지구물리와물리탐사 (Geophysics and Geophysical Exploration)

  • 제22권1호
  • /
  • Pages.21-28
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  • 2019
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  • 1229-1064(pISSN)
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  • 2384-051X(eISSN)
한국지구물리·물리탐사학회 (Korean Society of Earth and Exploration Geophysicists)
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표면파 토모그래피를 이용한 사우디아라비아의 S파 속도구조 및 이방성 연구

S-wave Velocity Structure and Radial Anisotropy of Saudi Arabia from Surface Wave Tomography

  • 김린희 (강원대학교 지질.지구물리학부) ;
  • 장성준 (강원대학교 지질.지구물리학부) ;
  • ;
  • Kim, Rinhui (Division of Geology and Geophysics, Kangwon National University) ;
  • Chang, Sung-Joon (Division of Geology and Geophysics, Kangwon National University) ;
  • Mai, Martin (King Abdullah University of Science and Technology (KAUST)) ;
  • Zahran, Hani (Saudi Geological Survey (SGS))
  • 투고 : 2019.01.11
  • 심사 : 2019.02.27
  • 발행 : 2019.02.28
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초록

이 연구에서는 사우디 아라비아 지역의 S파 속도구조와 이방성을 알아보기 위해 표면파 분산 곡선을 사용하여 3차원 토모그래피를 수행하였다. 아라비아 반도는 지질학적 및 지형적으로 순상지(shield)와 플랫폼(platform)의 지형으로 나뉜다. 본 연구에서는 사우디 지질조사소(Saudi Geological Survey)에서 받은 2008 ~ 2014년 기간의 규모 5.5 이상, 진앙거리 $40^{\circ}$ 이내인 지진 자료들을 사용하였다. 획득한 자료들은 전처리를 거쳐 다중 필터 기법(multiple filter technique)을 적용하여 분산 곡선을 구하였다. 주기 5 ~ 140초에 해당하는 러브파와 레일리파의 군속도 분산 곡선을 역산하여 10 ~ 60 km에서의 SH파와 SV파 속도모델 그리고 이방성을 계산하였다. 그 결과 SV파의 속도모델에서는 순상지 하부 10 ~ 30 km 깊이에서 고속도 이상대를 보이며, 플랫폼 하부에서는 10 km 깊이에서 저속도 이상대를 보인다. 이는 순상지가 원생누대 기원의 오래되고 차가운 육괴로 되어있으며, 플랫폼이 고생대, 중생대, 신생대의 퇴적물로 덮여 있기 때문에 이와 같은 결과가 나왔다고 판단된다. SV파와 SH파의 속도 차이를 이용하여 구한 이방성의 결과는 전반적으로 양의 이방성이 나타나며, 이는 자그로스 조산대에서의 섭입으로 인한 아라비아 판의 당김에 의해 인장력이 수평 방향으로 발생하여 SH파의 속도가 빠르게 나타난다고 판단된다.

We perform a 3D tomographic inversion using surface wave dispersion curves to obtain S-velocity model and radial anisotropy beneath Saudi Arabia. The Arabian Peninsula is geologically and topographically divided into a shield and a platform. We used event data with magnitudes larger than 5.5 and epicentral distances shorter than $40^{\circ}$ during 2008 ~ 2014 from the Saudi Geological Survey. We obtained dispersion curves by using the multiple filtering technique after preprocessing the event data. We constructed SH- and SV-velocity models and consequently radial anisotropy model at 10 ~ 60 km depths by inverting Love and Rayleigh group velocity dispersion curves with period ranges of 5 ~ 140 s, respectively. We observe high-velocity anomalies beneath the Arabian shield at 10 ~ 30 km depths and low-velocity anomalies beneath the Arabian platform at 10 km depth in the SV-velocity model. This discrepancy may be caused by the difference between the Arabian shield and the Arabian platform, that is, the Arabian shield was formed in Proterozoic thereby old and cold, while the Arabian platform is covered by predominant Paleozoic, Mesozoic, and Cenozoic sedimentary layers. Also we obtained radial anisotropy by estimating the differences between SH- and SV-velocity models. Positive anisotropy is observed, which may be generated by lateral tension due to the slab pull of subducting slabs along the Zagros belt.

키워드

MRTSBC_2019_v22n1_21_f0001.png 이미지

Fig. 2. Ray paths between epicenters and stations for (a) Rayleigh waves and (b) Love waves. Red circles and blue triangles indicate the locations of epicenters and stations, respectively.

MRTSBC_2019_v22n1_21_f0002.png 이미지

Fig. 3. Group velocity dispersion curves for (a) Rayleigh waves and (b) Love waves with a period range from 5 to 140 s.

MRTSBC_2019_v22n1_21_f0003.png 이미지

Fig. 4. The depth slices of SV-wave velocity perturbations from checkerboard tests. The input checkerboard models consist of 400 km × 400 km squared anomalies with amplitudes of ± 300 m/s as shown in (a). The other panels show inversion results at (b) 10, (c) 20, (d) 30, (e) 40, (f) 50 and (g) 60 km. Regions not covered by data sets are indicated in gray.

MRTSBC_2019_v22n1_21_f0004.png 이미지

Fig. 5. The depth slices of SH-wave velocity perturbations from checkerboard tests. The input checkerboard models consist of 400 km × 400 km squared anomalies with amplitudes of ± 300 m/s as shown in (a). The other panels show inversion results at (b) 10, (c) 20, (d) 30, (e) 40, (f) 50 and (g) 60 km. Regions not covered by data sets are indicated in gray.

MRTSBC_2019_v22n1_21_f0005.png 이미지

Fig. 6. The depth slices of SV-wave velocity model at (a) 10, (b) 20, (c) 30, (d) 40, (e) 50 and (f) 60 km. Regions not covered by data sets are indicated in gray.

MRTSBC_2019_v22n1_21_f0006.png 이미지

Fig. 7. The depth slices of SH-wave velocity model at (a) 10, (b)20, (c) 30, (d) 40, (e) 50 and (f) 60 km. Regions not covered by data sets are indicated in gray.

MRTSBC_2019_v22n1_21_f0007.png 이미지

Fig. 8. Radial anisotropy at (a) 10, (b) 20, (c) 30, (d) 40, (e) 50 and (f) 60 km. Most of the Arabian Peninsula is dominated by positive anisotropy. Regions not covered by data sets are in dicatedin gray.

MRTSBC_2019_v22n1_21_f0008.png 이미지

Fig. 1. (a) Map of the study area. The red lines indicate plate boundaries and the dashed line represents the boundary between the Arabian shield and the Arabian platform. The black arrows indicate the direction of absolute plate motions (ArRajehi et al., 2010). Stations, volcanoes and volcanic field are indicated by blue squares, red triangles and orange areas, respectively. (b) Distribution of events. The blue triangle is the center point of our model and red circles indicate events.

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