• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.54-59
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• 2009

Seismic station of high noise level has difficulties detecting relatively weak ground motions due to small earthquakes or teleseismic events because earthquake detectability of seismic station depends on seismic noise level. To figure out the capability of earthquake detection of a seismic network, therefore, seismic noise level of each station also needs to be considered, including the distribution of seismic stations. Recently, it has been known that most of broadband seismic stations in South Korea have affected by cultural noise in the frequencies higher than 1 Hz and show diurnal variations of noise level. In order to analyze the effect of diurnal variation of seismic noise level on earthquake detectability, we used the result of background seismic noise level analysis of seismograms of 30 broadband stations of KIGAM and KMA from 2005 to 2007. This study shows that earthquakes greater than magnitude 2.4 occurring within the Korean Peninsula can be detected at night while those greater than magnitude 2.6 can be detected in the daytime.

• Economic and Environmental Geology
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• v.36 no.3
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• pp.201-212
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• 2003

Recently, the ability of earthquake detection in the Kyungsang Basin of southeastern Korean Peninsula is greatly improved since seismic stations including seismic network of KIGAM(Korea Institute of Geoscience and Mineral Resources) have been significantly increased. However, a large number of signals from explosions are recorded because of frequent medium to large chemical explosions. The discrimination between natural earthquakes and explosions in the Basin has become an important issue. High frequency local records from 43 earthquakes and 43 explosions with comparable magnitude are selected to establish a reliable discrimination technique in the Basin. Several discrimination techniques in spectral domain using spectral amplitude ratios among Pg, Sg, and Lg waves are widely examined with tile selected data. Among them the Pg/Lg spectral ratio method is appeared to be a good discrimination technique to improve the discrimination power. Multivariate discriminant analysis is also applied to the Pg/Lg spectral ratios. The discrimination power of the Pg/Lg ratios for distance corrected three component record compared to uncorrected vertical component one shows distinct improvement. In the frequency band 4 to 14 Hz, Pg/Lg spectral ratio for distance corrected three component record provides discrimination power with a total misclassification probability of only 0.89%.

• Geophysics and Geophysical Exploration
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• v.16 no.1
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• pp.53-58
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• 2013

It was introduced a seismic mini-array that could monitor microseismicity efficiently and analyzed seismic data obtained from the mini-array that was operated from December 19, 2012 to January 9, 2013. The mini-array consisted of a six channel data logger, a central 3 components seismometer, and a tripartite array of vertical sensors centered around the 3 components seismometer as an equilateral triangle with about 100 m aperture. All seismometers that had the same instrument response were connected a 6 channel data logger, which was set to record seismograms at a sampling rate of 200 sps. During the three weeks of campaign, a total of 16 microearthquakes were detected. Using time differences of P wave arrivals from the vertical components, S-P time from 3 components seismometers, and back azimuth from the seismic array analysis, it was possible to locate the hypocenter of the microearthquake even with one seismic miniarray. The epicenters of two nearest microearthquakes were a quarry site located 1.3 km from the mini-array. The records of quarry blasting confirmed the our analysis.

• Journal of the Korea Society of Computer and Information
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• v.14 no.2
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• pp.37-44
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• 2009

In this paper, we propose an efficient method which improves the performance of transmission of PGA which is essential data for real-time earthquake monitoring system. Currently, above 120 earthquake stations were installed nationwide and additional installation is expected because the social interesting of earthquake hazard is rising. Real-time earthquake monitoring system checks earthquake occurrence by using PGA were calculated from acceleration data of each seismic station. An efficient method of PGA data transmission is key factor of real-time monitoring. The key idea of proposed method is to deal with each seismic station using an unique ID, to assign one bit to indicate whether a packet include a station's data or not. Proposed method can contain more station data and decrease the data loss compared to current method. To verify proposed method, we investigate the turnaround time and ratio of data loss using above 91000 packets. As results of experiment. the proposed method is proven that the method need more time about 50% but reduce the data loss about 87% as compared to previous method.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.203-210
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• 2013

To look into site characteristics of the Hwacheon borehole seismic station, we analyzed property of earthquake and microtremor recorded on surface and borehole seismometers. Acoording to analysis result of microtremor, the surface-to-borehole energy ratio was approximately 15 times greater during the daytime than during the nighttime, and the surface-to-borehole ratios of spectral amplitudes as frequency increases. For earthquake data, amplitude spectra and dominant frequency were computed using surface and borehole data. As a result, small earthquakes with short distance recorded on surface seismometer peaked at 8 Hz, 46 Hz. This result corresponds to resonance frequencies (7.4 Hz, 46 Hz) calculated by H/V spectral ratio. We confirmed amplification effect by site characteristics of overburden. Background noise level was approximately 20,000 times smaller at borehole seismic station than surface seismic station. These results provide strong evidence for the superior recording of earthquakes using borehole seismometers instead of surface seismometers.

• Geophysics and Geophysical Exploration
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• v.14 no.4
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• pp.267-273
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• 2011

A cluster of micro-earthquakes in the transition zone between the continental and oceanic crust in the East Sea was relocated using the Joint Hypocenter Determination (JHD) method. In order to increase the number of available earthquakes and to take advantage of the high detection capability of the Korea National Seismic Network (KNSN), continuously recorded seismic data were reviewed to identify 56 micro-earthquakes occurring in a 20 km ${\times}$ 20 km region. The initial earthquake hypocenters were determined using a routine single event location method. Single event locations do not reveal any significant structures in the study area. After relocating the earthquake hypocenters using the JHD technique, the earthquakes were clustered and four potential faults responsible for earthquake generation in the subsurface were delineated. They are defined by two sub-vertical and two steeply south-dipping seismicities located next to each other.

• Geophysics and Geophysical Exploration
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• v.17 no.3
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• pp.137-146
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• 2014

This study presents a procedure for discrimination of artificial events from earthquakes occurred in and around the Korean Peninsula using data set in the Wonju KSRS seismograph network, Korea. Two training sets representing natural and artificial earthquakes were constructed with 150 and 56 events, respectively, with high signal to noise ratio. A frequency band, Pg(4-6 Hz)/Lg(5-7 Hz), which is optimal for the discrimination of seismic sources was derived from the two-dimensional grid of Pg/Lg spectral amplitude ratio. The corrections for the effects of earthquake magnitude and hypocentral distance were carried out for improvement of discrimination capability. For correcting the effect of magnitude dependence due to the inverse proportionality of corner frequency to seismic moment, the Brune's source spectrum was subtracted from the observation spectrum. The spectrum was corrected using the optimal damping coefficient to remove damping effect with the hypocentral distance. The effect of locally varying spectrum ratio was cancelled correcting variation of wave propagation along the ray path. The performance in discrimination between training sets of natural and artificial events was compared using the Mahalanobis distance in each step of correction. The procedure of magnitude, distance, and path corrections show clear improvements of the discrimination results with increasing Mahalanobis distance, from 1.98 to 3.01, between two training sets.

• Geophysics and Geophysical Exploration
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• v.26 no.4
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• pp.268-274
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• 2023

Finite source inversion is performed with a Green's function matrix and geodetic coseismic displacement. Conventionally, the Green's function matrix is constructed using the Okada model (Okada, 1985). However, for more realistic earthquake simulations, recent research has widely adopted the physics-based model, which can consider various material properties such as elasticity, viscoelasticity, and elastoplasticity. We used the physics-based software PyLith, which is suitable for earthquake modeling. However, the PyLith does not provide a mesh generator, which makes it difficult to perform finite source inversions that require numerous subfaults and observation points within the model. Therefore, in this study, we developed CPInterface (COMSOL-PyLith Interface) to improve the convenience of finite source inversion by combining the processes of creating a numerical model including sub-faults and observation points, simulating earthquake modeling, and constructing a Green's function matrix. CPInterface combines the grid generator of COMSOL with PyLith to generate the Green's function matrix automatically. CPInterface controls model and fault information with simple parameters. In addition, elastic subsurface anomalies and GPS observations can be placed flexibly in the model. CPInterface is expected to enhance the accessibility of physics-based finite source inversions by automatically generating the Green's function matrix.

• Economic and Environmental Geology
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• v.53 no.3
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• pp.321-336
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• 2020

The Headquarters for Earthquake Research Promotion (HERP) represents the upper-most level of Japan's earthquake disaster prevention governance. Its policy committee establishes the national earthquake investigation research promotion plan. The earthquake investigation committee of HERP collects survey geo-data and evaluates the research results of each earthquake disaster prevention agency. The establishment of an earthquake-related geo-resilience research strategy is both necessary and desirable for Korea. The concept of geo-resilience entails the ability to improve disaster resilience through the application of research results and the convergence of geoscience with science and technology (S&T) including the humanities and social sciences. The achievement of geo-resilience requires a national long-term roadmap and strategy for earthquake prediction research, the development of earthquake disaster prediction and prevention technology, Geo-ICT convergence technology development, implementation of a geocyber physics system (Geo-CPS), the use of geo-mimetics, and geoscientific R&D as it relates to local communities. Through such efforts, the national research institutes of Korea will be able to develop earthquake prediction capacities in relevant fields, reinforce proactive response capabilities, enhance community-level confidence in geodata and its research results, foster next-generation geoscientific manpower, and expand geoscientific infrastructure.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.279-279
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• 2021

위성영상정보는 센서의 종류, 취득, 분석, 재난과 위성영상 특성 매칭 등의 제약으로 재난 상황에서 제한적으로 사용되었다. 일반적으로 인공위성의 종류는 탑재한 센서의 정보제공 능력 범위에 따라 분류 가능하며 이에 따라 대상 범위가 결정된다. 본 연구에서는 재난의 예측, 탐지, 사후처리를 위한 위성자료의 취득과 활용을 위해 다양한 위성과 탑재된 센서의 궤도, 공간 해상도, 파장대 등의 특성에 대하여 분석하고 재난유형별로 최적 위성영상을 선정하였다. 행정안전부에서는 재난과 재해의 유형을 자연재난(10종)과 사회재난(27종)으로 분류하였다. 위성영상 활용이 가능한 재난 유형은 가시적으로 확인이 가능한 자연재난에 해당하며 그 중 태풍, 홍수, 가뭄, 산불 등 총 4종의 재난유형별로 가용한 최적의 위성영상을 분석하였다. 재난관측에 사용 가능한 대표적인 탑재체의 종류는 극궤도 지구관측 위성에서 광학과 SAR로 구분할 수 있다. 각 기본 특성에 따라 제공되는 정보의 종류가 분류되며 광학 센서는 태양복사 및 지구복사에너지 파장 영역 중 가시광선-근적외선-단파적외선-열적외선 파장대 영역의 분광 정보를 제공할 수 있는 다중 밴드들로 구성된다. 지표의 특정 대상이나 물질을 탐지하고 변화를 감지·분석하는데 유용하여 홍수, 태풍, 지진 등 자연 및 사회 재난·재해 관측에 유용하게 이용된다. SAR 센서는 장파장의 전자기파를 방출한 후 돌아오는 신호를 활용하여 대상에 대한 정보를 획득한다. 대기의 효과 및 요소를 투과하는 주파수 대역별 장파장 밴드 정보를 활용하여 고해상도의 대상 표면, 위치, 형태 등의 정보를 측량 및 관측하므로 중·광역 지역에 제약 없이 영상정보를 획득할 수 있어 산사태, 홍수, 지진, 등의 재난 모니터링에 유용하다. 이러한 다종 위성별 센서들의 특징(공간 해상도, 파장대별 밴드 특성, 관측폭, 재방문 주기 등)들을 분석하여 재난유형별로 가용한 무료/상용 지구관측위성을 분류한 결과 태풍에는 광역관측, 정지궤도 위성, 홍수에는 광학 및 SAR 고해상도 위성, 가뭄은 광역관측, 다분광 광학 위성 그리고 산불에는 정지궤도, 광학, SAR 위성이 적합함을 알 수 있다.