TY - JOUR T1 - A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Hawaiian Ridge: 1 JF - Journal of Geophysical Research: Solid Earth Y1 - 2023 A1 - MacGregor, B. G. A1 - Dunn, R. A. A1 - Watts, A. B. A1 - Xu, C. A1 - Shillington, D. J. KW - Hawaiian ridge KW - lithospheric flexure KW - marine gravity KW - plate loading KW - seismic tomography KW - volcano structure AB - The Hawaiian Ridge has long been a focus site for studying lithospheric flexure due to intraplate volcano loading, but crucial load and flexure details remain unclear. We address this problem using wide-angle seismic refraction and reflection data acquired along a ∼535-km-long profile that intersects the ridge between the islands of Maui and Hawai'i and crosses 80–95 Myr-old lithosphere. A tomographic image constructed using travel time data of several seismic phases reveals broad flexure of Pacific oceanic crust extending up to ∼200–250 km either side of the Hawaiian Ridge, and vertically up to ∼6–7 km. The P-wave velocity structure, verified by gravity modeling, reveals that the west flank of Hawaii is comprised of extrusive lavas overlain by volcanoclastic sediments and a carbonate platform. In contrast, the Hāna Ridge, southeast of Maui, contains a high-velocity core consistent with mafic or ultramafic intrusive rocks. Magmatic underplating along the seismic line is not evident. Reflectors at the top and bottom of the pre-existing oceanic crust suggest a ∼4.5–6 km crustal thickness. Simple three-dimensional flexure modeling with an elastic plate thickness, Te, of 26.7 km shows that the depths to the reflectors beneath the western flank of Hawai'i can be explained by volcano loading in which Maui and the older islands in the ridge contribute ∼43% to the flexure and the island of Hawai'i ∼51%. Previous studies, however, revealed a higher Te beneath the eastern flank of Hawai'i suggesting that isostatic compensation may not yet be complete at the youngest end of the ridge. VL - 128 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2023JB027218 N1 - _eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1029/2023JB027218 ER - TY - JOUR T1 - A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure of the Emperor Seamounts at Jimmu Guyot JF - Journal of Geophysical Research: Solid Earth Y1 - 2022 A1 - Xu, C. A1 - Dunn, R. A. A1 - Watts, A. B. A1 - Shillington, D. J. A1 - Grevemeyer, I. A1 - Gómez de la Peña, L. A1 - Boston, B. B. KW - Emperor Seamounts KW - gravity modeling KW - oceanic crust KW - plate flexure KW - seamount structure KW - seismic tomography AB - The intraplate Hawaiian-Emperor Seamount Chain has long been considered a hotspot track generated by the motion of the Pacific plate over a deep mantle plume, and an ideal feature therefore for studies of volcanic structure, magma supply, plume-crust interaction, flexural loading, and upper mantle rheology. Despite their importance as a major component of the chain, the Emperor Seamounts have been relatively little studied. In this paper, we present the results of an active-source wide-angle reflection and refraction experiment conducted along an ocean-bottom-seismograph (OBS) line oriented perpendicular to the seamount chain, crossing Jimmu guyot. The tomographic P wave velocity model, using ∼20,000 travel times from 26 OBSs, suggests that there is a high-velocity (>6.0 km/s) intrusive core within the edifice, and the extrusive-to-intrusive ratio is estimated to be ∼2.5, indicating that Jimmu was built mainly by extrusive processes. The total volume for magmatic material above the top of the oceanic crust is ∼5.3 × 104 km3, and the related volume flux is ∼0.96 m3/s during the formation of Jimmu. Under volcanic loading, the ∼5.3-km-thick oceanic crust is depressed by ∼3.8 km over a broad region. Using the standard relationships between Vp and density, the velocity model is verified by gravity modeling, and plate flexure modeling indicates an effective elastic thickness (Te) of ∼14 km. Finally, we find no evidence for large-scale magmatic underplating beneath the pre-existing crust. VL - 127 UR - https://onlinelibrary.wiley.com/doi/abs/10.1029/2021JB023241 N1 - _eprint: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2021JB023241 ER -