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

Abstract

AbstractWe 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 ∼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.