Quasi-Cartesian finite-difference computation of seismic wave propagation for a three-dimensional sub-global model

Takenaka, Hiroshi; Komatsu, Masanao; Toyokuni, Genti; Nakamura, Takeshi; Okamoto, Taro

doi:10.1186/s40623-017-0651-1

Cited by 8 publications

(10 citation statements)

References 26 publications

(20 reference statements)

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“…To address this problem, a flexible grid method that arranges grid nodes at irregular intervals (Zhao, 2009) and a method that moves the study region to the equator by global coordinate transformation (Gupta et al, 2009; Kobayashi & Zhao, 2004) have been proposed. In this study, we adopt one of the latter methods using the transformation from equatorial to ecliptic coordinates, which is proposed in the field of seismic waveform modeling (i.e., the quasi‐Cartesian approach) (Takenaka et al, 2017). Details of the coordinate transformation are given in Appendix A.…”

Section: Methodsmentioning

confidence: 99%

“…Following Takenaka et al (2017), we assume that the location (longitude, latitude) of a reference point and an arbitrary point in the equatorial coordinates are represented by (γ′, ε) and (α′, δ), respectively ( Figure S22a). We define the position of the arbitrary point to be (α, δ) when rotated by an angle ψ around the Earth's axis, and the reference point would then be (90°, ε) ( Figure S22b).…”

Section: Appendix A: Coordinate Transformationmentioning

confidence: 99%

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P Wave Tomography Beneath Greenland and Surrounding Regions: 1. Crust and Upper Mantle

2020

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We study the 3-D P wave velocity (Vp) structure of the crust and upper mantle beneath Greenland and surrounding regions using the latest P wave arrival time data. The Greenland Ice Sheet Monitoring Network (GLISN), initiated in 2009, is an international project for seismic observation in these regions using 34 stations. We use a regional seismic tomography method to simultaneously invert P wave arrival times of local earthquakes and P wave relative traveltime residuals of teleseismic events. These data are extracted from the ISC-EHB catalog; however, for the teleseismic data, we picked new arrival times from seismograms using a cross-correlation method. Our tomographic results clearly reveal the Iceland plume, the Jan Mayen plume, and a newly discovered "Svalbard plume," which merge together in the mantle transition zone. A high-Vp body exists beneath the Greenland Sea, which might act as an obstacle against the rising Svalbard plume. Furthermore, our results reveal a remarkable low-Vp anomaly elongated in the NW-SE direction at depths ≤250 km beneath central Greenland, which is connected with the Iceland and Jan Mayen hotspots. Although previous studies have suggested a similar feature, our result is the first to show the low-Vp zone existing at all depths in the Greenland lithosphere, and its spatial distribution coincides with a high heat flux region. These characteristics indicate that the low-Vp zone reflects residual heat from the Iceland plume when the Greenland lithosphere passed over this plume at~80-20 Ma. Our results also indicate the possible existence of residual heat from the Jan Mayen plume. Plain Language Summary Greenland is a stable land mass that has preserved~4 Gyr of Earth's history. In its vicinity, there are the Mid-Atlantic Ridge, the Iceland and Jan Mayen hotspots, and a geothermal area in Svalbard, which indicate the complexity of this region. We apply seismic tomography to analyze the latest data recorded by a new seismograph network, and we obtain detailed 3-D images of the crust and upper mantle. Our results clearly image the conduit-like Iceland plume, the Jan Mayen plume, and a newly discovered "Svalbard plume," which merge together in the mantle transition zone. These new findings will improve our understanding of the tectonic and thermal evolution of this region. We also find a low seismic velocity zone running in the NW-SE direction beneath central Greenland, which is connected with the Iceland and Jan Mayen hotspots. This zone is located within the Greenlandic plate, and its spatial distribution agrees well with an area of high geothermal heat flux. These results suggest that the low-velocity zone reflects residual heat from the Iceland plume when the Greenlandic plate passed over the plume at~80-20 Ma. Our model further suggests a possible heat track left by the Jan Mayen plume.

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Section: Methodsmentioning

confidence: 99%

Section: Appendix A: Coordinate Transformationmentioning

confidence: 99%

P Wave Tomography Beneath Greenland and Surrounding Regions: 1. Crust and Upper Mantle

2020

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“…We conduct a global coordinate transformation of the study region by moving its center to the equator (Takenaka et al, 2017;Toyokuni et al, 2020a), so that we can set 3-D grid nodes for the tomographic inversion uniformly both in the longitude and latitude directions. Following Toyokuni et al (2020a), we move the station SUMG (longitude, latitude)=(−38.461°, 72.574°) on the GrIS summit to a point on the equator   (90 , 0 ) E .…”

Section: Methodsmentioning

confidence: 99%

P‐Wave Tomography for 3‐D Radial and Azimuthal Anisotropy Beneath Greenland and Surrounding Regions

Toyokuni

Zhao

2021

Earth and Space Science

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Greenland is the largest island in the world whose land area spans over 20° in the central angle of the Earth. The surface-exposed rocks have preserved ∼4 billion years of Earth's history in the oldest part (Henriksen et al., 2009). However, the Greenland Ice Sheet (GrIS), covering 80% of the land area, has long hindered the geological study in the inland area. Greenland itself has low seismic activity and no known active volcanoes, but there are several hot springs on the east and west coasts of Greenland (Hjartarson & Armannsson, 2010) that coincide with Tertiary basalt outcrops. The Mid-Atlantic Ridge (MAR) is located on the eastern side of Greenland, where the North American plate and the Eurasian plate separate from each other, inducing very active seismicity. There are also three major hotspots (Iceland, Jan Mayen, and Svalbard) along the MAR, highlighting the tectonic activity of this region. Turing our eyes to the western side of Greenland,

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“…When we attempt to specify the study area located in high‐latitude regions such as Greenland using longitudinal and latitudinal ranges, a fan‐shaped area is cut out in the horizontal direction. Therefore, in this study, we apply a method that moves the center of the study region to the equator by a global coordinate transformation (Takenaka et al, 2017). We transform all earthquakes and seismic stations used from the equatorial to ecliptic coordinates so that the location (longitude, latitude) of a reference point in the study region is transformed to (90°, 0°).…”

Section: Methodsmentioning

confidence: 99%

P Wave Tomography Beneath Greenland and Surrounding Regions: 2. Lower Mantle

2020

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We study the 3-D P wave velocity (Vp) structure of the whole mantle beneath Greenland and surrounding regions using the latest P wave arrival time data. We use a new method of global seismic tomography by setting 3-D grid nodes densely in the study volume to enhance the resolution. We invert~5.6 million arrival times of P, pP, and PP waves from 16,257 earthquakes extracted from the ISC-EHB catalog, which were recorded at 12,549 seismic stations in the world. Our results reveal a hot plume rising from the core-mantle boundary beneath central Greenland, which is called the Greenland plume. This plume has the main conduit and two branches in the lower mantle, and the main conduit rises to the mantle transition zone (MTZ) beneath eastern Greenland, so it is distinguishable from the Iceland plume that appears to rise from a midmantle depth (~1,500 km) beneath Iceland. The Iceland plume itself is a powerful plume, but it may also be fed by hot mantle materials from three joints with other plumes: a branch of the Greenland plume at~1,500 km depth, a plume beneath Western Europe at~1,000 km depth, and the main conduit of the Greenland plume at the MTZ, leading to many active volcanoes in Iceland. We deem that the main conduit of the Greenland plume mixes with the Iceland plume incompletely and splits mainly into the Jan Mayen and Svalbard plumes in the upper mantle, which supply magma to the Jan Mayen hotspot and a geothermal area in western Svalbard, respectively. Plain Language Summary Greenland and its surrounding regions have many clues for understanding global-scale tectonics of the Earth. Seismic tomography is a well-established method for obtaining 3-D images of the underground structure by inverting a large number of seismic wave arrival times. We obtain detailed tomographic images of the whole mantle beneath Greenland and adjacent regions using the latest dataset. Our high-resolution results show that the so-called Iceland plume could be composed of two plumes. One is located directly beneath Iceland but rising from~1,500 km depth, which we call the Iceland plume. The other is rising from the core-mantle boundary beneath central Greenland, which we call the Greenland plume. The Greenland plume has the main conduit and two branches in the lower mantle, and the main conduit rises to the mantle transition zone beneath eastern Greenland. Although the Iceland plume itself is a powerful plume, it may also have three joints with other plumes: the main conduit and a branch of the Greenland plume, and a plume beneath Western Europe, resulting in many active volcanoes in Iceland. The main conduit of the Greenland plume may also supply magmas to the Jan Mayen hotspot and a geothermal area in western Svalbard.

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Quasi-Cartesian finite-difference computation of seismic wave propagation for a three-dimensional sub-global model

Cited by 8 publications

References 26 publications

P Wave Tomography Beneath Greenland and Surrounding Regions: 1. Crust and Upper Mantle

P Wave Tomography Beneath Greenland and Surrounding Regions: 1. Crust and Upper Mantle

P‐Wave Tomography for 3‐D Radial and Azimuthal Anisotropy Beneath Greenland and Surrounding Regions

P Wave Tomography Beneath Greenland and Surrounding Regions: 2. Lower Mantle

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