Geophysics and Geophysical Exploration (지구물리와물리탐사)

Korean Society of Earth and Exploration Geophysicists (한국지구물리·물리탐사학회)
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P-wave Velocity Anisotropy in the Upper Crust of the Southern Korean Peninsula Using Seismic Signals from Large Explosions

대규모 발파자료를 이용한 한반도 남부 상부지각의 종파 속도 이방성

  • Hong, Myung-Ho (Department of Geophysics, Kangwon National University) ;
  • Kim, Ki-Young (Department of Geophysics, Kangwon National University)
  • 홍명호 (강원대학교 지구물리학과) ;
  • 김기영 (강원대학교 지구물리학과)
  • Published : 2009.08.31
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Abstract

As part of seismic experiments investigating crustal velocity structures of the Korean peninsula, permanent (fixed) seismographs of the Korea Meteorological Administration (KMA) network recorded seismic signals from four and eight large explosions in Korean Crustal Research Team (KCRT) profiles shot in 2004 and 2008, respectively. Among the seismograms recorded by 43 velocity sensors and 103 accelerometers at KMA stations distributed throughout the southern Korean Peninsula, 156 records with epicentral distances less than 120 km and high signal-to-noise ratios were analyzed to determine velocity anisotropy of the Pg phase. Relative elevation corrections of -101.6 to 105.3 ms were made using velocity information derived from the 2004 KCRT profile data and differences in elevation between the permanent KMA stations and the temporary stations in the KCRT profiles at the same source-receiver offsets. To remove site effects, receiver-station corrections of -89.6 to 192.2 ms were additionally made to the KMA station data by subtracting the average differences in traveltimes between KMA stations and portable stations at the same offsets for all available shots with different azimuths. With the exception of anomalously fast velocities along trends of the Chugaryeong fault zone and the Okchon fold belt and anomalously slow velocities in the regions of high terrestrial heat near Yeongduk and Ulsan, the analysis of crustal velocity anisotropy using the Pg phase indicates overall isotropy in the southern half of the Korean peninsula.

한반도 지각속도 구조 규명을 위해 실시하고 있는 지각규모 탄성파 실험의 일환으로 한반도 지각구조 연구팀이 2004년도와 2008년도에 조사측선상의 각 4개소와 8개소에서 인공적으로 대규모 지진파 신호를 발생시켰으며, 이 지진파 신호들이 기상청 지진망의 고정관측소 지진계에 기록되었다. 43개 속도센서와 103개 가속도센서로 기록된 고정관측소 자료 중, 신호/잡음비가 양호한 진앙거리 120 km 이내의 156개 자료만을 대상으로 Pg 위상의 속도 이방성을 분석하였다. 상대고도보정은 KCRT-2004 자료분석을 통해 구한 지표부근 속도정보와 고정관측소와 측선상의 이동식 관측소 사이의 고도차이를 이용하여 구하였으며, -101.6 ${\sim}$ 105.3 ms의 범위를 갖는다. 부지효과를 제거하기 위한 관측소 잔여보정은 가용한 모든 방향의 발파자료를 대상으로, 고정관측소 주시와 이동관측소 주시의 차이를 발파점별로 평균한 값을 제거하는 방법으로 구하였으며, -89.6 ${\sim}$ 192.2 ms 범위를 갖는다. 추가령 지구대와 옥천계 구조선 방향으로 나타나는 빠른 속도 이상대와 영덕과 울산 부근 높은 지열대의 느린 속도 이상대를 제외하면, Pg 위상으로 구한 한반도 남부의 상부지각속도는 전반적으로 등방성임을 지시한다.

Keywords

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