ULF Electromagnetic Variation Associated with Seismic Wave

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2005 Vol.42, Issue 6 Preview Page Next Page

ULF Electromagnetic Variation Associated with Seismic Wave 지진파에 의해 발생하는 ULF 대역 전자기장 변동: 이춘기, 이희순, 권병두, 양준모, 오석훈, 송윤호, 이태종, Toshihiro Uchida
Choon-Ki Lee, Heuisoon Lee, Byung-Doo Kwon, Jun-Mo Yang, Seokhoon Oh, Yoonho Song, Tae Jong Lee and Toshihiro Uchida

31 December 2005. pp. 603-611

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Abstract

The ULF electromagnetic signals associated with the seismic activity in the south-east offshore of Kii peninsula, Japan, were clearly recorded at the MT sites in Jeju island, Korea. In this research, we have identified the co-seismic electromagnetic signals associated with the seismic activity and have analyzed the characteristics of significant electromagnetic variations. The analysis of power spectral density shows that the significant earthquake signals have the frequency band of about 0.05 to 0.5 Hz. During the earthquake, the apparent resistivity increases and phase converges on zero-phase. The phase velocity of EM wave is about 3.4-4.5 km/s and is similar to the velocity of S or Surface wave. This means the EM signals are induced by the passage of seismic wave. The differences of amplitudes and directions of EM wave at two MT sites may mean that the co-seismic responses are locally affected by the geoelectric or hydrogeologic structures.

Keywords

Co-seismic EM

signal

Magnetotellurics

Seismic wave

최근 제주도에서 실시된 자기지전류(magnetotelluric, MT) 탐사 자료에서 일본의 Kii 반도 남동쪽 해상에서 발생한 지진활동과 관련된 ULF 대역의 전자기 현상이 관측되었으며, 이 전자기장 신호의 특성을 분석하였다. 파워 스펙트럼 분석으로부터 주된 에너지가 0.5-0.05 Hz에 집중되어 있음을 알 수 있으며 지진관련 신호가 포함된 경우 MT 임피던스의 겉보기 비저항은 증가하고 위상은 0°에 가까워진다. 위상 속도는 S파 혹은 표면파에 가까우므로 전자기장 변동이 지진파의 전파에 의해 유도된 것임을 의미한다. 동-서 측점에서 전자기 신호의 크기와 타원분극 방향이 큰 차이를 보이는 것은 지진파 전파에 의해 유도되는 전자기장 변동이 측점 주변의 국지적인 지전기 및 수리지질학적 구조에 의해 영향을 받은 것으로 해석된다.

키워드

동지진 전자기 신호

자기지전류 탐사

지진파

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