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Abstract 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. TheP‐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,T_e, 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 higherT_ebeneath the eastern flank of Hawai'i suggesting that isostatic compensation may not yet be complete at the youngest end of the ridge. 

Abstract The Hawaiian Ridge, a classic intraplate volcanic chain in the Central Pacific Ocean, has long attracted researchers due to its origin, eruption patterns, and impact on lithospheric deformation. Thought to arise from pressure‐release melting within a mantle plume, its mass‐induced deformation of Earth's surface depends on load distribution and lithospheric properties, including elastic thickness (T_e). To investigate these features, a marine geophysical campaign was carried out across the Hawaiian Ridge in 2018. Westward of the island of O'ahu, a seismic tomographic image, validated by gravity data, reveals a large mass of volcanic material emplaced on the oceanic crust, flanked by an apron of volcaniclastic material filling the moat created by plate flexure. The ridge adds ∼7 km of material to pre‐existing ∼6‐km‐thick oceanic crust. A high‐velocity and high‐density core resides within the volcanic edifice, draped by alternating lava flows and mass wasting material. Beneath the edifice, upper mantle velocities are slightly higher than that of the surrounding mantle, and there is no evidence of extensive magmatic underplating of the crust. There is ∼3.5 km of downward deflection of the sediment‐crust and crust‐mantle boundaries due to flexure in response to the volcanic load. At Ka'ena Ridge, the volcanic edifice's height and cross‐sectional area are no more than half as large as those determined at Hawai'i Island. Together, these studies confirm that volcanic loads to the west of Hawai'i are largely compensated by flexure. Comparisons to the Emperor Seamount Chain confirm the Hawaiian Ridge's relatively stronger lithospheric rigidity. 

Abstract 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 tomographicPwave 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 Vpand density, the velocity model is verified by gravity modeling, and plate flexure modeling indicates an effective elastic thickness (T_e) of ∼14 km. Finally, we find no evidence for large‐scale magmatic underplating beneath the pre‐existing crust. 

Abstract The Hawaiian‐Emperor seamount chain in the Pacific Ocean has provided fundamental insights into hotspot generated intraplate volcanism and the long‐term strength of oceanic lithosphere. However, only a few seismic experiments to determine crustal and upper mantle structure have been carried out on the Hawaiian Ridge, and no deep imaging has ever been carried out along the Emperor seamounts. Here, we present the results of an active source seismic experiment using 29 Ocean‐Bottom Seismometers (OBS) carried out along a strike profile of the seamounts in the region of Jimmu and Suiko guyots. Joint reflection and refraction tomographic inversion of the OBS data show the upper crust is highly heterogeneous withPwave velocities <4–5 km s⁻¹, which are attributed to extrusive lavas and clastics. In contrast, the lower crust is remarkably homogeneous with velocities of 6.5–7.2 km s⁻¹, which we attribute to oceanic crust and mafic intrusions. Moho is identified by a strongPmParrival at offsets of 20–80 km, yielding depths of 13–16 km. The underlying mantle is generally homogeneous with velocities in the range 7.9–8.0 km s⁻¹. The crust and mantle velocity structure has been verified by gravity modeling. While top of oceanic crust prior to volcano loading is not recognized as a seismic or gravity discontinuity, flexural modeling reveals a ∼5.0–5.5 km thick preexisting oceanic crust that is overlain by a ∼8 km thick volcanic edifice. Unlike at the Hawaiian Ridge, we find no evidence of magmatic underplating.