Electromagnetic field observations by the DEMETER satellite in connection with the 2009 L'Aquila earthquake

Igor Bertello,Maurizio Candidi,Mirko Piersanti,Piero Diego,Pietro Ubertini

doi:10.5194/angeo-36-1483-2018

Abstract

Abstract. To define a background in the electromagnetic emissions above seismic regions, it is necessary to define the statistical distribution of the wave energy in the absence of seismic activity and any other anomalous input (e.g. solar forcing). This paper presents a completely new method to determine both the environmental and instrumental backgrounds applied to the entire DEMETER satellite electric and magnetic field data over L'Aquila. Our technique is based on a new data analysis tool called ALIF (adaptive local iterative filtering, Cicone et al., 2016; Cicone and Zhou, 2017; Piersanti et al., 2017b). To evaluate the instrumental background, we performed a multiscale statistical analysis in which the instantaneous relative energy (ϵrel), kurtosis, and Shannon entropy were calculated. To estimate the environmental background, a map, divided into 1∘×1∘ latitude–longitude cells, of the averaged relative energy (ϵrel‾), has been constructed, taking into account the geomagnetic activity conditions, the presence of seismic activity, and the local time sector of the satellite orbit. Any distinct signal different (over a certain threshold) from both the instrumental and environmental backgrounds will be considered as a case event to be investigated. Interestingly, on 4 April 2009, when DEMETER flew exactly over L'Aquila at UT = 20:29, an anomalous signal was observed at 333 Hz on both the electric and magnetic field data, whose characteristics seem to be related to pre-seismic activity.

Highlights

The nature of the Earth’s interior, in terms of the dynamics of the crust, mantle, and core, can be investigated through extended ground-based and space observations (Bell, 1982; Hayakawa and Molchanov, 2002; Pulinets and Boyarchuk, 2004; De Santis et al, 2015)
Taking into account that extreme reliability is needed to call for preseismic phenomena, a characteristic background for the regions on Earth where we want to detect the effects of earthquake-related electromagnetic emissions (EMEs) should be available
The correct identification of a background in the e.m. emission over seismic regions has a crucial role for the detection of possible signals related to earthquake or pre-earthquake activity

Summary

Introduction

The nature of the Earth’s interior, in terms of the dynamics of the crust, mantle, and core, can be investigated through extended ground-based and space observations (Bell, 1982; Hayakawa and Molchanov, 2002; Pulinets and Boyarchuk, 2004; De Santis et al, 2015). Comprehensive study of both magnetospheric and ionospheric disturbances driven by ground preseismic EME waves has to be carried out In this context, aseismic fault creep and EME waves are expected to be the principal mechanical and electromagnetic earthquake precursors, respectively (Buzzi, 2007, and references therein). Nemec et al (2008) built a statistical map of electromagnetic wave intensity obtained from DEMETER satellite ICE and IMSC data available at that time (2004–2007) They estimated the probability of occurrence during a seismic event of signals with higher intensity with respect to the background level defined by the map.

DEMETER data

Instrumental background

Environmental background

Discussion and conclusions