Data assimilation of the earth´s atmospheric and ionospheric oscillations excited by large earthquakes

Evidence of large earthquakes is sometimes recorded by non-seismic geophysical sensors such as those used for crustal, atmospheric, and/or electromagnetic observations. When the 2008 Iwate-Miyagi Nairiku Earthquake and the 2011 Great East Japan Earthquake occurred near Japan, microbarometers and electromagnetic antennas, which are located >;400 km from the epicenter, detected air pressure and Doppler shift variations, respectively. These observations indicate that coseismic acoustic waves, i.e., the sounds of the earthquakes, were launched from the faults and propagated in the atmosphere, including the ionosphere. A normal mode summation, together with data assimilation, which is a fundamental technique for combining numerical simulations and observation data, reproduces the observed coseismic waveforms assuming realistic source mechanisms in a one-dimensional model of the Earth´s structure that consists of the solid Earth and the atmosphere. The synthetic waveforms reproduced from maximum-a-posteriori solutions of the seismic parameters successfully account for the observed waveforms with a slight change in the altitude of the ionosphere from the observation, which indicates that the proposed data assimilation procedure provided strong feedback for updating the observations and/or the simulation models.