The 12 December 2017 Baumgarten Gas Hub Explosion: A Case Study on Understanding the Occurrence of a Large Infrasound Azimuth Residual and a Lack of Seismic Observations

Koch, Karl ORCIDiD
Pilger, Christoph ORCIDiD
Czanik, Csenge
Bondár, István

DOI: https://doi.org/10.1007/s00024-020-02549-2
Persistent URL: http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/11225
Koch, Karl; Pilger, Christoph; Czanik, Csenge; Bondár, István, 2020: The 12 December 2017 Baumgarten Gas Hub Explosion: A Case Study on Understanding the Occurrence of a Large Infrasound Azimuth Residual and a Lack of Seismic Observations. In: Pure and Applied Geophysics, 177, 10, 4957-4970, DOI: https://doi.org/10.1007/s00024-020-02549-2. 
 
Koch, Karl; BGR Hannover, Federal Institute for Geosciences and Natural Resources, Hannover, Germany
Pilger, Christoph; BGR Hannover, Federal Institute for Geosciences and Natural Resources, Hannover, Germany
Czanik, Csenge; CSFK, Budapest, Research Centre for Astronomy and Earth Sciences, Geodetic and Geophysical Institute, Kövesligethy Radó Seismological Observatory, Budapest, Hungary
Bondár, István; CSFK, Budapest, Research Centre for Astronomy and Earth Sciences, Geodetic and Geophysical Institute, Kövesligethy Radó Seismological Observatory, Budapest, Hungary

Abstract

The Baumgarten explosion occurred on 12 December 2017 at a gas storage site about 30 km east of Vienna, Austria. Acoustic arrivals from this accidental surface explosion were detected at dozens of stations of the AlpArray seismic network to distances up to 150 km, mainly in easterly directions. Thus it was expected that the Hungarian infrasound array PSZI located about 230 km to the east-southeast of Baumgarten would detect this acoustic wave as well. Standard progressive multichannel correlation processing and frequency-wavenumber analysis identified a signal emerging at 7:57:55 UTC from an azimuth of 296°–300° and with trace-velocity > 400 m/s. The extraordinarily high trace-velocity and excessive backazimuth residual, relative to the explosion site direction of 282°, however cast strong doubts on the arrival’s connection to the Baumgarten event. Accounting for the effect of non-planar geometry of the infrasound array results in a reduction of the azimuth residual by half. Additionally, 2D and 3D raytracing methods are used including the European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric model to further explain the remaining azimuth residual as well as to elucidate the large trace velocity estimates. The prevailing stratospheric winds in excess of 150 m/s are identified as the underlying cause. Including both factors the initial azimuth residual of up to 18° decreases to ~ 4°, allowing to associate the infrasound signal at PSZI with the Baumgarten event. Finally, the data from a seismic station at 30 km range is re-investigated for magnitude estimation. The local magnitude of ML < 1.0 explains well the scarcity of seismic observations within 50 km range, where three or four stations show signals, mainly consisting of Rg-type surface waves, but no body waves.