Geodetic measurements made after the 1964 Niigata, Japan, earthquake (M = 7.5) show that a broad region both in and around the aftershock zone subsided at a rate which decreased nearly exponentially for a year following the earthquake. This is inferred to be a result of recovery of dilatancy which is believed to have preceded the earthquake. Analysis using one-dimensional consolidation theory agrees well with this interpretation and indicates that the dilatant zone was a layer approximately 10 km thick with a diffusivity of approximately 104 cm2/sec and a lateral extent of at least 50 km.
Measurements made after the 1946 Nankaido, 1923 Kanto, and 1964 Alaska earthquakes suggest that they too were followed by dilatancy recovery. These observation provide further considerable information regarding this phenomenon can be obtained from post-earthquake observations.