Post-seismic Infrasounds and Tsunamis Observed by GOCE
Garcia, Raphael F.1; Bruinsma, Sean2; Lognonné, Philippe3; Doornbos, Eelco4
1IRAP OMP Université de Toulouse Paul Sabatier, FRANCE; 2CNES, Dept. of Terrestrial and Planetary Geodesy, FRANCE; 3Univ. Paris Diderot, Sorbonne Paris Cité, Institut de Physique du Globe de Paris, FRANCE; 4Faculty of Aerospace Engineering, TU Delft, NETHERLANDS
Ground displacements due to the propagation of seismic surface waves after large earthquakes generate low frequency infrasounds propagating upward in the atmosphere.
These acoustic waves are amplified and low pass filtered by the atmosphere. They create significant neutral density perturbations (>1%), and vertical wind velocities up to hundreds of m/s in the 250-350 km altitude range which have been detected previously through electron density perturbations due to neutral/plasma coupling.
We present observations of neutral density perturbations along the GOCE orbit and vertical accelerations of GOCE platform after recent large earthquakes, and demonstrate that these perturbations are due to post-seismic infrasounds. The 11% neutral density perturbations observed by GOCE, and vertical accelerations sensed by GOCE platform, when crossing the infrasonic wavefront produced by the Tohoku earthquake are reproduced with the correct waveform. Arrival times and amplitude differences are respectively smaller than 60s and a factor 2.
In addition, tsunamis propagating at the surface of the ocean generate gravity waves propagating upward in the atmosphere. We present signals observed by GOCE when crossing this tsunami generated gravity wavefront for various recent tsunamis. A first modelling of these waves reproduces the arrival time and position of the tsunami generated gravity waves observed by GOCE. Finally, these pioneering observation may influence the design of future satellite missions allowing thermospheric density retrieval, in order to constrain low frequency seismic waves in regions with poor seismometer coverage, and to validate tsunami alerts by a detection of atmospheric perturbations during their propagation in the open ocean.