We present detailed 3-D images of whole mantle P-wave velocity structure beneath Southeast Asia and surrounding regions. The results are obtained by applying an updated global tomographic method to invert ~8 million P, pP, PP, PcP, and Pdiff arrival times from 23,587 earthquakes recorded at 14,136 stations distributed all over the world. Our tomographic model reveals a continuous, thin low-velocity (low-V) zone from the surface to the core-mantle boundary beneath the Hainan hotspot, which may reflect the Hainan plume that exists in the whole mantle. Beneath the Australian slab that has subducted into the lower mantle, a strong low-V anomaly is detected, which may reflect subslab hot mantle upwelling (SHMU) due to return flow of the slab subduction. Our model also shows the distinct shape of subducted slabs in the upper mantle and slab remnants in the lower mantle. In particular, a hole in the subducting Australian slab is revealed at depths of 280–430 km beneath eastern Java. The low-V anomaly in the mantle wedge above the Australian slab is connected with the SHMU through the slab hole, suggesting that mixture of the island arc magma and the SHMU may have caused huge eruptions of the Tambora and Rinjani volcanoes in eastern Java.

A detailed 3-D tomographic model of the whole mantle beneath the circum-Arctic region is obtained by applying an updated global tomography method to a large amount of P-wave arrival time data. Our model clearly shows the subducted Izanagi and Farallon slabs penetrating into the lower mantle beneath Eurasia and North America, respectively. In the region from Canada to Greenland, a giant stagnant slab lying below the 660-km discontinuity is revealed. Because this slab has a texture that seems to be due to subducted oceanic ridges, the slab might be composed of the Izanagi, Farallon, Kula and Vancouver slabs that had subducted during ~80−20 Ma. During that period, a complex rift system represented by division between Canada and Greenland was developed. The oceanic ridge subduction and hot upwelling in the big mantle wedge above the stagnant slab caused a tensional stress field, which might have induced these complex tectonic events.

We present the first 3-D images of P-wave radial anisotropy (RAN) and azimuthal anisotropy (AAN) down to 750-km depth beneath Greenland and surrounding regions. The results are obtained by applying a regional tomographic method to simultaneously invert P wave arrival times of 1,309 local events and P wave relative traveltime residuals of 7,202 teleseismic events, which were recorded mainly by the latest GLISN network. A high-velocity body located beneath northeast Greenland (NEG) to its offshore exhibits a strong negative RAN and a strong AAN with N-S to NE-SW oriented fast-velocity directions (FVDs). The FVDs are generally consistent with the direction of the fold axis of the Caledonian fold belt, which is considered as an outcrop of the NEG body on land. Beneath the Iceland, Jan Mayen, and Svalbard hotspots, a strong positive RAN and a negligible or weak AAN are revealed, which may reflect effects of upwelling mantle plumes. Among the three regions, a weak AAN with a constant FVD is only revealed beneath Iceland, which may reflect the existence of background mantle flow. The RAN and AAN features beneath the Labrador Sea, Davis Strait, and Baffin Bay suggest the following scenario on breakup between Greenland and Canada: the breakup was initiated at the Labrador Sea due to local mantle upwelling, but the northward propagation of the breakup was blocked by a strong high-velocity anomaly beneath Davis Strait; the opening of Baffin Bay might be caused passively by far-field plate forces.

We estimated the seismic attenuation (Q factor) of the Greenland Ice Sheet (GrIS) by comparing observed and theoretical Rayleigh waveforms. Observed waveforms are obtained by interfering with noise waveforms in vertical-component seismograms between stations, which belong to the latest broadband seismic network distributed throughout Greenland (GLISN network). Theoretical waveforms are calculated by parallel computation with the latest 3-D seismic waveform modeling. Comparing the observed waveforms with the theoretical waveforms at different Q factors reveals that GrIS has a low Q of QP, QS ≤ 50, indicating very high attenuation of seismic waves due to the ice. This study is the first to confirm the low Q factor of ice sheets via ultra-long-distance propagation (~several hundreds to 1,000 km). The Q factors obtained in this study are indispensable for estimating the thermal status of GrIS, as well as for interpreting the characteristics of seismic waveform that propagates through GrIS.

We study the 3-D P-wave velocity (Vp) structure of the lower 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, and currently operating 35 seismic stations. We use a new method of global-scale seismic tomography, which sets 3-D grid nodes densely in the study region to enhance the resolution. We invert ~5.8 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 stations in the world.  Our results reveal a hot plume rising from the core-mantle boundary beneath central Greenland, which is named “Greenland plume”. On the other hand, the Iceland plume rises from ~1500 km depth in the lower mantle. At depths < 1500 km, the Iceland plume might be supplied with hot mantle materials through narrow paths from a low-Vp region beneath the North Sea and/or from possible branches of the Greenland plume. We deem that, after the two plumes are joined together in the mantle transition zone (MTZ), the Greenland plume splits mainly into the Jan Mayen and Svalbard plumes in the upper mantle, supplying magmas to the Jan Mayen volcano and the geothermal area in western Svalbard, respectively. Our results also reveal a high-Vp body above the MTZ beneath northeastern Greenland. The lack of active volcanoes in Svalbard is probably due to this body obstructing the flow of the Greenland plume.

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, and currently operating 35 seismic stations. We use a regional-scale seismic tomography method to simultaneously invert both absolute P-wave arrival times of local earthquakes and P-wave relative travel-time residuals of teleseismic events. These data are extracted from the ISC-EHB catalog, but for the teleseismic events, we newly picked arrival times from seismograms using the cross-correlation analysis. In the tomographic inversion, the grid intervals in the longitudinal direction depend on the latitude in the polar regions, so we apply the coordinate transformation that moves the study region to the equator. Our results reveal a remarkable low-Vp anomaly elongated in the NW-SE direction at depths ≤ 250 km beneath central Greenland, which may reflect the residual heat when the Greenlandic plate passed over the Iceland plume at ~80−20 Ma. Although previous studies have suggested this feature, our results first show that the low-Vp zone is within the Greenlandic lithosphere and its spatial distribution agrees very well with the high crustal heat-flow regions. Our results also indicate possible existence of residual heat from the Jan Mayen plume.