| Summary: | Abstract Previous studies attribute asymmetries across the East Pacific Rise to horizontal temperature or pressure gradients in the deep asthenosphere caused by the Pacific Superswell, which, however, cannot explain asymmetries observed across the Juan de Fuca Ridge. Here, we provide seismic evidence that the asymmetric seafloor depth across the Juan de Fuca Ridge is primarily caused by thermal buoyancy due to lithospheric heating and thinning. Based on a seismic model generated from Rayleigh wave measurements, we demonstrate that the seafloor depth on the western flank of the ridge, which is shallower ( > 150 m) than the prediction from the plate age, agrees with the relatively younger apparent thermal age inferred from the seismic data, whereas the buoyancy of the deeper asthenosphere alone can only account for <25% of the rise. On the eastern flank, both plate age and apparent thermal age are consistent with observed seafloor depth.
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