• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.49-55
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• 2006

The purpose of the present study is to analyse characteristics of the background noise for the broadband seismic stations in KMA. It is well known that the background noise arises continuously from long period microseism, sea waves, minute changes of atmospheric pressure, seasonal temperature change of the ground surface, culture activities, and etc. The background noise shows spatial and temporal changes and it has various characteristics such as its spectral amplitudes in frequency domain are not constant Such the background noise gives considerable influences on the quality of seismic record. To investigate annual variations, the background noise was separated into high frequency components of above 1Hz More larger average amplitude is found in winter than other seasons. The average amplitude for 12 seismic stations are compared. It is known that the background noise is considerably larger in stations located in island region such as Jeju, Ulleungdo, and Bagryeongdo seismic stations. However the noise is relatively small in inland stations such as Chuncheon, Chungju and Uljin seismic stations.

• Earthquakes and Structures
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• 제9권5호
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• pp.983-997
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• 2015

This research evaluates the soil conditions for seismic stations situated in Romania using the horizontal-to-vertical spectral ratio (HVSR). The strong ground motion database assembled for this study consists of 179 analogue and digital strong ground motion recordings from four intermediate-depth Vrancea seismic events with $M_w{\geq}6.0$. In the first step of the analysis, the influence of the earthquake magnitude and source-to-site distance on the H/V curves is evaluated. Significant influences from both the earthquake magnitude and hypocentral distance are found especially for soil class A sites. Next, a site classification method proposed in the literature is applied for each seismic station and the soil classes are compared with those obtained from borehole data and from the topographic slope method. In addition, the success and error rates of this method are computed and compared with other studies from the literature. A more in-depth analysis of the H/V results is performed using data from seismic stations in Bucharest and a comparison of the free-field and borehole H/V curves is done for three seismic stations. The results show large differences between the free-field and the borehole curves. As a conclusion, the results from this study represent an intermediary step in the evaluation of the soil conditions for seismic stations in Romania and the need to perform more detailed soil classification analysis is highly emphasized.

• Earthquakes and Structures
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• 제23권1호
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• pp.101-113
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• 2022

A new type of fabricated subway station construction technology can effectively solve these problems. For a new type of metro structure form, it is necessary to clarify its mechanical properties, especially the seismic performance. A soil-structure elastoplastic finite element model is established to perform three-dimensional nonlinear dynamic time-history analysis based on the first fabricated station structure-Yuanjiadian station of Changchun Metro Line 2, China. Firstly, the nonlinear seismic response characteristics of the fabricated and cast-in-place subway stations under different seismic wave excitations are compared and analyzed. Then, a comprehensive analysis of several important parameters that may affect the seismic response of fabricated subway stations is given. The results show that the maximum plastic strain, the interlayer deformation, and the internal force of fabricated station structures are smaller than that of cast-in-place structure, which indicates that the fabricated station structure has good deformation coordination capability and mechanical properties. The seismic responses of fabricated stations were mainly affected by the soil-structure stiffness ratio, the soil inertia effect, and earthquake load conditions rarely mentioned in cast-in-place stations. The critical parameters have little effect on the interlayer deformation but significantly affect the joints' opening distance and contact stress, which can be used as the evaluation index of the seismic performance of fabricated station structures. The presented results can better understand the seismic responses and guide the seismic design of the fabricated station.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.49-56
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• 2000

Instrumental observation of earth quakes in KIGAM was first attempted in the earty 1980`s by using 6 portable seismographs in the vicinity of Yang-San Faults. Now twenty-four permanent stations, which are equipped with short-period or broad-band seismometer, are included in seismic research network in KIGAM, including KSRS array station in Wonju which is consisted of 26 bore-hole stations. The seismic network of KIGAM is also linked to that of KEPRI(Korea Electric Power Research Institute)which is consisted of eight stations installed within and around the nuclear power plants. Owing to real-time data acquisition by telemetry, it became feasible to automatically locate hypocenters of the local events within fifteen minutes by computer data processing system, named KEMS(Korea Earthquake Monitoring System). Results of the hypocenter determination, together with observational data, are compiled and stored in the data base system. And they are published via web site whose URL is http://quake.kigam.re.kr KIGAM is also running t재 permanent geomagnetic stations installed in Daejun and Kyungju. The observed geomagnetic data are transmitted to Earthquake Research Centre in KIGAM by seismic network and compiled for the purpose of earthquake prediction research and other basic geophysical research.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2009년도 학술대회 초록집
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• pp.54-59
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• 2009

지진 관측소의 지진 관측 능력은 관측소의 잡음 수준에 좌우되어 잡음 수준이 높은 관측소는 작은 규모의 지진 또는 원거리의 지진에 의한 약한 지반 진동을 감지하기 어렵다. 그러므로 지진관측망의 지진 관측 능력을 고려하기 위해서는 지진관측소의 분포뿐만 아니라 각 관측소의 잡음 수준을 고려해야 한다. 대부분의 국내 지진관측소는 1 Hz 이상의 주파수 대역에서 인간의 활동에 의한 영향을 받고 있으며, 이로 인해 주간과 야간의 잡음 수준 차이가 나타난다. 이러한 잡음 변화에 따른 지진 관측 능력의 차이와 분포를 살펴보기 위해 2005년부터 2007년까지 한국지질자원연구원과 기상청에서 운영하는 광대역 관측소 30개소의 잡음 분석 결과를 이용하였다. 각 관측소의 잡음 수준을 고려하였을 때 야간에는 규모 2.4 정도 이상의 지진이 내륙에서 발생한 것을 관측할 수 있는 반면, 주간에는 규모 2.6 정도의 지진 관측 능력을 보였다.

• 터널과지하공간
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• 제16권6호
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• pp.486-494
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• 2006

주파수 영역에서 H/V 스펙트럼비를 구하는 방법은 부지 지반증폭함수를 평가할 때 자주 사용되는 방법이다. 이 방법은 Nakamura에 의해 처음으로 제시되었으며 주로 표면파를 이용하였다. 본 논문에서는 H/V 스펙트럼비를 분석한 결과를 이용하여 국내에 분포되어 있는 지진관측소 부지의 지반증폭 특성을 분석하였으며 이를 위해 본진을 포함한 12개의 후쿠오카 지진으로부터 관측된 지반진동 자료가 이용되었다. 분석결과 대부분의 지진관측소의 H/V 스펙트럼비는 저주파수 영역에서는 변화가 거의 없는 지반증폭 특성을 보여주었다. 하지만 고주파수 영역의 H/V 스펙트럼비는 지진관측소에 따라 우세 주파수 및 1개 또는 여러 개의 지역 피크값을 가지고 있는 것과 같이 특징적인 지반증폭 특성을 보여 주었다. 물론 지반증폭 특성 자체도 부지에 대해 중요한 정보를 제고한다는 점에서 중요하지만 관측된 지반진동 자료를 이용하여 지진원 및 지각감쇠 특성 요소를 분석할 경우 결과값의 왜곡을 피하기 위해 지반증폭 특성을 제거할 필요가 있다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.61-68
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• 2003

The H/V ratio (Horizontal to Vertical spectral ratio) has been used to infer site amplification without previous knowledge of near-surface geology and in fact may provide useful general site condition information. This method is used to classify the site characteristics of seismic stations in Korea by comparison with known H/V ratios representative of various sites all over the world. In addition, differences between horizontal and vertical kappa values were evaluated for each seismic stations by comparing WV ratio and Weak Motion amplification derived from inversion of stochastic ground motion parameters and were used as index to quantitatively classify the site characteristics.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.12-15
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• 2003

Korea Institute of Geoscience and Mineral Resources(KIGAM) is operating Wonju Korea Seismic Research Station(KSRS), 29 regional seismic research stations and 5 Korea-China joint seismic stations in China. Also KIGAM is operating Korea Earthquake Monitoring System (KEMS) to archive the real-time data stream and to determine event parameters (epicenter, origin time, and magnitude) by the automatic processing and analyst review. To do this, KEMS used KIGAM's regional seismic network and other institute's network in a near real-time base. From Dec. 1, 2001 to Nov. 30, 2002, 3,827 seismic events were analyzed in a automatic processing procedure and finally 3,437 events were analyzed by analyst and archived. But problem is this event catalog includes not only natural earthquake, but also artificial events produced by the blast. More than 80 % events were concentrated in daytime and many events were concentrated in the confirmed blast sites, Pyeongyang, Pocheon, Yeongjong-do, Donghae city, etc. Because these artificial events are a major potential cause of error when estimating the seismicity of a specific region, discrimination procedure has to be developed in the first place.

• 한국지구과학회지
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• 제30권7호
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• pp.810-823
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• 2009

지진원 상수의 정밀한 결정과 지진재해의 예측에 있어서 결정적인 요인의 하나는 부지증폭 특성에 관한 상세한 정보이다. 한반도 광대역 지진관측소의 부지증폭 특성이 0.2-20 Hz 범위 내에서 주파수의 함수로 추정되었다. 한반도 남부에서 2003년부터 2008년까지 관측된 43개의 지진에 대한 총 1275개의 지진기록이 사용되었다. 지진동 모델의 역산으로부터 추정된 28개소의 관측소에 대한 부지증폭비는 수직대 수평(H/V) 스펙트럼비로부터 얻어진 증폭비와 몇몇 관측소를 제외하고는 대체로 그 값이 일치하는 것이 발견되었다. 이 연구에서 얻어진 주파수별 부지증폭 특성은 어떤 뚜렷한 공간분포를 보이지 않았다. 또한 부지증폭 특성은 기반암 종류보다는 풍화의 정도와 크게 관련이 있는 것으로 나타났다. 주파수별 부지증폭비를 참조하여 28개소의 광대역 관측소를 4개의 그룹으로 나누었고, 그룹별 특징에 대하여 본문에 서술하였다.

• 한국지진공학회논문집
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• 제23권6호
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• pp.321-327
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• 2019

We performed seismic noise level analysis to access the proper functioning of 11 newly established seismic stations in the southeastern region of Korea. One-hour long segments of seismograms were selected from the continuous data of the 3 elements for 61 days from March 1, 2019. For each segment of data, the power spectral density (PSD) was estimated from the continuous back ground noise data of the 3 elements for periods ranging from 0.02~100 s. The median noise levels (NLs) of the stations were compared with the new noise model (NNM) of USGS and NLs of station TJN installed in a tunnel on a granite basement. We observed that the NLs of the newly installed seismometers were between the upper and lower limit of the NNM. In a comparison with the noise level of station TJN, the new seismometers had their own noteworthy features. The NLs from accelerometers (Epi-sensors) were ~ 40 dB higher than the NLs from velocimeters (STS-sensors) for periods > 10 s, which is because the small and light Epi-sensors are sensitive to environmental changes. Daily and weekly variations in spectral noise level were observed clearly in short periods < 1 s, and these are considered to be related to human activities. The seismometers in boreholes showed ~20 dB weaker NLs in the cultural noise band. The NLs of accelerometers at a depth of 30 m were also much lower by 30 dB for long periods > 10 sec. Overall the functioning of the new velocimeter and accelerometer stations was reliable for periods ranging from 0.02~100 s and 0.02~10 s, respectively.