Blast in French explosives factory, Billy-Berclau
Läslo Evers
A blast occurred in an explosives factory in France, Billy-Berclau
on 2003, March 27. The blast took place at approximately 6h15 local time
(5h15 GMT), see also
BBC news.
Infrasound of the blasts was detected to the Northeast at the De Bilt
Infrasound Array, DBN. The energy
showed up as coherent infrasound, see Figure 1.
Figure 1: The recording at the microbarometers in DBN, the horizontal
axis gives time in seconds and the vertical axis shows air pressure in
pascals (Pa). The time axis
zero time is 2003, March 27 06h22m51.06s local time (GMT+1h). The first coherent
energy arrives after 254 seconds thus at 6h27m05s.
The data are bandpass filtered with corner frequencies of 0.5 and
15 Hz.
The data at analyzed on the basis of the Fisher ratio, evaluated in the
time domain. An increase in Fisher ratio corresponds to a coherent infrasound
wave having travelled over the array. Figure 3 shows the results of this
analysis for the infrasound data in DBN.
Figure 2: Analysis of the infrasound data. The increase in Fisher ratio,
in the lower frame, corresponds to the coherent infrasound of the blast.
Event characteristics of 342.7 m/s and 218.4 degrees are found at the maximum
Fisher ratio.
Energy of the explosion was also recorded at infrasound arrays in France and
Germany. Figure 3 gives the location found by cross bearing of the resolved
back azimuths. The location found is slightly different from the true
location (blue triangle). Especially strong winter stratospheric directed
towards the East will affect the transverse paths of infrasound.
Figure 3: Cross bearing of the resolved back azimuths in DBN, Flers (France) and
IS26 (Germany). The back azimuths are not corrected for the wind.
The contributions of Alexis le Pichon from the Commissariat à l'Energie Atomique, France, and Gernot Hartmann from Bundesanstalt f. Geowissenschaften u. Rohstoffe, Germany, are acknowledged.
March 2003
Läslo Evers