ELSEM-Net, a network of ground-based telemetric stations for the monitoring of fracture-induced electromagnetic emissions in Greece: Instrumentation, management and analysis of recent observations associated with strong earthquakes

Abstract

The hELlenic Seismo-ElectroMagnetics Network (ELSEM-Net, http://elsem-net.uniwa.gr) is a network of telemetric stations spanning all over Greece for the monitoring of fracture-induced electromagnetic emissions (FEME), often also referred to as electromagnetic radiation (FEMR). At the laboratory scale, it has been proved that FEME/FEMR are produced by opening cracks in a wide frequency spectrum ranging from the MHz to the kHz bands as the general (macroscopic) fracture is approaching, rendering them precursors of general fracture that permit the monitoring of the gradual damage of stressed materials. FEME/FEMR is also observed at the geophysical scale, preceding strong earthquakes (EQs) with epicenters on land or near the coast-line. Based on the idea that MHz-kHz FEME/FEMR should also permit the monitoring of the gradual damage of stressed materials in the Earth’s crust, as it happens in the laboratory experiments, ELSEM-Net was gradually developed from 1992 to 1998 and currently comprises 11 stations installed in various locations in Greece. Here we present the instrumentation that has been specifically designed for ELSEM-Net, both hardware and firmware/software, as well as a web-based system for the management of the field stations, the recorded data, and the automated preliminary analysis results. Finally, we present the analysis of selected observations associated with recent strong earthquakes that hit Greece, using a most recently introduced time series analysis method. Our presentation aims to communicate in detail the experimental infrastructure behind our almost 30 years of research in geophysical scale FEME/FEMR so that other interested research groups around the world can take advantage of it and have the opportunity to install similar stations/networks in other locations of the world for the study of pre-EQ processes associated with natural or man-induced seismicity.