Infrasound signals generated by production blasts in a nearby quarry

The mobile Infrasound Array ISCO of the Austrian National Data Center at GeoSphere Austria is a part of the Central and Eastern European Infrasound Network (CEEIN). It was installed early 2021 at the Trafelberg, with the premises of the Conrad Observatory in Lower Austria. In 2022 and 2023 a multitude of signals caused by production blasts of a quarry in a distance of 16 km to the array were detected at the station ISCO. Approximately 20 signals were selected, analyzed and compared not only with the data of the seismic station CONA at the Conrad Observatory but also with the recordings of the Macro Seismic Sensor Network, a local low cost sensor network. Blasting parameters were provided by the operator. In addition, video recordings for the blast process and photogrammetric surveys of the blasted rock mass are available for selected events. This data provides information about the source mechanism for the recorded infrasound signals. Analysis of waveform showed that envelopes of the investigated signals are bell-shaped. Values of peak-to-peak amplitudes range between 0.16 and 0.38 Pascal, the half widths of the envelopes vary from 1 to 3 seconds and the frequency range covers 0.25 to 6.35 Hertz. Products of the peak-to-peak amplitudes and half widths show a significant correlation (R2 = 0.6) with the total explosive charge of the blasts.

Data assessment indicates that the change of rock volume caused by the explosion generates the infrasound signal. The videos of the blasting process show an initial expansion of the blasted rock mass, followed by the deposition in front of the blasting area. We interpret the primary increase of volume and the subsequent compaction during the deposition as the source mechanism of the infrasound signal. Numerical modelling of the volume changes during the overall blasting process allows for the calculation of the infrasound source and Green’s functions.