Magnetoelastic sensors and geophones for vector measurements in geoacoustics

The process of earthquake origination is associated with the action of intrinsic forces of both natural and artificial origin, which substantially change the stress fields in the Earth’s crust. These slow movements are accompanied by acoustic noise (acoustic emission). Broadband measurements of acoustic emission from naturally deposited rocks is an effective tool for an instrumental monitoring of the Earth’s crust that is aimed at earthquake forecasting. Considerable advances in this direction have become possible with the development of a new type of acoustic sensors with a velaccelerometric characteristic, for which the sensitivity increases by three orders of magnitude when the frequency increases tenfold. In geoacoustic observation systems, this makes it possible to considerably expand the amplitude-frequency range of investigation and creates new opportunities for a detailed analysis of the earthquake origination process. The results of observations of high-frequency underground acoustic noise, which were carried out in various regions of the Earth, in wells and edits, with the use of hardware/software systems containing new broadband magnetoelastic acoustic geophones, have confirmed experimentally its relation to slow deformations in the Earth’s crust. It turns out that underground hum in the frequency range from 16 to 2000 Hz contains new independent information on changes in the stressed state and is a sensitive indicator of tectonic and tidal movements. Practical investigations performed by researchers from the Institute of Volcanology, Far East Division of the Russian Academy of Sciences, in Petropavlovsk-Kamchatski have convincingly proved that acoustic noise variation may serve as a reliable seismic alert. The present publication is devoted to the history of the development and application of magnetoelastic geophones.