When an earthquake ruptures a fault at depth, the displacement at the surface is usually less. Deep rock moves meters; the surface moves less. This difference — the shallow slip deficit — has been observed so consistently across decades of earthquake records that it became built into seismic hazard models. The models predict that surface shaking near major faults will be somewhat attenuated relative to the energy released at depth. Building codes and infrastructure planning in fault-adjacent areas incorporate this discount.
On March 28, 2025, a magnitude 7.8 earthquake ruptured 480 kilometers of the Sagaing Fault in Myanmar. The rupture propagated faster than seismic shear waves — a rare supershear event. But the structural surprise wasn't the speed. It was what happened at the surface. The massive slip that occurred kilometers underground transferred one hundred percent to the surface. The shallow slip deficit was zero. No discount. No attenuation. Every meter of deep displacement became a meter of surface rupture.
The deficit was never a physical law. It was an empirical regularity — an observation that happened to hold across a particular set of historical earthquakes in a particular set of geological contexts. The Sagaing Fault's straight geometry, smooth interface, and 186 years of accumulated stress since its last major event in 1839 produced conditions where the deficit vanished.
Hazard models calibrated against the regularity are wrong precisely when it matters most. The discount appears in moderate earthquakes on complex faults. It disappears in catastrophic earthquakes on simple ones — the class of events that produces the most damage. The safety margin existed in the data but not in the physics. The exception proved more dangerous than the models predicted, because the models were built from the rule.