Fault parameter estimation with data assimilation on infrasound variations due to big earthquakes

A procedure to estimate, in the framework of data assimilation, fault parameters from excited infrasound phenomena due to big earthquakes is proposed. Seismoacousic waves generated by several point sources are simulated by the convolution of the relevant seismic source mechanism and the Green´s function constructed from normal modes of an assumed Earth´s model. Unknown parameters in a rupturing fault model are estimated in order to explain real observed infrasound variations in detail. As an example, the proposed procedure is applied to infrasound variations associated with the Iwate-Miyagi Nairiku Earthquake that occurred in northeast Japan in June 2008. Coseismic infrasound variations are numerically simulated using an appropriate fault model and a one-dimensional coupled structure model consisting of the solid Earth and the atmosphere. Fault parameters, such as rupture velocity and scalar seismic moment, are determined using the particle filter algorithm to fit the long-period components of the observed infrasound variations. The posterior distribution obtained for each fault parameter indicates that infrasound data contain sufficient information as well as seismic data.