Ionospheric evidence of the May 1960 earthquake over Concepción

For many years relations between seismic activity and associated ionospheric changes have been studied. Particularly, the possibility to identify ionospheric precursors of large earthquakes has been regarded as a specific goal for eventual obvious very valuable practical use. This paper first analyses foF2 observations over Concepcion (36.8°S; 73.0°W) prior to the two very large Chile earthquakes of 21 and 22 May 1960, using the same procedure of Chuo et al. (2002) for the September 1999 Taiwan earthquake. Then it reports results from processing foF2 values in two different ways, namely, using direct estimations of reference geomagnetic quiet-day diurnal variation of foF2 and using an empirical model that filters known dependencies of foF2 on solar and geomagnetic activities for Concepcion (Arriagada and Foppiano, 1999). It is shown that different analyses of observed foF2 values lead to different conclusions regarding possible ionospheric precursors.