Surface wave tomography for the Pacific Ocean incorporating seafloor seismic observations and plate thermal evolution

• Published in: Earth and planetary science letters Vol. 510; pp. 116 - 130
• Main Authors: Isse, Takehi, Kawakatsu, Hitoshi, Yoshizawa, Kazunori, Takeo, Akiko, Shiobara, Hajime, Sugioka, Hiroko, Ito, Aki, Suetsugu, Daisuke, Reymond, Dominique
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.03.2019
• Subjects: oceanic upper mantle; Pacific Ocean; seafloor-age dependence; surface wave tomography; Pacific Ocean; surface wave tomography; oceanic upper mantle; seafloor-age dependence
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2018.12.033

Using broadband seismic waveforms recorded on the seafloor by more than 200 broadband ocean bottom seismometers, as well as those on land, we measured the phase speed dispersions of Love and Rayleigh waves up to the 4th higher mode to determine the three-dimensional radially anisotropic shear-wave speed structure in the upper mantle beneath the Pacific Ocean. The fastest anomalies at depths shallower than 100 km were located beneath southeast of the Shatsky Rise and strong radial anisotropy was located in the central Pacific at depths of 100–200 km. The isotropic shear-wave speed structures showed age dependence. From the age-bin-averaged shear-wave speed profiles and a half-space cooling model, we estimated the thermo-speed relationship for the Pacific Plate to construct a reference age-dependent shear-wave speed model, which was further used as an initial model for tomography iteration. Deviation maps in the Pacific Ocean from the reference model indicated that large negative residuals, which may be due to partial melting, anelasticity, and/or added heat from mantle plumes, were located along the ridges and beneath hotspots, and that large positive residuals were found beneath the northwestern Pacific Ocean. The use of an age-dependent reference model, as well as the incorporation of OBS data, greatly improves the accuracy of local phase speed estimates in tomography, as evident from a direct comparison with in situ array measurements. •Using seafloor and land data, we obtained the upper mantle structure in the Pacific.•Isotropic shear wave structure shows clear age dependence.•Reference age-dependent shear wave model is used for tomography inversion.•Large residuals from the age-dependent model are located beneath the hotspots.•Seafloor data and age-dependent model improves the accuracy of tomography.