A Comprehensive Study of Infrasound Signals Detected from the Ingolstadt, Germany, Explosion of 1 September 2018
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Pure and Applied Geophysics
A Comprehensive Study of Infrasound Signals Detected from the Ingolstadt, Germany, Explosion of 1 September 2018 KARL KOCH1
and CHRISTOPH PILGER1
Abstract—The explosion at the Ingolstadt oil refinery was widely recorded at seismic and infrasound stations deployed throughout Central Europe, to distances of several hundred to a thousand kilometres. This study focuses on the wealth of data recorded at infrasound stations in Central and Eastern Europe, while from the many detecting seismic stations within 400 km range, only seismic and seismo-acoustic arrivals at the close-in Gra¨fenberg array are considered here. Most of the infrasound stations are acoustic arrays enabling us to apply array processing techniques to determine relevant wave field parameters, such as backazimuth and slowness (resp. trace velocity). These parameters not only confirm the source direction, but also put constraints on the observed arrivals’ propagation modes. Wave field parameters suggest that we observe tropospheric arrivals to about 150 km and stratospheric and/or thermospheric returns for longer distances. 1D, 2D and 3D ray tracing predict tropospheric arrivals to westerly directions up to distances of 100 km, beyond which only thermospheric returns are obtained azimuth-independent beyond 250–300 km. Stratospheric returns do not follow from any of the increasingly complex ray tracing models. Parabolic equation propagation modeling however suggests that in a number of cases stratospheric ducting may be possible. However, neither the tropospheric seismo-acoustic arrivals at the Gra¨fenberg array nor the various arrivals at IMS station IS26 could be modeled. Therefore, the Ingolstadt explosion along with the observed infrasonic phases provide an excellent test bed to investigate our ability in realistically forecasting atmospheric wave propagation with existing algorithms and available atmospheric models. Keywords: Infrasound, explosion, atmospheric propagation modeling, stratospheric ducting.
models,
1. Introduction Probing the atmosphere by the propagation of infrasound signals has now become an important scientific field with the advent of the Comprehensive
1 Federal Institute for Geosciences and Natural Resources, Stilleweg 2, 30655 Hannover, Germany. E-mail: karl. [email protected]; [email protected]
Nuclear-Test-Ban Treaty. There, a network of infrasound sensors within the International Monitoring System (IMS) is surveilling the globe for atmospheric pressure disturbances that could originate from nuclear testing, especially in the atmosphere, and thus would constitute a violation of this treaty. As this infrasound sensor network is sparse and one primary objective within the verification tasks for the Treaty is the accurate location of such a source, an accurate model of atmospheric propagation conditions is required. Only this can ensure the precise interpretation of the observed signals from the associated atmospheric waves, which can travel closely along the Earth’s surface within the tropospheric
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