Global P-Wave and Joint S-Wave Tomography in the North Pacific: Implications for Slab Geometry and Evolution

We presented two high-resolution, three-dimensional (3D) global P- and joint S-wave velocity models of the whole mantle with a particular focus on the North Pacific realm using our new global tomographic inversion method. The 3D ray tracing based on data-adaptive block parameterization was implemented to calculate similar to 17 million body-wave absolute travel times and ray paths of multiple classes (e.g., P, S, PP, SSS, PcP, ScSScS, Pdiff, and PKP) recorded by local networks in China, Alaska, and global stations. Rayleigh wave data at 40-250 s was also incorporated for resolution improvement. Compared to previous models, especially at long spatial wavelengths, our new models better exhibited rich variations in the properties of slabs and cratons subducting/subducted into the mantle. The Kurile-Kamchatka-Aleutian arc exhibits a distinct and well-defined pattern of long linear bands characterized by high velocity (high-Vp, high-Vs) anomalies. These anomalies descend continuously from the subduction zone and then extend horizontally at the mantle transition zone (MTZ) beneath the Bering Sea, Japan Sea, or alternatively penetrate into the lower mantle below the Okhotsk Sea. We observed there was no slab-related gap trapped on top of the MTZ beneath the Alaska Peninsula, which was possibly relevant for the subduction of the extinct Kula and Pacific Plates described in previous studies. A further unexpected discovery, deduced from the slab's location and tectonic history, was the identification of a high-Vp anomaly running parallel to the plate boundary in the Aleutian forearc region, which was considered as an integral part of the Kula slab. Plain Language Summary The Circum-North Pacific contains an active North-Northwestward subduction zone of the ancient Izanagi and Kula Plates and the present Pacific Plate during the Late Mesozoic to Cenozoic. This successive subduction system leads to complex plate tectonics characterized by substantial topographic variations, widespread subduction zones, abundant intraplate volcanic activities, and ancient craton lithospheric deformation. Here we image high-resolution P- and S-wave velocity models, which were inverted by our updated global tomographic method using data containing more than 17 million body and surface wave measurements. Our models indicate no gaps at the top of the mantle transition zone, and it differs from the previous studies beneath the Aleutian Arc. In addition, two parallel high-Vp belts are imaged on both sides of the Aleutian Arc between similar to 300 and 1,000 km depth, which were considered as part of the remnant Kula slab and present Pacific slab. These findings provide both a good understanding of the slab geometry and evolution associated with multiple plate subduction in the North Pacific subduction zone and an example to understand the way how the Earth's interior works.