Abstract
Mid-ocean ridges with well developed median valleys are commonly the sites of large normal-faulting earthquakes1,2. A recent global study3–6 of the centroid depths and source mechanisms of such earthquakes has yielded two important conclusions: first, that all the largest mid-ocean ridge earthquakes occur beneath the inner floor of the median valley, and second, that the maximum thickness of the seismogenic layer increases with decreasing spreading rate. These results lend support to the hypothesis that the median valley arises from the necking of a strong, brittle lithosphere under horizontal extension7–9. Here we compare the global rate of seismic moment release along slowly spreading mid-ocean ridges with the rate predicted if widening of the median valley occurs entirely by seismogenic extension of the brittle lithosphere beneath the inner floor. We find that earthquakes account for no more than about 10–20% of the rate of plate separation across the central median valley.
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Solomon, S., Huang, P. & Meinke, L. The seismic moment budget of slowly spreading ridges. Nature 334, 58–60 (1988). https://doi.org/10.1038/334058a0
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DOI: https://doi.org/10.1038/334058a0
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