Preliminary catalogue of natural and anthropogenic VLF radio spectral patterns
Radio signals originating from natural and artificial (anthropogenic) sources were captured by our stationary and mobile monitoring very low frequency (VLF) radio stations. These signals were classified and divided into groups according to their source. Capturing of natural origin signals and their spectral patterns together with the time of their origin seem to confirm our assumption about the correlation between deformations in the slope and electromagnetic (EM) anomalies in the radio spectrum after further analysis. We conclude that since we always observe them a few days to hours after heavy rainfall and they are not observed at both stations at the same time, it confirms that they represent local phenomena not caused by atmospheric or ionospheric processes or events but deformation in landslide body microfracturation and microdisplacements via piezo-electromagnetic effect. Also, at the time after capture, it is possible to observe changes in the terrain in the form of new cracks of a sub-meter size. The EM field around the VLF band, DC – 30 kHz (up to 24 kHz in our measurement) was recorded using sound cards that served as an AD/DA converter. The VLF monitoring station and mobile measurements were located on the landslide slopes.