IMAGING EARTHQUAKES AT THE SURFACE FROM BACKPROJECTION OF IONOSPHERIC SIGNALS

Large, shallow earthquakes and tsunamis create vertical displacements at the Earth’s surface which radiate energy into the atmosphere as a pressure wave. As the pressure wave propagates through the atmosphere, it couples with the ionosphere to create a coseismic ionospheric disturbance (CID). Extensive research from the past 20 years has shown that we can detect these CIDs through a variety of methods, including global navigation space systems (GNSS). This method measures an integrated value of the total electron content (TEC) between a satellite-receiver pair.

While much work has been done to detect and model CIDs, little has been done to image the source. Backprojection is a method in seismology used to image energy released from large earthquakes. Backprojecting directly from the TEC is complicated by polarity changes during the coupling with the ionosphere as well as by the moving satellite. Here, we resolve these obstacles by inverting the TEC to obtain the atmospheric pressure wave. We show results of inversion for synthetic and real data. We then use the ionospheric TEC response associated with the 2011 Van dip-slip event (Mw 7.1) and backproject the pressure wave. We compare these acoustic back projection results to the backprojection of the raw TEC. Finally, we discuss continuing obstacles to backprojection, namely the effect of wind on travel times.