase analysis of the Yeongwol Earthquake show the characteristics as follows 1) The main shock ($M_s$=4.5) clearly shows Pn phase but two after shocks ($M_s$=3.8 and $M_s$=2.5) do not show Pn phase. 2) The Pg PmP looks as first arrival phase in the after shock records whose epicentral distance is smaller or larger than 145 km, 3). It is very difficult to identify the phases in the seismic records, which ae related to the Conrad discontinulty, even if the Conrad discontiulty exists. 4) The record of GRE station located outside of the Kyeongsan Basin shows different arrival time of Pn phase, P-S duration time and frequency comared with those of the other stations located within the Kyeongsan Basin.

• 한국방재학회:학술대회논문집
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• 2009.02b
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• pp.61.2-61.2
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• 2009

• Journal of Korea Water Resources Association
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• v.54 no.1
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• pp.39-48
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• 2021

The experiment of rip current at successive ends of breaking wave crests was conducted in a laboratory wave basin, and its time-varying evolution according to incident wave durations was observed by using ortho-rectified images. The experiment utilized the generation of a quasi nodal line of the honeycomb-pattern waves (i.e., intersecting wave trains) formed by out-of-phase motion of two piston-type wave makers arranged in the transverse direction, instead of the original honeycomb pattern waves which are generated when two wave trains propagate with slightly different wave directions. The particle moving distance and velocity caused by the rip current were measured by using the particle tracking technique. As a result, the rip current was survived for a while even without incident waves after its generation due to several successive ends of wave crests, and it moved the particles further out to sea.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.69-72
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• 2008

EZTOMO is a crosswell seismic tomography software system. The system has capability of event picking, raytracing, inversion, error analysis, and visualization of the processing results. Waveform of the first arrival signal has been utilized to select the event of the first motion, and uncertainty measured in estimation of the first breaks has been utilized to improve the inversion process.