Could the moderate-sized earthquakes trigger pre-seismic ionospheric irregularities? Study of the 2011 Murcia earthquake in the Mediterranean region (SE-Spain).

The interest of this research work is focused on the detection of possible pre-seismic perturbations related to medium-sized earthquakes (5≤Mw≤5.9) occurring in the upper ionized atmosphere (about 350 km above the Earth, ionospheric F2-region). For this specific purpose, we have exploited several geodetic data, derived through signal processing of dual-frequency permanent ground-based Global Positioning System (GPS)/Global Navigation Satellite Systems (GNSS) receivers, located at the Euro-Mediterranean basin.

To find out whether the ionospheric F2-layer is responsive to the energy released during the preparation periods of medium magnitude earthquakes, the Lorca seismic event (May 11^th, 2011, Mw 5.1, Murcia region) was taken as an initial sample. For this shallow-focus earthquake (4 km depth), the longitude-latitude coordinates of the epicenter are 1.7114° W, 37.7175° N. As result, modeling regional ionosphere using GPS/GNSS-total electron content (TEC) measurements over the epicentral area through spherical harmonic analysis, allowing us to identify pre-earthquake ionospheric irregularities in response to the M5.1 Lorca event. After discerning the seismo-ionospheric precursors from those caused by space weather effects, via wavelet-based spectral analysis, these irregularities were identified about a week before the onset of the mainshock.

The seismo-geodetic technique adopted in this study validates our hypothesis that stimulates the existence of a strong correlation between deep lithospheric deformations and pre-seismic ionospheric anomalies due to moderate magnitudes.

Keywords: Murcia earthquake, Seismo-ionospheric precursors, Spherical harmonic analysis, Wavelet transform, GPS/GNSS-TEC, Lithospheric deformations, Regional F2-ionosphere maps.