Case studies
Beirut explosion - August 6, 2020
A massive explosion in the city of Beirut, Lebanon, killed more than 100 people and flattened nearby buildings, sended shock waves to more than 250 kilometers across the ground. Eyewitness accounts described widespread shacking of buildings in a radius of 50 kilometers, and trembling of the ground felt still 250 kilometers away from the explosion center.
According to first estimates by geologists, the blast was equivalent to a magnitude between 3.5 - 4.5 earthquake comparable to the energy released by a detonation of 1.000 to 3.000 tons of TNT.
The explosion was not registered by the seismological stations in Hungary, but the Piszkés-tető (PSZI) infrasound stations detected the shock wave followed the explosion.
At the bottom of the following figure are the four registers of PSZI, and at the top, the detections are colored according to both apparent velocity and azimuth. In the case of a direct wave, at a distance of almost 2100 km between the Piszkés roof and Beirut - at a speed of 340 m / s - the journey time is about 1 hour 42 minutes, so the arrival is expected to be around 16:50 (UTC). Seen from PSZI, Beirut is located at an azimuth of about 134 °.
As expected, detections appeared from 134 ° +/- 4 ° at that time, shown in green at the top of the figure.
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Traces of Bolida at INFRA stations in Hungary
On the morning of February 28, 2020, around 9:30 UTC, a meteor over Croatia and Slovenia entered the atmosphere and fell to pieces with a spectacular explosion, which was also reported by many eyewitnesses from Hungary. The explosion was also registered by several seismological stations in Hungary. Based on the seismic signals, the approximate location of the explosion was also determined (Figure 1).
Figure 1. Blue dot on the map indicates the approximate location of the explosion, and seismometers have detected signs accompanying the bolida explosion at locations marked with a red dot.
Figure 2. shows the ground movements measured by nearby seismological stations on 28/02/2020 from 9:30 to 10:00 (UTC). The stations are arranged according to their distance from the specified location of the explosion (the farthest ones are below, and the farthest is about 320 km from the explosion). The seismiograms show the shock wave generated by the explosion, which coupled to the ground created a seismic wave. This is indicated by the fact that the time of appearance of the maximum of ground movements corresponds approximately to the speed of sound. The infrasound detections (PSZI2, PSZI3, PSZI4) are shown at the bottom of the figure. Infrasound detectors detect the acoustic signal directly.
Figure 2. Signs of seismometers that detected the explosion of bolida
Infrasound registrations after processing indicate that the detected signals was received just from the direction of the explosion (approximately 230 ° azimuth) (Fig. 3).
Figure 3. The infrasound detections (below) and the processed data colored according to the direction of the source (above).
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