• Journal of the Korean earth science society
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• v.30 no.7
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• pp.824-833
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• 2009

We analyzed a total of six months of geomagnetic data obtained at Cheonyang observatory, which is operated by Korean Meteorological Administration, to monitor earthquake precursors. Geomagnetic transfer functions (GTFs) and polarization values, which reflect the time-variations of the resistivity of subsurface, were estimated from 3-component geomagnetic data. The time-variant fluctuations were compared with the earthquake events occurred in the same period. Now that the daily GTFs show fairly irregular variations, we can not identify any correlation with the already occurred earthquakes and Kp index. On the other hand, we detect clear increases of the Ultra-Low-Frequency (ULF) band polarization values before the earthquakes, but the similar features are also observed even though the earthquake did not occur. This result may indicate that these time-variations are not just due to the earthquake precursor. For further understanding about these results, we need to investigate the relationship between the previous earthquake events and the geomagnetic data of other observatories.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.383-383
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• 2022

기존 큰 지진을 대상으로 한 많은 연구결과들을 살펴보면, 큰 지진이 발생하기 전에 토양 속에 존재하는 다양한 인자들 중에 라돈(²²²Rn, 반감기=3.82일) 농도가 비정상적으로 증가하는 현상을 나타낸다. 이러한 결과들은 라돈발생의 경향성을 분석한다면, 지진발생에 대한 전조증상이나 예측이 가능함을 나타낸다. 본 연구에서는 포항지역을 중심으로 지진발생에 대한 전조증상이나 모니터링을 분석하기 위해 지하수 관측소에 설치된 라돈 관측기기에서 라돈 관측자료를 수집하고 이를 활용하는 연구를 수행하였다. 라돈 관측자료 기간은 2019년 11월부터 2020년 9월까지의 자료이며, 라돈인자 뿐만 아니라 지하수위, 강수량, 수온인자를 같이 분석하였으며, 동일기간 동안 발생한 진도 2 이상의 지진사례 6개(E1(M_L 3.5): 2019.12.30.; E2(M_L 3.2): 2020.01.30.; E3(M_L 2.4): 2020.02.09.; E4(M_L 2.7): 2020.02.16.; E5(M_L 2.8): 2020.05.27.; E6(M_L 2.1): 2020.09.22.)를 대상으로 하였다. 지진발생의 전조증상이 나타나는 지역을 분석하기 위해 Dobrovolsky radius values (Dobrovolsky et al., 1979)와 Harversine 관계식을 적용하였다. 적용결과, 시간적 분석에서 라돈의 증감 경향성이 지진발생의 전조증상과 유의미한 상관성이 있음을 확인하였으며, 공간적인 분석에서도 유의미하지는 않으나 상관성이 나타났다. 그 외 지하수위는 상관성이 어느 정도 나타났으나 강수량은 유의미한 결과를 나타내지는 않았다. 따라서 라돈을 활용한다면 지진발생의 전조증상을 시공간적으로 파악할 수 있음을 확인하였다.

• Journal of the Korean earth science society
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• v.30 no.6
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• pp.683-691
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• 2009

Geomagnetic variation around May 2, 2009 when Angdong earthquake broke out was analyzed using the data recorded at the Cheong-yang geomagnetic observatory, KMA. Firstly, we predict the geomagnetic variation by PCA analysis of geomagnetic data, and then compare the predicted value with the observed data to find any significant differences in residuals. Secondly, wavelet semblance technique is applied to compare the time series before and after the earthquake. Some meaningful change is detected in the Z-field. Thirdly, eigen value analysis for the 3 component geomagnetic data is performed. The location of the observatory was too far from the epicenter and the magnitude was too small to find decisive precursory phenomenon. Nevertheless we can detect some significant correlation between the earthquake and the variation of the geomagnetic field. Various signal processing methods applied in this study will give some opportunity to find precursory effects in the future.

• Economic and Environmental Geology
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• v.51 no.4
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• pp.393-400
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• 2018

Despite some skeptical views on the possibility of earthquake prediction, observation and evaluation of precursory changes have been continued throughout the world. In Korea, the public concern on the earthquake prediction has been increased after 2016 $M_L5.8$ and 2017 $M_L5.4$ earthquakes occurred in Gyeongju and Pohang, the southeastern part in Korea, respectively. In this study, the abnormal increase of groundwater level was observed before the 2016 $M_L5.8$ Gyeongju earthquake in a borehole located in 52 km away from the epicenter. The well was installed in the Yangsan fault zone, and equipped for the earthquake surveillance. The abnormal change in the well would seem to be a precursor, considering the hydrogeological condition and the observations from previous studies. It is necessary to set up a specialized council to support and evaluate the earthquake prediction and related researches for the preparation of future earthquake hazards.

• Journal of the Society of Disaster Information
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• v.13 no.1
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• pp.89-95
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• 2017

The cases of animals unusual behavior have been reported occasionally before a major disaster occurs. Could animals unusual behavior associated with a major disaster occurrence, if so, could we foreknow a disaster occurrence? The purpose of study is to quest an answer through literature reviews on the relation between animals unusual behavior and premonitory symptoms of an earthquake. These empirical studies are classified three parts according as methodological framework; statistical analysis, experimental analysis, observation analysis. The results are simply divided as two, 'animals unusual behavior may be seen as a precursor of pre-disaster phenomena' and 'difficult to see.' A number of studies have been performed abroad, however there is no one in Korea. Most of the studies point out common limitations-difficult to verify the reliability of data, accidentally get and fewer samples of data, difficulty of ensuring appropriate data, etc. That is why more related research with animals unusual behavior and disaster occurrence is needed to validate cause-and-effect relation of animal unusual behavior and pre-disaster phenomena.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.249-255
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• 2010

Since the 1990's, a number of ULF geomagnetic disturbance associated with earthquake occurrences have actively been reported, and polarization analysis of geomagnetic fields becomes one of potential candidates to be capable of predicting short-term earthquake. This study develops the modified polarization analysis method based on the previous studies, and analyzes three-component geomagnetic fields obtained at Cheongyang geomagnetic observatory using the developed method. A daily polarization value (the ratio of spectral power of horizontal and vertical geomagnetic field) is calculated with a focus on the 0.01 Hz band, which is known to be the most sensitive to seismogenic ULF radiation. We analyze a total of 10 months of geomagnetic data obtained at Cheongyang observatory, and compare the polarization values with the Kp index and the earthquake occurred in the analysis period. The results show that there is little correlation between the temporal variations of polarization values and Kp index, but remarkable increases in polarization values are identified which are associated with two earthquakes. Comparison the polarization values obtained at Cheongyang and Kanoya observatory indicates that the increases of polarization values at Cheongyang might be due to not global geomagnetic induction but the locally occurred earthquakes. Furthermore, these features are clearly shown in normalized polarization values, which take account in the statistical characteristics of each geomagnetic field. On the basis of these results, polarization analysis can be used as promising tool for monitoring the earthquake-precursory phenomenon.

• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.228-235
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• 2016

We investigated pre- and post- seismic total electron content (TEC) anomalies in ionosphere caused by recent large-scale earthquakes around the globe and additionally examined whether the similar phenomena are detected in connection with the earthquakes around the Korean Penisula. TEC anomalies associated with the large-scale earthquakes showed the similar results to previous studies. In addition, we newly found the similar TEC changes from the recent 2016 Ecuador earthquake (M7.8). However, the post-seismic TEC changes would be falsely interpreted as the pre-seismic TEC changes dependent on the post-processing of TEC observation. We also investigated the possibility of TEC responses from the recent domestic earthquakes including 2016 Gyeongju earthquake but could not find any anomalous TEC changes. This is probably because the domestic earthquakes release significantly smaller acoustic wave energy than that of large-scale earthquakes occurring in plate boundaries.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.21-33
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• 2015

This study tests the potential of detecting small-magnitude earthquakes (~M3.0) and their precursors using a long-term groundwater-monitoring database. In groundwater records from April to June 2012, abnormal changes in water level, temperature, and electrical conductivity were identified in the bedrock monitoring wells of the Gimcheon-Jijwa, Gangjin-Seongjeon, and Gongju-Jeongan stations. These anomalies could be attributed to the M3.1 earthquake that occurred in the Youngdeok area on May 30th, although no linear relationship was found between the scale of changes and the distance between each monitoring station and the epicenter, which is attributed in part to the wide screen design of the monitoring wells. Groundwater monitoring networks designed specifically for monitoring earthquake impacts could provide better information on the safety of underground space and on the security of emergency water-resources in earthquake disaster areas.

• Geophysics and Geophysical Exploration
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• v.19 no.2
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• pp.91-96
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• 2016

From the Earth's polar motion time series (IERS 08 C04, since 1981), after removal of seasonal variation by band-pass filtering, we acquired Earth's free Eulerian motion (Chandler wobble) time series. By successive least square error fittings on it, we analyzed amplitude and phase variation of Chandler wobble. We attempted to identify any precursory behavior of the pole before large earthquakes but only to fail. Unlike Smylie's conjecture there was no appreciable motion of the Earth's pole detected at around the each times of recent six largest earthquakes of magnitude over 8.5.

• Tunnel and Underground Space
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• v.18 no.1
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• pp.1-9
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• 2008

Acoustic emission (AE) and Microseimsic (MS) activities are law-energy seismic events associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. The main difference between AE and MS signals is that the seismic motion frequencies of AE signals are higher than those of MS signals. As the failure of geotechnical structures usually happens as a high velocity and small displacement, it is nat easy ta determine the precursor and initiation stress level of failure in displacement detection method. To overcame this problem, AE/MS techniques far detection of structure failure and damage have recently adapt in civil engineering. This study deal with the basic theory of AE/MS and state of arts in monitoring technique using AE/MS.