• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.93-99
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• 1999

조화진동하는 점진원에 의한 반무한 탄성체의 응답해석을 수행해 탄성체의 임의의 깊이에서의 응답을 나타내는 계산식을 유도했다 이결과는 최근 연구개발이 진행되고 있는 조화진원에 의한 정밀 지하구조탐사에 중요한 이론적 바탕이 된다. 먼저 실용상 중요한 수평가진에 의한 응답을 계산했다 표면에 큰 응답이 표면파의 형태로 발생하지만 수평진원의 에너지 방사형태는 지향성을 가지고 있어 진원아래의 원뿔형의 영역이 크게 여기된다는 사실을 밝혔다.

• 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.15 no.2
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• pp.85-91
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• 2012

Multiple Lapse Time Window (MLTW) analysis for obtaining intrinsic attenuation value require numerous data without directional bias to compensate focal mechanism. The first window of MLTW, therefore, shows large deviation in fitting smoothed theoretical curve. The information on the focal mechanism may reduce burdens of number and distribution. This study combined algorithm of computing focal mechanism to DSMC method by Yoshimoto (2000). However, the MLTW method based on the numerous data was not applicable to this study, because of the limited data to the almost same fault plane solution. This study showed that the available data was too insufficient to construct smoothed theoretical curve, although the deviation of the first window was improved. Instead of conventional solution by more data, the study seems to be needed for new constraints to obtain smoothed curve.

• Geophysics and Geophysical Exploration
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• v.21 no.2
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• pp.125-131
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• 2018

2017 Pohang earthquake (M 5.4) was more disastrous than 2016 Gyeongju earthquake (M 5.8), partly because of its shallow focal depth. However, precise focal depth of Pohang earthquake is still controversial. Close crustal model showed 6 ~ 11.5 km in relocation depth, whereas other models showed almost surface range. Geothermal study indicated temperature of $300^{\circ}C$ at depth of 7.5 km. Related with observations of seismogenic layer, the focal depth of Pohang earthquake seems to be 7 km depth as obtained by close model.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.293-299
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• 2013

The recent Multiple Lapse Time Window (MLTW) analysis of Korean Peninsula event showed that the focal depth was far greater influence factor than the velocity structure of the model, applying the analysis of the direct simulation Monte Carlo (DSMC) method. Thus, using the events with focal depth of about 10 km, this study considered 330 paths connecting 41 events and 71 stations, and re-examined uniform and depth-dependent velocity models previously studied. As a result, the residual of misfit function greatly decrease from analytic model to DSMC model, reflecting variation of the focal depth from 0 to 10 km. On the other hand, the difference of residuals for each velocity model were relatively small.

• Geophysics and Geophysical Exploration
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• v.20 no.1
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• pp.49-55
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• 2017

Hypocentral depths of 103 aftershocks of the 12 September 2016 Gyeongju earthquake (ML 5.8) were inverted by epicentral relocation, using HYPO71 and HYPOINVERSE. From the comparison of seven models that reflect regional velocity structure in the southern Korean Peninsula, HYPO71 with linear weighting over the whole range showed less residuals than HYPOINVERSE for the model near the epicenter. Less uncertainties of focal depths were observed for the events with large magnitude and short range of the closest S-phase distance.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.862-874
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• 1989

A phase evil method and spectrum analysis were instrument error which is originated from measurement system and the form error of standard specimens. An instrument with a rotating table supported by an air bearing is calibrated using standard specimens. The phase of standard specimens was measured 12 times on the rotating table with rotating 30 in turn and its measurement magnification was set by 100000 times. As a result of data analysis of all the observations, read out at each of 144 orientations(per 2.5) from recorded datafiles, the error of the performance of the instrument and those of the standard specimens are evaluated and a systematic deviation of the instrument is determined. In the particular instrument used in the present experiment, the deviation of the instrument is determined with the accuracy of 15nm and those of standard specimens with the accuracy of 23, 13 n, respectively. The reproducibility of the instrument is investigated, too. If the instrument is calibrated by using the above standard specimens, then the accuracy of the measurement of roundness error can be improved to about 15nm.

• Geophysics and Geophysical Exploration
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• v.19 no.1
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• pp.1-10
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• 2016

The hypocenter distribution of microseismic events generated by hydraulic fracturing for shale gas development provides essential information for understanding characteristics of fracture network. In this study, we evaluate how inaccurate velocity models influence the inversion results of two widely used location programs, hypoellipse and hypoDD, which are developed based on an iterative linear inversion. We assume that 98 stations are densely located inside the circle with a radius of 4 km and 5 artificial hypocenter sets (S0 ~ S4) are located from the center of the network to the south with 1 km interval. Each hypocenter set contains 25 events placed on the plane. To quantify accuracies of the inversion results, we defined 6 parameters: difference between average hypocenters of assumed and inverted locations, $d_1$; ratio of assumed and inverted areas estimated by hypocenters, r; difference between dip of the reference plane and the best fitting plane for determined hypocenters, ${\theta}$; difference between strike of the reference plane and the best fitting plane for determined hypocenters, ${\phi}$; root-mean-square distance between hypocenters and the best fitting plane, $d_2$; root-mean-square error in horizontal direction on the best fitting plane, $d_3$. Synthetic travel times are calculated for the reference model having 1D layered structure and the inaccurate velocity model for the inversion is constructed by using normal distribution with standard deviations of 0.1, 0.2, and 0.3 km/s, respectively, with respect to the reference model. The parameters $d_1$, r, ${\theta}$, and $d_2$ show positive correlation with the level of velocity perturbations, but the others are not sensitive to the perturbations except S4, which is located at the outer boundary of the network. In cases of S0, S1, S2, and S3, hypoellipse and hypoDD provide similar results for $d_1$. However, for other parameters, hypoDD shows much better results and errors of locations can be reduced by about several meters regardless of the level of perturbations. In light of the purpose to understand the characteristics of hydraulic fracturing, $1{\sigma}$ error of velocity structure should be under 0.2 km/s in hypoellipse and 0.3 km/s in hypoDD.

• Journal of the KSME
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• v.26 no.3
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• pp.195-199
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• 1986

지금까지의 해설과 같이, 3-조오 척의 조오- 공작물사이의 접촉상태는 가공물의 정도와 진선도 및 채터 안정성에 직접적인 영향을 주고 있다. 일반적으로 긴 접촉길이를 갖는 완전접촉상티는 선접촉이나 중심선접촉상태보다도 2∼4배 가량의 가공정도나 진원도 향상을 가져오며, 채터 안 정성에 있어서도 현저한 진전을 나타낸다. 따라서 선삭시에 클램핑 접촉상태는 가공물정도나 진원도를 해석하는 과정에서 중요한 인자로서 취급되어야 할 것이며, 구체적인 해석적 과정을 갖지 않고서 원활한 가공결과에 접근하기 위해서는 완전접촉의 상태로서 비교적 접촉 길이를 공작물 반경에 가깝도록 하는 것이 바람직하다고 볼 수 있다.

• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.814-816
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• 2002

최근 급증하고 있는 인터넷 사용자들을 위한 인터 서비스 업체들의 증가와 더불어 악의적인 공격자의공격 또한 증가하고 있다. 이러한 공격으로 인한 인터넷 업체들에게 치명적일 수 있는 신용에 대한 불신임과 서비스의 불안정이라는 피해는 기업의 이미지를 실추시키는 등 막대한 영향을 끼칠 수도 있다. 이러한 악의적인 공격 형태 중 가장 최근 가장 빈번하게 그리고 큰 피해를 주는 공격형태가 DoS(Denial-of-Service)[1]공격이다. 그러나 DoS공격에 대한 적당한 대응방법이 아직까지 미비한 상태이고, 공격에 대응하여 방어한다고 해도 그 진원지를 찾아내지 못한다면 추후 동일한 공격자(attack)에 의해 재차 공격을 받을 가능성을 배제할 수 없는 실정이다. 이에 본 논문은 DoS공격에 대한 적당한 대응하는 하나의 방법으로 공격 경로(attack path)를 찾아내고 더 나아가 공격 진원지(attack origin)의 MAC address를 알아냄으로써 공격의 진원지를 찾아내는 방법을 제안한다.