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

• Journal of the Earthquake Engineering Society of Korea
• /
• v.23 no.6
• /
• pp.321-327
• /
• 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.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2000.10a
• /
• pp.41-48
• /
• 2000

We have installed the borehole seismic recording system at Hyodongri in eastern part of Kyungsan Basin, which has the advantages of reduction in noise by human activities and distorting effects of near-surface rocks. Here we describe briefly the borehole seismic station and recording system. And we analyse the characteistics of back ground the station obtained from borehole sensors. The back ground noise level in time domain is about 50~100$\mu$cm/sec. The average curve of noise spectrum is lower than NHNM(New High Noise Model)of GSN(Global Seismic Network)operated by USGS. The results could be useful prior information for study on earthquake records observed at Hydongri station.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.259-262
• /
• 2005

The large transformers used in the electric power company become targets of public complaints because of those characteristics generating high-level noise. Reducing vibration level is the basis of noise control for the large transformers. For this reason, a vibrating reducing element is developed for the large transformers with a sub-element enduring seismic movement. Large attenuation of vibration is achieved by applying the element to the large transformers in a substation.

• Geophysics and Geophysical Exploration
• /
• v.21 no.2
• /
• pp.94-102
• /
• 2018

To characterize virtual reflection images of deep subsurface by the method of seismic interferometry, we analyzed effects of offset range, ambient noise, missing data, and statics on interferograms. For the analyses, seismic energy was simulated to be generated by a 5 Hz point source at the surface. Vertical components of particle velocity were computed at 201 sensor locations at 100 m depths of 1 km intervals by the finite difference method. Each pair of synthetic seismic traces was cross-correlated to generate stacked reflection section by the conventional processing method. Wide-angle reflection problems in reflection interferometry can be minimized by setting a maximum offset range. Ambient noise, missing data, and statics turn to yield processing noise that spreads out from virtual sources due to stretch mutes during normal moveout corrections. The level of processing noise is most sensitive to amplitude and duration time of ambient noise in stacked sections but also affected by number of missing data and the amount of statics.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.6 s.99
• /
• pp.652-659
• /
• 2005

In this paper, seismic qualification analysis for the Plant control Panel is carried out to confirm the structural integrity under the seismic conditions represented by required response spectra(RRS). The finite element method(FEM) is used for the analysis and a mode combination method is adopted to obtain a more reliable spectrum analysis results. In addition, the experimental analysis is performed to compare the reliability of the analytical results. The analysis results shows that the plant control panel system is designed to have the dynamic rigidity with no resonance frequency below 33 Hz. The analytically calculated maximum stress of the plant control panel system is $36\%$ of the field strength of material, thus it can be shown that the system has a stable structure for the seismic load.

• Journal of KSNVE
• /
• v.7 no.1
• /
• pp.33-41
• /
• 1997

To cover a range of possible site conditions where the Korean standard nuclear power plant may be constructed, a range of generic site conditions is selected for geologic and seismologic evaluation. To envelop other Asian countries as well as the Korean peninsula, there is an attempt to increase the seismic level to 0.3g ground motions for the safe shutdown earthquake. The dynamic analyses of the reactor vessel internals and fuel assemblies are performed for the increased motions and the effect of seismic level on the response is investigated. Also the nonlinear response characteristics are discussed by comparing the loads between operating basis earthquake and safe shutdown earthquake excitations. The design adequacy of the reactor vessel internals and fuel assemblies for the increased seismic level is addressed.

• Journal of the Korean GEO-environmental Society
• /
• v.24 no.2
• /
• pp.31-40
• /
• 2023

We installed temporary strong motion seismometers at the ground surface, 1 m, 2 m, and 9 m at an existing seismic station that houses permanent seismometers installed at 20 m and 100 m, to investigate the influence of installation depth on the recorded ambient and anthropogenic noise level and the characteristics of earthquake signals. Analysis of the ambient noise shows that anthropogenic noise dominates where vibration period T < 1 s at the studied site, whereas wind speed appears to be strongly correlated with the noise level at T > 1 s. Frequency-wavenumber analysis of 2D seismometer array suggests that ambient noise in short periods are predominantly body waves, rather than surface waves. The level of ambient noise was low at 9 m and 20 m, but strong amplification of noise level at T < 0.1 s was observed at the shallow seismometers. Both the active-source test result and the recorded earthquake data demonstrated that the signal level is decreased with the increase of depth. Our result also shows that recorded motions at the ground and 1 m are strongly amplified at 20 Hz (T = 0.05 s), likely due to the resonance of the 3 m thick soil layer. This study demonstrates that analysis of ambient and active-source vibration may help find optimal installation depth of strong motion seismometers. We expect that further research considering various noise environments and geological conditions will be helpful in establishing a guideline for optimal installation of strong motion seismometers.

• Smart Structures and Systems
• /
• v.12 no.6
• /
• pp.679-694
• /
• 2013

In this paper the application of the Interpolation Damage Detection Method to the numerical model of a suspension bridge instrumented with a network of Micro-Electro-Mechanical System sensors is presented. The method, which, in its present formulation, belongs to Level II damage identification method, can identify the presence and the location of damage from responses recorded on the structure before and after a seismic damaging event. The application of the method does not require knowledge of the modal properties of the structure nor a numerical model of it. Emphasis is placed herein on the influence of recorded signals noise on the reliability of the results given by the Interpolation Damage Detection Method. The response of a suspension bridge to seismic excitation is computed from a numerical model and artificially corrupted with random noise characteristic of two families of Micro-Electro-Mechanical System accelerometers. The reliability of the results is checked for different damage scenarios.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2007.06a
• /
• pp.163-166
• /
• 2007

KMA established short period seismometer, accelerometer, and ocean bottom seismometer network to build the detail earthquake monitoring system and Tsunami monitoring system. KMA also replaced borehole seismometer and wave height meter monitoring system. The purposes of this study are to record the ambient seismic noise levels of short period seismometer and accelerometer installed in 2006 and 2007, and compare their characteristics to present the standard of site selection criteria.