Energy-4 Generator for Monitoring Seismically Active Regions and Electromagnetic Sounding of the Earth’s Crust. Experience of Application in the Kovdor-2015 Experiment

The first section of the paper describes the developed self-powered, chassis mounted mobile Energy-4 generator, which has a power of 29 kW and a maximum output voltage of up to 1200 V. The generator operates in the audio frequency range (2–2000 Hz) and is designed for electromagnetic sounding of the Earth’s upper crust in the search for minerals and monitoring of earthquake source zones in seismically active regions. The main power units of the generator are a PWM inverter and a step-up transformer. The inverter is powered by two DC generators mounted on the driveshaft of a truck, in the body of truck of which the generator is mounted. The circuit diagram and operation of the generator are considered, as well as individual design solutions that made it possible to increase the amplitude of the output voltage and, consequently, the current in grounded power lines. The second section is devoted to full-scale tests of the Energy-4 generator in the Kovdor-2015 experiment, during which multipath frequency soundings with 25 and 50 km spacings were carried out on the territory of the Enskii–Kovdor granite-gneiss complex composed of rocks of the Archaean basement of the Baltic Shield. As a result of the experiment, a ubiquitous intermediate conducting dilatancy-diffusion layer (DD layer) was found at depths from 2–3 to 5–9 km in an area of 100 × 200 km. The parameters of this layer have been investigated. The layer is considered a seismically active element of the brittle Earth’s upper crust with a thickness of 10–15 km.