Backprojection of GNSS total-electron content signals for recent large earthquakes

Abstract:

It is well known that earthquakes and tsunamis couple energy into the dynamically fluid atmosphere. This energy can propagate up to the ionosphere where we can observe perturbations in the total-electron content (TEC) signals measured by global navigation space systems (GNSS). Recent emphasis has been placed on using these new observables to characterize earthquake and tsunami hazards from space, as well as for planetary exploration. Backprojection is an array-based imaging technique used in seismology to characterize the seismic source location, including complex energy release patterns from large earthquakes. Here we present TEC backprojection results from 3 recent earthquakes - 1) 2009 Samoa triggered doublet (Mw 8.1), 2) 2011 Van dip-slip event (Mw 7.1) and 3) 2012 Haida Gwaii strike-slip underthrust event (Mw 7.8). Each of these events presents new obstacles to overcome if backprojection is to be used routinely to monitor hazards from space. We will discuss these obstacles in detail and present approaches to overcome them. For instance, one problem arises from the fact that the observation point is non-stationary in time because the satellites are moving. Another problem stems from the relative geometry of the geomagnetic field and the incoming acoustic wave at the ionosphere. Finally, we present array-based methods to reduce artifacts in the backprojection images, e.g. array deconvolution, and we show that under favorable circumstances, this approach can be used to characterize motion at the Earth surface from space with high temporal and spatial resolution.