A Ceiling on Seismic Moment from Fault Geometry, Rigidity, and the Shear Bound

This study computes the maximum seismic moment from stated inputs and places the result against both the published observational value and the density ceiling of Einstein-Cartan torsion gravity, in which spin-sourced torsion caps the effective density of neutron matter near 9.72e57 kilograms per cubic metre. The computation gives: largest scanned moment 1.20e+24 N m; corresponding moment magnitude 9.99; 1960 Chile moment for comparison 2.7e22 N m; factor above the Chile moment 44; radiated energy at the ceiling 3.60e+19 J. The standard geophysical account reproduces the measured behaviour of the global subduction system within the uncertainty of its inputs, and the largest correction the ceiling could contribute at terrestrial densities is far below the precision of the observations, so the measurement is consistent with the frame while also naming the threshold at which it would cease to be. A defensible ceiling matters for hazard practice, where design spectra for critical facilities depend on the largest event a fault system is asked to host; the arithmetic shows that moment magnitude ten requires a rupture geometry larger than any single mapped subduction segment, which is a statement about maps as much as about physics. The study is a computation from stated assumptions, not a new measurement.