Bayesian Estimation of 2005 Fukuoka (Japan) Earthquake Source Parameters and Associated Coulomb Failure Stress Changes from InSAR and GPS

Abstract:

A shallow magnitude 6.6 strike-slip earthquake occurred offshore west of the Fukuoka prefecture, Northern Kyushu Island in Japan in 2005. We use InSAR stable point-target data and GPS to constrain the location and source parameters of the mainshock. We use a uniform slip model on a rectangular dislocation in a homogenous elastic half-space and implement Bayesian estimation to obtain uncertainties for the derived model parameters. The offshore location of the earthquake makes the fault parameter estimation challenging, as the geodetic data only cover the area to the east of the earthquake. The marginal distributions of the source parameters show that the location of the western end of the fault is poorly constrained by the data whereas the eastern end, located closer to the shore, is better resolved. We use Gaussian a priori constraint on the moment magnitude (Mw 6.6) and the location of the fault with respect to the aftershock distribution of the earthquake and find the amount of fault slip to be in the range from 1 m to 1.3m with decreasing probability. We propagate the fault model uncertainties and calculate the variability of Coulomb Failure stress changes for the Kego fault, located directly below Fukuoka city, showing that the mainshock increased stress on the fault and brought it closer to failure, a concern for the Fukuoka city authorities and inhabitants.