ridge_spreading
plain-language theorem explainer
Ridge spreading velocity is defined as the reference seismic velocity scale divided by phi to the ninth. Geologists applying Recognition Science to plate tectonics would cite this when locating boundary speeds on the phi-ladder. It is a direct definition that supplies the base value unfolded in the module's ratio and inequality theorems.
Claim. The ridge spreading velocity equals $c_ {seismic} / phi^9$, where $c_{seismic}$ denotes the reference seismic velocity scale.
background
The Plate Boundary Dynamics module places subduction and ridge velocities on the phi-ladder that follows from the Recognition Science forcing chain. The upstream definition c_seismic sets the reference seismic velocity scale to 1 in RS-native units. Ridge spreading is assigned the slower position at c_seismic / phi^9 while subduction occupies c_seismic / phi^7, yielding the ratio phi^2.
proof idea
Direct definition that assigns the expression c_seismic / phi^(9 : ℕ). No lemmas are invoked; the value is supplied for unfolding in the downstream ratio and inequality statements.
why it matters
This definition supplies the ridge_spreading field inside the PlateBoundaryDynamicsCert structure, which records the phi^2 ratio, the ridge-slower inequality, and positivity conditions. It completes the geology row of the phi-ladder in the Recognition framework, consistent with the phi fixed point and eight-tick octave scaling. The Wilson cycle lower bound interval is built directly on this assignment.
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