• Title/Summary/Keyword: Seismic Blind Zone

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Application of the Onsite Earthquake Early Warning Technology Using the Seismic P-Wave in Korea (P파를 이용한 지진 현장 경보체계기술의 국내 적용)

  • Lee, Ho-Jun;Lee, Jin-Koo;Jeon, Inchan
    • Journal of the Society of Disaster Information
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    • v.14 no.4
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    • pp.440-449
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    • 2018
  • Purpose: This study aims to design and verify an onsite EEWS that extracts the P-wave from a single seismic station and deduce the PGV. Method: The P-wave properties of Pd, Pv, and Pa were calculated by using 12 seismic waveform data extracted from historic seismic records in Korea, and the PGVs were computed using empirical equation on the P properties - PGV relationship and compared with the observed values. Results: Comparison of the observed and estimated PGVs within the alarm level shows the error rate of 86.7% as minimum. By reducing the PTW to 2 seconds, the alarm time can be shortened by 1 second and the seismic blind zone near the epicenter can be shortened by 6 Km. Conclusion: Through this study, we confirmed the availability of the on-site EEWS in Korea. For practical use, it is necessary to develop regression formula and algorithm reflect local effect in Korea by increasing the number of seismic waveform data through continuous observation, and to eliminate the noise from the site.

A Field Application of 3D Seismic Traveltime Tomography (I) - Constitution of 3D Seismic Traveltime Tomography Algorithm - (3차원 탄성파 토모그래피의 현장 적용 (1) - 3차원 토모그래피 알고리즘의 구성 -)

  • Moon, Yoon-Sup;Ha, Hee-Sang;Ko, Kwang-Buem;Kim, Ji-Soo
    • Tunnel and Underground Space
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    • v.18 no.3
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    • pp.202-213
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    • 2008
  • In this study, theoretical approach of 3D seismic traveltime tomography was investigated. To guarantee the successful field application of 3D tomography, appropriate control of problem associated with blind zone is pre-requisite. To overcome the velocity distortion of the reconstructed tomogram due to insufficient source-receiver array coverage, the algorithm of 3D seismic traveltime tomography based on the Fresnel volume was developed as a technique of ray-path broadening. For the successful reconstruction of velocity cube, 3D traveltime algorithm was explored and employed on the basis of 2nd order Fast Marching Method(FMM), resulting in improvement of precision and accuracy. To prove the validity and field application of this algorithm, two numerical experiments were performed for globular and layered models. The algorithm was also found to be successfully applicable to field data.

Advanced and Application of Onsite EEW Technology in Korea (국내에서의 지진현장경보 기술 고도화 및 적용)

  • Lee, Ho Jun;Jeon, Inchan;Seo, Jeong Beom;Lee, Jin Koo
    • Journal of the Society of Disaster Information
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    • v.16 no.4
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    • pp.670-681
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    • 2020
  • Purpose: This study aims to derive a PGV prediction equation and to enhance the application of the Onsite EEW technology which has developed through previous studies. Method: The prediction equation for the Onsite EEW derived from earthquake data M≥3.0 and MMI≥II over the past four years. Local seismic risk is estimated using M and PGV deduced from P wave properties. Result: The improved PGV prediction equation estimated the MMI with an average accuracy of 94.8% and the 𝜏c : Pd method also showed valid performance for alerting local seismic risks. Conclusion: Onsite EEW technology is successfully applied to Korea, and becomes to reduce the blind zone to about 14km.

A Study to Determine the Degree of Difficulties with the Excavation of Corestone Weathering Profiles (핵석지반에서의 굴착난이도 평가방법 연구)

  • Lee, Su-Gon;Lee, Byok-Kyu;Kim, Min-Sung
    • The Journal of Engineering Geology
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    • v.17 no.1 s.50
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    • pp.89-99
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    • 2007
  • This paper intends to introduce more objective and qualitative rock mass classification method easily applicable to the excavation of gneissic masses showing corestone weathering profiles. It is proven that corestone weathering profile could be divided with reasonable accuracy into digging, ripping and blasting layers using visual and simple mechanical techniques such as Schmidt hammer rebound test on cut slopes, taking into consideration strength and spacial distribution of corestone, workability and work efficiency of excavation. Also, seismic refraction surveys were employed for shallow investigations (down to $20{\sim}30m$ depth) in corestone weathering profile and conducted across the top of vertical exposures where the underlying geology could be directly inspected. Some discrepancies ($3{\sim}4m$ in average and 6 m occasionally) between the actual and assumed materials with respect to seismic velocities were observed. Thus it can be concluded that field geotechnical mapping and field seismic test should be used together in order to get a relatively good accuracy in assessing likely excavation conditions of corestone weather-ing profiles.