Rich observations of local and regional infrasound phases made by the AlpArray seismic network after refinery explosion

Abstract

On September 1st, 2018 a devastating explosion occurred on the facility of an oil refinery near Ingolstadt, Germany. We analyzed data of 400 permanent and temporary seismic stations and find strong seismo-acoustic signals on more than 80 seismic stations. The infrasound signal is detectable on seismic stations within 10–350 km from the source, with 40 km spatial resolution. We confirm the explosion site both by the seismic and seismo-acoustic arrivals. Apart from seismic P- and S-waves, we identified three separate acoustic phases with celerities of 332, 292, and 250 m/s, respectively, each of which has a particular spatial pattern of positive detections at the ground. Seismo-acoustic amplitudes are strongly affected by the type of seismic installation but still allow insight into regional infrasound attenuation. Our observations likely represent tropospheric, stratospheric, and thermospheric phases. We performed 3D acoustic ray tracing to validate our findings. Tropospheric and thermospheric arrivals are to some extent reproduced by the atmospheric model. However, ray tracing does not predict the observed acoustic stratospheric ducts. Our findings suggest that small-scale variations had considerable impact on the propagation of infrasound generated by the explosion.

A Comprehensive Study of Infrasound Signals Detected from the Ingolstadt, Germany, Explosion of 1 September 2018

“…Of course this could be related to the rather coarse 6 h sampling of the weather prediction model of ECMWF used here. However, similar findings have been obtained by Fuchs et al (2019), who were also unable to model any stratospheric arrivals even though they found strong evidence of a stratospheric propagation branch for distances between 150 and 325 km from the Ingolstadt source. In their case they applied the same 3D ray tracing scheme as used here and an even higher-resolution ECMWF model.…”

“…We only include these data in this study, firstly, for completeness, since we used the seismic phases at GRF for event location, especially to confirm and to specify an origin time of the event, and secondly, to infer the pattern for tropospheric infrasound propagation towards the North. For seismo-acoustic arrivals at other seismic stations, namely the AlpArray network with some 400 stations within 400 km of the explosion site, we refer to Fuchs et al (2019) who investigated this data in greater detail.…”

“…The data analyses in both studies have provided a clear set of acoustic arrivals at seismic and infrasound stations throughout Central Europe. While the seismic data of the AlpArray network analysed by Fuchs et al (2019) could only be interpreted in terms of celerity based on apparent arrival time of the seismoacoustic phase, we have focused here on the infrasound array stations for which we were able to apply array processing techniques in order to obtain additional waveform parameters such as backazimuth and apparent (trace) velocity (or equivalently slowness) of the waveform signal. For the backazimuths we see a strong agreement with the theoretical values, with deviations of only a few degrees.…”

“…In this study we investigate the infrasound signals observed from the 1 September 2018 explosion on the outskirts of the city of Ingolstadt, when at the oil refinery in Vohburg a leakage in a tank generated a large cloud which ignited at 3:11:45 UTC and generated seismic and acoustic waves that were recorded at local and regional seismic sensor networks within 400 km distance of the source (Fuchs et al 2019). This ground truth information is available from the media (e.g.…”

“…The closest sensors at distances of some 15-20 km from the explosion site belong to the Gräfenberg seismic array (GRF), where not only strong seismic signals were observed but also later seismo-acoustic phases from the atmospheric waves. Fuchs et al (2019) looked at the seismic data from the temporary AlpArray network (Hetenyi et al 2018) and found, besides the corresponding seismic phases, different seismo-acoustic signal groups. They attributed these to signals that propagated in the tropospheric duct with celerities of around 332 m/s, on average, to distances of up to 200 km, in the stratospheric duct with a mean celerity of 292 m/s and observed between 150 and 325 km distance, or most likely in the thermosphere with a mean celerity of about 250 m/s identifiable at distances of 250-350 km from the source.…”