GPS observations of postseismic deformation for the 1995 Hyogo-ken Nanbu earthquake, Japan

11-months of GPS observations, which started within 2 days of the 1995 Hyogo-ken Nanbu earthquake, detected significant postseismic crustal deformation that reached 20 mm at some stations. A comparison of postseismic and coseismic deformation shows a similar pattern in the direction of displacements. We tried to determine the predominant relaxation mechanism by examining the time dependence of observed postseismic deformation. We considered three models: an exponential, a power-law, and a logarithmicaly decaying model. However, each of these three time-dependent models can explain the observed data, equally well. In case of the exponential relaxation model, the relaxation time constant was estimated to be about 50 days. In the power-law model, the index p was nearly 1.0; this is almost the same as the p value of Omori's decay law of aftershock sequences for this event. This suggests that the mechanism causing postseismic deformation may be related to that producing aftershocks.