We assess two competing dynamic interpretations that have been propose
d for the short slip durations characteristic of kinematic earthquake
models derived by inversion of earthquake waveform and geodetic data.
The first interpretation would require a fault constitutive relationsh
ip in which rapid dynamic restrengthening of the fault surface occurs
after passage of the rupture front, a hypothesized mechanical behavior
that has been referred to as ''self-healing.'' The second interpretat
ion would require sufficient spatial heterogeneity of stress drop to p
ermit rapid equilibration of elastic stresses with the residual dynami
c friction level, a condition we refer to as ''geometrical constraint.
'' These interpretations imply contrasting predictions for the time de
pendence of the fault-plane shear stresses. We compare these predictio
ns with dynamic shear stress changes for the 1992 Landers (M 7.3), 199
4 Northridge (M 6.7), and 1995 Kobe (M 6.9) earthquakes. Stress change
s are computed from kinematic slip models of these earthquakes, using
a finite-difference method. For each event, static stress drop is high
ly variable spatially, with high stress-drop patches embedded in a bac
kground of low, and largely negative, stress drop. The time histories
of stress change show predominantly monotonic stress change after pass
age of the rupture front, settling to a residual level, without signif
icant evidence for dynamic restrengthening. The stress change at the r
upture front is usually gradual rather than abrupt, probably reflectin
g the limited resolution inherent in the underlying kinematic inversio
ns. On the basis of this analysis, as well as recent similar results o
btained independently for the Kobe and Morgan Hill earthquakes, we con
clude that, at the present time, the self-healing hypothesis is unnece
ssary to explain earthquake kinematics.