Determining the parameters of ionospheric perturbation caused by earthquakes using the quasi-optimum algorithm of spatiotemporal processing of TEC measurements

Abstract

We present the quasi-optimum algorithm of localization of a source of coseismic ionospheric perturbation based on GPS receivers’ network data processing. The initial data of the algorithm are the series of variations of ionospheric total electron content (TEC), reconstructed using the measurements of the phase delays of GPS signals. In order to select the TEC increments caused by ionospheric perturbation due to the earthquake, the TEC series are filtered using a special procedure. The algorithm realizes coherent summation of all TEC series of GPS array reasoning from the maximization of the energy of the total signal of the ionospheric response to earthquake. The quasi-optimum algorithm allows determination of the perturbation propagation velocity as well as of the coordinates, height and “switch-on” time of a source of coseismic ionospheric disturbance without prior information about the perturbation form and the site and time of the main shock of earthquake. We used the algorithm for measuring the parameters of ionospheric perturbations which accompanied the earthquake in the vicinity of Hokkaido Island on September 25, 2003 and the earthquake near the south coast of Honshu Island on September 5, 2004. The results of these experiments show the high accuracy of the perturbation source coordinates estimation (33 km and 27 km respectively with reference of the earthquakes epicenters). The estimations of perturbations propagation velocity (820 ± 60 m/s and 460 ± 40 m/s), heights (340 ± 80 km and 370 ± 130 km) and “switch-on” delay (346 s and 507 s) of a source of the perturbation obtained in both experiments are in agreement with a theory according to which coseismic atmospheric disturbance propagates within a narrow cone of zenith angles up to ionospheric heights and then diverges in the form of a spherical wave with the radial velocity close to the speed of sound at these heights. It is also in agreement with the results of earlier researches.