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Kafe 바로가기주관연구기관 | 연세대학교 Yonsei University |
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보고서유형 | 최종보고서 |
발행국가 | 대한민국 |
언어 | 한국어 |
발행년월 | 2015-02 |
과제시작연도 | 2014 |
주관부처 | 기상청 Korea Meteorological Administration(KMA) |
등록번호 | TRKO201500013502 |
과제고유번호 | 1365001923 |
사업명 | 지진기술개발사업 |
DB 구축일자 | 2015-08-15 |
키워드 | 한반도.지진원 특성.지각구조 특성.지구조.지진 분포.Korean Peninsula.seismic source.crustal structure.tectonics.seismicity. |
DOI | https://doi.org/10.23000/TRKO201500013502 |
한반도에는 규모 5이상의 지진이 1978년 이후로 5회 발생했고, 역사기록물에 따르면 한반도에는 많은 중대형 지진이 발생했음을 확인할 수 있다. 인구가 밀집한 한반도의 경우, 이러한 중대형 지진으로 큰 피해를 입을 수 있다. 본 연구는 한반도 주위에서 발생하는 지진의 계기 및 역사 지진을 바탕으로 지진 분포의 특성을 분석하고, 지진 발생에 따른 지진동의 특성을 규명한다. 경로별 지진파의 감쇄와 증폭 현상을 이해하며, 그 변화를 정량적으로 측정한다. 이를 위해 한반도 및 주변 지역의 지각구조와 속도 구조의 특성 이해를 동반한다. 한반
한반도에는 규모 5이상의 지진이 1978년 이후로 5회 발생했고, 역사기록물에 따르면 한반도에는 많은 중대형 지진이 발생했음을 확인할 수 있다. 인구가 밀집한 한반도의 경우, 이러한 중대형 지진으로 큰 피해를 입을 수 있다. 본 연구는 한반도 주위에서 발생하는 지진의 계기 및 역사 지진을 바탕으로 지진 분포의 특성을 분석하고, 지진 발생에 따른 지진동의 특성을 규명한다. 경로별 지진파의 감쇄와 증폭 현상을 이해하며, 그 변화를 정량적으로 측정한다. 이를 위해 한반도 및 주변 지역의 지각구조와 속도 구조의 특성 이해를 동반한다. 한반도 인근 지역에서 발생한 다양한 지진을 분석하였으며, 국지 지진 및 지역지진파형 분석을 수행하였다. 본 연구에서는 한반도에서 관측된 지진파형 자료 뿐 아니라, 일본 열도에서 관측된 자료를 수집하였다. 특별히 2013년도 서해 지역 연쇄 지진 분석을 위하여 연속 파형 자료등을 수집하여, 연구를 성공적으로 수행하였다. 본 연구에서는 파형 역산과 위상분석 방법등을 활용하여, 단층면해을 결정하였다. 여러 다양한 경로에서 지진파형 자료를 분석하였으며, 그 위상의 진폭과 감쇠 특성을 분석하였다. 한반도의 급격한 지각구조 변화에 따른 지진파 특성 변화 연구를 통해 잠재 지진 위험성을 평가하였다. 다양한 지각경로에 대해 지진파 감쇠 및 증폭 분석을 수행하였으며, 지진 규모의 정확한 산정을 위해 필요한 보정 방식연구와 지각구조 특성 연구를 수행하였다. 또한 고지구조 연관 구조에서 발생하는 다양한 지진파 특성을 분석하였으며, 한반도 지진 특성을 성공적으로 분석하였다.
II. Research and results
Regional seismic analysis is an only way to investigate the source properties of small or moderate-sized seismic events that occur in physically unaccessible regions such as oceanic regions and politically-prohibited regions. The ground motions by earthquakes need to be u
II. Research and results
Regional seismic analysis is an only way to investigate the source properties of small or moderate-sized seismic events that occur in physically unaccessible regions such as oceanic regions and politically-prohibited regions. The ground motions by earthquakes need to be understood for better mitigation of seismic hazards particularly in continentalmargins that often incorporate high seismicity. It has not been fully understood howseismicwaves interact with complex crustal structures in continental margins. Responses of regional waves to complex crustal structures need to be quantified. Analysis of regional waveforms from controlled sources is desirable for investigation of influence of crustal structures. The influence of continental margin around the Korean Peninsula is investigated in terms of spectral contents, horizontal-to-vertical (H/V) spectral ratios and quality factors using regional waveforms for the 2009 North Korean underground nuclear explosion test that was well recorded by stations in the southern Korean Peninsula. Regional waveforms and spectral amplitudes vary significantly by path. Spectral contents of regional phases are different among stations in common great-circle directions. All regional phases modulate highly in continental margins. Path-dependent seismic attenuation is strong in low frequencies (≤3 Hz), and weak in high frequencies (N3 Hz). Continental margins cause directional energy partition of regional waves depending on the path. Regional waves attenuate highly in passage across continental margin, and then regrowon continental paths. The growth rate is stronger than inherent attenuation rate, causing seismic amplification. The shapes of H/V ratios are similar among various regional phases at common stations. On the other hand, the H/V ratios for common phases vary by station in the same azimuths. Characteristic differences in H/V ratios between two horizontal components suggest directional partition of seismic energy by crustal structures in the paths.
The Japanese Islands were separated from the Eurasian plate due to continental rifting during the Oligocene to mid-Miocene, which caused the opening of the East Sea (Sea of Japan). Such tectonic evolution in the East Sea is important for understanding the evolution of back-arc regions with active convergent margins. To understand the evolution of the paleo-rifted back-arc region,we investigate seismicity, crustal seismic anisotropy, focal mechanism solutions and ambient stress field around the Korean Peninsula. The Korean Peninsula displays diffused seismicitywith small andmoderate earthquakes. Shallowearthquakes rarely occur in the central East Sea. The crustal fast shear-wave polarization directions in the Korean Peninsula are observed to vary in azimuth between 40° and 90°. The focalmechanismsolutions are calculated by long periodwaveform inversions. The ambient stress field is calculated fromthe focalmechanismsolutions. The compressional stress field in the Korean Peninsula is observed to be in ENE-WSW,which is consistent with the fast shear-wave polarization directions. The compressional stress directions in the East Sea progressively change from ENE to SE with increasing longitude. The rapid change of compressional directions in the central East Sea prohibits accumulation of stress, causing rare shallow seismicity. High seismicity of reverse faulting events is observed at the fringes of the East Sea, in particular, around the east coast of the Korean Peninsula and the west coast of Japanese Islands, which correspond to paleo-rifted margins where compressional stresses are accumulated. The compressional stress field and active thrustal events suggest reverse activation of paleo-normal faults that were developed during the opening of the East Sea.
The Korean Peninsula, eastern China and the Yellow Sea comprise the eastern Eurasian plate, and are believed to share considerable tectonic evolution history. The tectonic structures in the Yellow Sea are poorly understood, raising difficulty in reconstruction of tectonic evolution history in the eastern Eurasian plate. The tectonic structures in the Yellow Sea are constrained by seismicity and fault-plane solutions of earthquakes. The fault-plane solutions are determined by waveform inversions and seismic phase polarity analyses. The ambient stress fields are deduced from the fault-plane solutions. The primary stress field around the Yellow Sea is composed of ENE– WSW directional compression and NNW– SSE directional tension. Normal-faulting earthquakes with ENE– WSW directional strikes are observed in the central Yellow Sea between the Shandong Peninsula and the central Korean Peninsula. The normal-faulting region is interpreted to be a northern margin of collision belt between the North and South China blocks. The normal-faulting system suggests post-collisional lithospheric delamination, causing reverse activation of paleo-thrustal faults that were developed by the collision between the North and South China blocks in the early Jurassic period.
The P and S velocity ratio, Vp/Vs, is a seismic property that is convertible to Poisson’s ratio, a widelyanalyzed physical property of elastic materials. The lateral variation in the Vp/Vs ratios of the upper crust of the southern Korean Peninsula is investigated based on the travel times of P and S waves of local events with epicentral distances of 50 km or less and focal depths of 25 km or less. The dense seismic networks in the Korean Peninsula allow us to investigate the regional variation of VP/VS ratios. These Vp/Vs ratios are estimated to be 1.60– 1.91 with an average of 1.69. The VP/VS ratios are as high as 1.73– 1.91 in the Gyeongsang basin, Jeju island and offshore region of the eastern Okcheon belt, but have relatively low values of 1.64– 1.72 in Precambrian massif regions. The stability of the Vp/Vs ratios is tested with randomly-resampled travel-time data, the results of which suggest nearly constant Vp/Vs ratios with increasing depth in the upper crust. The influences of plausible errors on origin times and arrival times are quantified to verify the Vp/Vs estimates. The Vp/Vs ratios are correlated with geological and tectonic structures. Comparisons with known seismic and geophysical properties suggest that structural features observed on the surface may extend at least to the mantle lid.
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