A simple model for the fault‐generated morphology of slow‐spreading mid‐oceanic ridges

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Abstract
We postulate that fluctuations in magmatic activity at mid‐oceanic ridges perturb the horizontal least principal stress across rift‐bounding normal faults, leading to alternating phases of magmatic accretion, which increases valley width, and tectonic extension, which results in the growth of inner rift wall topography. Fine‐scale bathymetrie surveys and earthquake fault plane solutions show that active normal faults at slow‐spreading ridges are moderately dipping (approximately 45°) planar features throughout the seismogenic oceanic lithosphere. A simple quantitative model that includes flexural deformation of a 10‐km‐thick elastic plate by slippage on 45° dipping normal faults can match the bathymetrie profiles across several slow‐spreading ridge segments. Comparison among dip distributions of normal‐faulting earthquakes at mid‐ocean ridges, in the trench‐outer rise region, and on continents suggests that most events from these three tectonic environments initiated at dips close to 45°, raising unanswered questions about the mechanical conditions under which the faults originated.