Experimental evidence of electrification processes at the 2009 LAquila earthquake mainshock

TL;DR

This study presents simultaneous observations of transient and offset magnetic field events during the 2009 LAquila earthquake, providing evidence of crustal electrification processes potentially linked to earthquake mechanics.

Contribution

It offers the first detailed analysis of local magnetic signals associated with an earthquake, challenging piezomagnetic explanations and suggesting deep crustal electrification phenomena.

Findings

Transient magnetic signals occurred during the earthquake

Offset magnetic events could not be explained by piezomagnetic effects

Signals suggest deep crustal source and are aligned with fault strike

Abstract

Two types of coseismic magnetic field events are simultaneously observed: transient offset events and magnetic field signal that occurred at the destructive, Mw6.1 LAquila earthquake (EQ) mainshock. The offset event, conventionally interpreted as a signature of piezomagnetic effects, however could not be ascribed as such. The reason is that the presently known geology of the LAquila basin consists mainly of carbonates, dolomites and limestone, thus it does not suggest an appearance of piezomagnetic related effects under EQ fracture/slip events. The second type of coseismic event, the transient magnetic signal starts simultaneously with the offset event and reaches amplitude of 0.8 nT in the total magnetic field. The signal is local one, in the sense that its form differs from the signals of ionospheric/magnetospheric origin confirmed (indirectly) by additional magnetic field data in Italy and Central Europe. The reliability of the observed local signal is examined also: it follows from the fact that the transient signal is recorded by two different measurements: i) in components (by fluxgate magnetometers) and 2) absolute one (overhauser magnetometer), it persists after the seismic wave train passage but within the first five minutes after the EQ shock and is not a consequence of ionosphere disturbances caused by the seismic wave train. Its amplitude shape resembles diffusion-like form with time scale characteristics that are indicative for a source deep in the crust. The polarity of the transient signal is in the horizontal plane and nearly parallel to the LAquila fault strike, i.e. along the NW-SE direction.