Correlation analysis technique revealing ionospheric precursors of earthquakes

Abstract

Abstract. In this paper we focus on the variability of electron concentration in the ionosphere measured by ground based ionosondes and GPS receivers around the time of strong earthquakes. It has been detected and statistically proven that several days before the seismic shock the level of this variability increases at the station closest to the epicenter, a fact which can be regarded as precursory phenomenon. More precisely the localness of this specific kind of ionospheric variability is used for the correlation analysis of data of several observation points. The similarity of geographical location of the observation points leads to the similarity of ionospheric variations registered at these sites during both quiet and disturbed geomagnetic conditions, except in the case of those located at the seismoactive zone. As a rule, the local anomalies in the F2 layer and TEC accompanying the preparation of strong earthquakes show themselves in the breaking of the mutual correlation of the critical frequencies f o F 2 or TEC between stations situated in and outside the seismic zone. The precursory phenomenon appears 1 to 7 days before the time of the seismic shock.

A qualitative study of the seismo-ionospheric precursors prior to the 6 April 2009 earthquake in L'Aquila, Italy

“…This earthquake was the main shock of a series of pre-seismic events, which started in February and continued through March 2009. The earthquake preparation area is calculated as 511 km according to the Dobrovolsky equation (Dobrovolsky et al, 1979;Pulinets et al, 2004) …”

Special case of ionospheric day-to-day variability associated with earthquake preparation

“…The similar technique for the F-layer parameters of the ionosphere was developed by Gaivoronskaya and Pulinets (2002). This technique was extended for the GPS TEC measurements (Pulinets et al, 2004a). To determine the radius of correlation associated with the seismic activity the conception of the earthquake preparation zone was used.…”

Ionospheric Precursors of Earthquakes; Recent Advances in Theory and Practical Applications

“…The daily cross-correlation coefficient (3) for the two stations should be calculated where the hourly values of the critical frequencies foF2 are used. The same technique can be used for GPS TEC records using data from two receivers selected by the same criteria as the ionospheric stations (Pulinets et al 2004b). The summation index in this case will be different depending on the GPS data sampling interval,…”