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This study presents the velocity structures of the seafloor sediment across the Pacific using teleseismic body waves recorded by arrays of ocean bottom seismometers (OBSs). We apply the method inverting the multicomponent stacked autocorrelation functions and radial-component waveform of teleseismic body waves. We analyze OBSs distributed across the Pacific Ocean, through a wide range of water depths and equipped with various sensor types. The inverted models agreeing with measurements of seafloor drilling samples demonstrate the broad applicability of employing the inversion method to resolve sediment thicknesses ranging from <100 m to a few kilometers. In addition to various broad-band OBSs, we confirm our method works also for short-period sensors, since our retrieved the model using data from a short-period sensor in Northeast Japan agrees with active-source seismic survey analyses. The constrained models show various numbers of intrasediment discontinuities across different locations. Furthermore, the newly characterized sediment models have higher values of P -wave to S -wave velocity ratio (⁠|${{V}_P}$| / |${{V}_S}$|⁠) than the previously known scaling relationships, which suggests a larger effect of sediment-layer reverberation on the body-wave analysis than we have anticipated. The sediment velocity models obtained in this study produce Rayleigh-wave admittances that are consistent with those in previous studies but with much finer structural details within the sediment layer. The reverberation waveform inversion method will enable improved predictions of the impact of the water and sediment layers in body-wave records from existing and future OBS observations. [ABSTRACT FROM AUTHOR]

Increasing deployment of dense arrays has facilitated detailed structure imaging for tectonic investigation, hazard assessment and resource exploration. Strong velocity heterogeneity and topographic changes have to be considered during passive source imaging. However, it is quite challenging for ray‐based methods, such as Kirchhoff migration or the widely used teleseismic receiver function, to handle these problems. In this study, we propose a 3‐D passive source reverse time migration strategy based on the spectral element method. It is realized by decomposing the time reversal full elastic wavefield into amplitude‐preserved vector P and S wavefields by solving the corresponding weak‐form solutions, followed by a dot‐product imaging condition to get images for the subsurface structures. It enables us to use regional 3‐D migration velocity models and take topographic variations into account, helping us to locate reflectors at more accurate positions than traditional 1‐D model‐based methods, like teleseismic receiver functions. Two synthetic tests are used to demonstrate the advantages of the proposed method to handle topographic variations and complex velocity heterogeneities. Furthermore, applications to the Laramie array data using both teleseismic P and S waves enable us to identify several south‐dipping structures beneath the Laramie basin in southeast Wyoming, which are interpreted as the Cheyenne Belt suture zone and agree with, and improve upon previous geological interpretations. Plain Language Summary: Increasing deployment of dense arrays has allowed detailed structure imaging. However, traditional ray‐based migration methods or 1‐D velocity model‐based receiver function methods may greatly degrade the imaging quality without considering the full wavefield propagation effect and velocity heterogeneities. Therefore, in this study, we develop a 3‐D passive source migration based on the spectral element method, which is capable of handling topographic variations as well as complex velocity heterogeneities for real data applications. Several synthetic tests and applications to the Laramie array data using both teleseismic P and S waves are used to demonstrate the capability of our method to image complex structures, such as subduction and suture zones. Key Points: A 3‐D passive source reverse time migration based on the spectral element method is proposed to image complex structuresAmplitude‐preserved vector P and S wavefields are accurately decomposed by solving corresponding weak‐form solutionsSeveral south‐dipping structures can be identified from P and S migration results beneath the Laramie basin which are interpreted as the Cheyenne Belt suture zone [ABSTRACT FROM AUTHOR]

A study of the seismograms from a seismic array in the Japanese islands offers evidence for 920-km deep seismic discontinuity in the Earth's mantle below the Tonga subduction zone. The discontinuity may be attributed to a change in the mantle's chemical content or the signature of the garnet layer of the subducted zone. The discontinuity also exists below subduction areas in the Flores and Japan seas.