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Econ. Environ. Geol. 2023; 56(4): 365-384

Published online August 30, 2023

https://doi.org/10.9719/EEG.2023.56.4.365

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

S-velocity and Radial Anisotropy Structures in the Western Pacific Using Partitioned Waveform Inversion

Ji-hoon Park1, Sung-Joon Chang1,*, Michael Witek2

Author Info. +

1Department of Geophysics, Kangwon National University, Chuncheon, South Korea
2Los Alamos National Lab, New Mexico, USA

Correspondence to : *sjchang@kangwon.ac.kr

Received: June 5, 2023; Revised: July 27, 2023; Accepted: August 7, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

We applied the partitioned waveform inversion to 2,026 event data recorded at 173 seismic stations from the Incorporated Research Institutions for Seismology Data Managing Center and the Ocean Hemisphere network Project to estimate S-wave velocity and radial anisotropy models beneath the Western Pacific. In the Philippine Sea plate, high-Vs anomalies reach deeper in the West Philippine basin than in the Parece-Vela basin. Low-Vs anomalies found at 80 km below the Parece-Vela basin extend deeper into the West Philippine Basin. This velocity contrast between the basins may be caused by differences in lithospheric age. Low-Vs anomalies are observed beneath the Caroline seamount chain and the Caroline plate. Overall positive radial anisotropy anomalies are observed in the Western Pacific, but negative radial anisotropy is found at > 220 km depth on the subducting plate along the Mariana trench and at ~50 km in the Parece-Vela basin. Positive radial anisotropy is found at > 200 km depth beneath the Caroline seamount chain, which may indicate the 'drag' between the plume and the moving Pacific plate. High-Vs anomalies are found at 40 ~ 180 km depth beneath the Ontong-Java plateau, which may indicate the presence of unusually thick lithosphere due to underplating of dehydrated plume material.

Keywords partitioned waveform inversion, radial anisotropy, Western Pacific, Philippine Sea plate, Caroline plate, Ontong-Java plateau

분할 파형 역산을 사용한 서태평양 지역 S파 속도 및 방사 이방성 구조 연구

박지훈1 · 장성준1,* · Michael Witek2

1강원대학교 지구물리학과
2미국 로스 알라모스 국립 연구소

요 약

서태평양에 위치한 총 173개의 지진 관측소에서 획득한 2,026개의 지진 자료에 분할 파형 역산을 적용하여 서태평양 지역 맨틀 전이대 깊이까지 S파 등방성 속도 및 방사 이방성에 대한 연구를 수행했다. 그 결과 필리핀해판의 경우 페러스-벨라 분지(Parece-Vela basin)에서 고속도 이상이 30 km 깊이까지 나타나는 것에 비해 서필리핀 분지(West Philippine basin)에서 고속도 이상이 50 km 깊이까지 유지되었다. 페러스-벨라 분지 하부 약 80 km 깊이부터 나타나는 저속도 이상이 깊이가 깊어짐에 따라 서필리핀 분지로 확장되는 경향을 보였는데 이는 페러스-벨라 분지와 서필리핀 분지 사이의 연령차이에 의한 것으로 보인다. 또한 캐롤라인 해저 산열(Caroline seamount chain) 및 캐롤라인 판의 하부에서 강한 저속도 이상이 약 200 km 깊이까지 보인다. 방사 이방성 모델의 경우 서태평양에서 전반적으로 양의 이방성에 우세하게 나타났으며 페러스-벨라 분지에서 약 50 km 깊이까지, 마리아나 해구를 따라 섭입하는 태평양판의 약 220 km 깊이부터 음의 이방성이 관측되었다. 캐롤라인 해저산열 하부 약 200 km 깊이까지 강한 양의 이방성이 나타났는데 이는 해저산열을 형성한 플룸과 이동하는 태평양판 사이에 발생한 끌림(drag)에 의한 것으로 보인다. 온통-자바 해대(Ontong-Java plateau) 지역 하부에서는 40 ~ 180 km 깊이에서 고속도 이상이 발견되었으며, 이는 탈수된 플룸 물질의 부착으로 인한 비정상적으로 두꺼운 암석권의 존재를 나타낸다.

주요어 분할 파형 역산, 방사 이방성, 서태평양, 필리핀해판, 캐롤라인판, 온통-자바 해대

Article

Research Paper

Econ. Environ. Geol. 2023; 56(4): 365-384

Published online August 30, 2023 https://doi.org/10.9719/EEG.2023.56.4.365

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

S-velocity and Radial Anisotropy Structures in the Western Pacific Using Partitioned Waveform Inversion

Ji-hoon Park1, Sung-Joon Chang1,*, Michael Witek2

1Department of Geophysics, Kangwon National University, Chuncheon, South Korea
2Los Alamos National Lab, New Mexico, USA

Correspondence to:*sjchang@kangwon.ac.kr

Received: June 5, 2023; Revised: July 27, 2023; Accepted: August 7, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

We applied the partitioned waveform inversion to 2,026 event data recorded at 173 seismic stations from the Incorporated Research Institutions for Seismology Data Managing Center and the Ocean Hemisphere network Project to estimate S-wave velocity and radial anisotropy models beneath the Western Pacific. In the Philippine Sea plate, high-Vs anomalies reach deeper in the West Philippine basin than in the Parece-Vela basin. Low-Vs anomalies found at 80 km below the Parece-Vela basin extend deeper into the West Philippine Basin. This velocity contrast between the basins may be caused by differences in lithospheric age. Low-Vs anomalies are observed beneath the Caroline seamount chain and the Caroline plate. Overall positive radial anisotropy anomalies are observed in the Western Pacific, but negative radial anisotropy is found at > 220 km depth on the subducting plate along the Mariana trench and at ~50 km in the Parece-Vela basin. Positive radial anisotropy is found at > 200 km depth beneath the Caroline seamount chain, which may indicate the 'drag' between the plume and the moving Pacific plate. High-Vs anomalies are found at 40 ~ 180 km depth beneath the Ontong-Java plateau, which may indicate the presence of unusually thick lithosphere due to underplating of dehydrated plume material.

Keywords partitioned waveform inversion, radial anisotropy, Western Pacific, Philippine Sea plate, Caroline plate, Ontong-Java plateau

분할 파형 역산을 사용한 서태평양 지역 S파 속도 및 방사 이방성 구조 연구

박지훈1 · 장성준1,* · Michael Witek2

1강원대학교 지구물리학과
2미국 로스 알라모스 국립 연구소

Received: June 5, 2023; Revised: July 27, 2023; Accepted: August 7, 2023

요 약

서태평양에 위치한 총 173개의 지진 관측소에서 획득한 2,026개의 지진 자료에 분할 파형 역산을 적용하여 서태평양 지역 맨틀 전이대 깊이까지 S파 등방성 속도 및 방사 이방성에 대한 연구를 수행했다. 그 결과 필리핀해판의 경우 페러스-벨라 분지(Parece-Vela basin)에서 고속도 이상이 30 km 깊이까지 나타나는 것에 비해 서필리핀 분지(West Philippine basin)에서 고속도 이상이 50 km 깊이까지 유지되었다. 페러스-벨라 분지 하부 약 80 km 깊이부터 나타나는 저속도 이상이 깊이가 깊어짐에 따라 서필리핀 분지로 확장되는 경향을 보였는데 이는 페러스-벨라 분지와 서필리핀 분지 사이의 연령차이에 의한 것으로 보인다. 또한 캐롤라인 해저 산열(Caroline seamount chain) 및 캐롤라인 판의 하부에서 강한 저속도 이상이 약 200 km 깊이까지 보인다. 방사 이방성 모델의 경우 서태평양에서 전반적으로 양의 이방성에 우세하게 나타났으며 페러스-벨라 분지에서 약 50 km 깊이까지, 마리아나 해구를 따라 섭입하는 태평양판의 약 220 km 깊이부터 음의 이방성이 관측되었다. 캐롤라인 해저산열 하부 약 200 km 깊이까지 강한 양의 이방성이 나타났는데 이는 해저산열을 형성한 플룸과 이동하는 태평양판 사이에 발생한 끌림(drag)에 의한 것으로 보인다. 온통-자바 해대(Ontong-Java plateau) 지역 하부에서는 40 ~ 180 km 깊이에서 고속도 이상이 발견되었으며, 이는 탈수된 플룸 물질의 부착으로 인한 비정상적으로 두꺼운 암석권의 존재를 나타낸다.

주요어 분할 파형 역산, 방사 이방성, 서태평양, 필리핀해판, 캐롤라인판, 온통-자바 해대

    Fig 1.

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    Figure 1.Topographic features of the study area (top), and age distribution of the oceanic lithosphere (bottom, Müller et al., 2008), respectively. Black dashed lines represent the tectonic plate boundaries (Bird, 2003).
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 2.

    Download
    Figure 2.Distributions of stations and events, which are indicated by triangles and circles, respectively.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 3.

    Download
    Figure 3.The example of full-waveform fitting at different periods for three-component waveforms (left). The gray dashed, red solid, and black solid lines represent initial and final synthetic seismograms, and observed ones, respectively. The example of the 1-D models from waveform fitting (right). Blue and orange solid lines on the right panel represent the path-averaged 1-D profiles of the isotropic S-velocity and radial anisotropy, respectively.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 4.

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    Figure 4.Checkerboard tests results for the isotropic S-velocity model at various depths.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 5.

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    Figure 5.Checkerboard tests results for radial anisotropy at various depths.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 6.

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    Figure 6.Cross sections of checkerboard test results for (a) the isotorpic S-velocity perturbations and (b) radial anisotropy perturbations. The vertical sections are along the gray lines on the left-bottom panel.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 7.

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    Figure 7.Tomographic results for the isotropic S-velocity perturbations at various depths. The red quadrangle on the lower right panel represents the area for the results.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 8.

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    Figure 8.Tomographic results for radial anisotropy perturbations at various depths. The red quadrangle on the lower right panel represents the area for the results.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 9.

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    Figure 9.Cross sections of isotropic S-velocity (middle) and radial anisotropy perturbations (bottom) beneath the study area on the top. The black solid lines at the top of each panel represent topography along each line. WPB, West Philippine Basin; KPR, Kyushu-Palau Ridge; PVB, Parece-Vela Basin; MT, Mariana Tranch.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 10.

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    Figure 10.Tomographic results for the isotropic S-velocity perturbations at various depths. The red quadrangle on the lower right panel represents the area for the results.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 11.

    Download
    Figure 11.Tomographic results for radial anisotropy perturbations at various depths. The red quadrangle on the lower right panel represents the area for the results.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365

    Fig 12.

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    Figure 12.Cross sections of isotropic S-velocity (middle) and radial anisotropy perturbations (bottom) beneath the study area on the top. The black solid lines at the top of each panel represent topography along each line. WCB, West Caroline Basin; ER, Eauripik rise; ECB, East Caroline Basin; OJP, Ontong-Java Plateau; CR, Caroline Ridge; CS, Caroline Sesmout chain.
    Economic and Environmental Geology 2023; 56: 365-384https://doi.org/10.9719/EEG.2023.56.4.365
    KSEEG
    Oct 29, 2024 Vol.57 No.5, pp. 473~664
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