A Comparative Study of Geoelectric Signals Possibly Associated with the Occurrence of Two M(s) > 7 EQs in the South Pacific Coast of Mexico

During past decades, several studies have suggested the existence of possible seismic electric precursors associated with earthquakes of magnitude [Formula: see text]. However, additional analyses are needed to have more reliable evidence of pattern behavior prior to the occurrence of a big event. In this article we report analyses of self-potential [Formula: see text] records during approximately two years in three electro-seismic stations in Mexico located at Acapulco, Guerrero; Petatlán, Guerrero and Pinotepa Nacional, Oaxaca. On 18 April 2014 an [Formula: see text] earthquake occurred near our Petatlán station. Our study shows two notable anomalies observed in the behavior of the Fourier power spectrum of [Formula: see text] for ultra low frequency ULF-range, and the transition of the [Formula: see text]-exponent of the detrended fluctuation analysis of the [Formula: see text] time series from uncorrelated to correlated signals. These anomalies lasted approximately three and a half months before the main shock. We compare this electric pattern with another electric signal we reported associated with an [Formula: see text] that occurred on 14 September 1995 at Guerrero state, Mexico. Our characterization of the anomalies observed in both signals point out similar features that enrich our knowledge about precursory phenomena linked to the occurrence of earthquakes of magnitude [Formula: see text].