Vertical component data from 206 broadband seismometer stations from Korean networks Korean Institute of Geoscience and Mineral Resources and Korea Meteorological Administration, the Japanese F‐net network, and the Chinese New China Digital Seismograph Network and Northeast China Extended Seismic Array network are collected for the year 2011, and the ambient seismic noise is analyzed. Rayleigh wave group velocity distribution maps are created in the period range 10 to 70 s. Our results are largely consistent with previous studies of the area but provide greater detail in the Korean peninsula and the Sea of Japan. Low group velocities are observed in the Ulleung basin, and the Chubu‐Kanto and Kyushu regions in Japan. At 10 s period, sediment basins in the Sea of Japan appear as low group velocity regions relative to higher group velocity continental regions. At periods longer than 40 s, a low group velocity region emerges in the Ulleung basin region, and is bounded by the Korean peninsula.

Clusters of Cenozoic volcanoes are found in Korea and Northeast China away from plate boundaries, but the mechanisms responsible for their formation is still unknown. To resolve this issue, we derive an S‐wave velocity model of the upper mantle structure beneath East Asia using 131,947 S‐wave relative traveltimes from 974 earthquakes recorded at 1,948 seismic stations in China, Korea, Taiwan, and Japan. Our results show that low‐velocity anomalies beneath Mt. Baekdu (Changbaishan) and Jeju Island extend to the bottom of the mantle transition zone (MTZ) through slab gaps in the stagnant Pacific slab. On the other hand, low‐velocity anomalies beneath the Datong volcanic field are observed to connect to the edge of the stagnant Pacific slab, which may be attributed to subduction‐triggered upwelling or deep dehydration from the hydrous MTZ perturbed by subducting slabs. Furthermore, tilted high‐velocity anomalies are found all the way down to the MTZ beneath the Great Xing'an Range and the Songliao basin, which may indicate delaminated lithosphere. The intraplate volcanoes north of the Songliao basin, such as the Wudalianchi and Halaha volcanoes, are located just above the delaminated bodies, thereby implying that decompression melting after delamination may be responsible for the intraplate volcanoes. Therefore, the dominant origin of intraplate volcanoes in East Asia may be subduction‐related hot upwelling, complemented by shallow origins such as edge‐driven convection and lithospheric delamination.

We measured Rayleigh wave group velocity dispersion curves from station pair cross correlations of continuous broadband data from 1,082 seismic stations in regional networks across China, Korea, and Japan. The dispersion curves are localized in the period range 6–40 s to produce group velocity maps, which we then combine with group velocity data in the period range 50–133 s from the global dispersion model of Ma et al. (2014, https://doi.org/10.1093/gji/ggu246). Cluster analysis performed on the local dispersion curves reveals distinct tectonic regions and provides a new way of estimating the number of regions needed to describe a surface wave dispersion data set. We inverted the centroid dispersion curves corresponding to each cluster for a new set of reference models. We used a combination of teleseismic receiver functions and Moho depths from the LITHO1.0 model to create a 3‐D Moho depth reference model and then constructed a 3‐D S velocity model by jointly inverting group velocities with localized phase velocities in the period range 28.57–200 s, also from Ma et al. (2014, https://doi.org/10.1093/gji/ggu246). The cluster analysis and comparisons with other regional models provide evidence for a broad region of deformed lithosphere in East Asia. We image high velocities in the Yangtze and Ordos cratons and low velocities underneath the East Sea (Sea of Japan), and we find that a low‐velocity zone in the midcrust is appropriate for Tibet. The model we present is intended as an alternative reference model that fits a broader range of periods to be used for further studies of regional geophysical phenomena.

The field of seismic tomography has advanced to the point that researchers have been able to determine the isotropic velocity structure of the Earth on a global and regional scale with increasing consistency despite varying methodologies and data sets. Tomographic studies have succeeded in imaging and interpreting large-scale structures such as subducting slabs and upwelling plumes across the globe (e.g.,

Seismic radial anisotropy is a crucial tool to help constrain flow in the Earth's mantle. However, Earth structure beneath the oceans imaged by current 3‐D radially anisotropic mantle models shows large discrepancies. Here, we provide constraints on the radially anisotropic upper mantle structure beneath the Pacific by waveform modeling and subsequent inversion. Specifically, we objectively evaluate three 3‐D tomography mantle models which exhibit varying distributions of radial anisotropy through comparisons of independent real data sets with synthetic seismograms computed with the spectral‐element method. The data require an asymmetry at the East Pacific Rise (EPR) with stronger positive radial anisotropy ξ = VSH2VSV2 = 1.13–1.16 at ∼100 km depth to the west of the EPR than to the east (ξ = 1.11–1.13). This suggests that the anisotropy in this region is due to the lattice‐preferred orientation of anisotropic mantle minerals produced by shear‐driven asthenospheric flow beneath the South Pacific Superswell. Our new radial anisotropy constraints in the Pacific show three distinct positive linear anomalies at ∼100 km depth. These anomalies are possibly related to mantle entrainment at the Nazca‐South America subduction zone, flow at the EPR and from the South Pacific Superswell and shape‐preferred orientation (SPO) of melt beneath Hawaii. Radial anisotropy reduces with lithospheric age to ξ < 1.05 in the west at ∼100 km depth, which possibly reflects a deviation from horizontal flow as the mantle is entrained with subducting slabs, a change in temperature or water content that could alter the anisotropic olivine fabric or the SPO of melt.