Update on monitoring of magnetic and electromagnetic tectonic signals in Central Italy

A Meloni A Meloni,D Di Mauro D Di Mauro,M Di Persio M Di Persio,P Palangio P Palangio,S Lepidi S Lepidi

doi:10.4401/ag-4414

A Meloni A Meloni, D Di Mauro D Di Mauro + Show 3 more

Open Access

https://doi.org/10.4401/ag-4414

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Abstract

A network of three absolute magnetometer stations and the geomagnetic observatory of LAquila (42°23N, 13°19E) monitors possible seismo- or tectonomagnetic effects in Central Italy, using LAquila Observatory as a reference for differentiation. A system of two VLF search coil wide-band antennas, working in two different frequency bands, at the LAquila Observatory, monitors possible electromagnetic effects related to seismic events occurring in Central Italy. Absolute magnetic field observations and VLF signals have been collected for several years. In particular the tectono-magnetic network started its operations in 1989. In this paper we report on the time variation of above mentioned data for the most recent years 2002 and 2003, also in connection with older measurements time series; we also report on seismic activity recorded in this area by the national seismic network. In the above mentioned time interval, no strong earthquake activity was recorded, and at the same time no clear evidence for magnetic or electromagnetic signals related to seismic events was found.

Highlights

Among various ground-based methods for monitoring the different kind of electromagnetic signals associated with the tectonic activity manifestation, like earthquakes or volcanic eruptions, the measurements of magnetic anomalies, in the frame of the so-called «tectonomagnetism», and of electromagnetic field emissions in ULF and VLF frequency bands, have been extensively used and described in recent papers (Johnston and Parrot, 1997; Meloni et al, 2001; Hayakawa and Molchanov, 2002)
Seismomagnetic and VLF data gathered in recent years were used to obtain a better knowledge of the tectonomagnetic and electromagnetic phenomena observed in this region
Data were analyzed to evaluate if results could be used in the search of possible correlation to seismic activity

Summary

Introduction

Among various ground-based methods for monitoring the different kind of electromagnetic signals associated with the tectonic activity manifestation, like earthquakes or volcanic eruptions, the measurements of magnetic anomalies, in the frame of the so-called «tectonomagnetism», and of electromagnetic field emissions in ULF and VLF frequency bands, have been extensively used and described in recent papers (Johnston and Parrot, 1997; Meloni et al, 2001; Hayakawa and Molchanov, 2002). Mechanisms for generating magnetic field changes associated with tectonic and volcanic activity are generally attributed to piezomagnetic and electrokinetic effects, assuming that rocks change their magnetization under mechanical or thermal stress and under variation of concentration gradients of electrolytes and flow of pore fluids in fractured rocks All these mechanisms are strongly supported by laboratory tests, and at present, variations of a few nT have been claimed by observers, both in the case of earthquake and volcanic events (see for example Johnston, 1997; Del Negro and Currenti, 2003). Data are differentiated with respect to the Italian magnetic observatory of L’Aquila (42°23N, 13°19E), used as a reference to eliminate non local tectonomagnetic fields on the dataset In this latter location, a system of two VLF search coil wide-band antennas, each working in two different frequency bands, monitored the electromagnetic emissions, in the search for relations to seismic events in the area. We report on seismic activity recorded in this area by the national seismic network, for the above mentioned time interval and show some tentative correlation between magnetic signals and local and regional seismic activities

The network and instrumentation

Magnetic observations

18 April 2002 20:56:00

VLF observations

Conclusions