Pierrick Mialle

A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors

Most large (over a kilometre in diameter) near-Earth asteroids are now known, but recognition that airbursts (or fireballs resulting from nuclear-weapon-sized detonations of meteoroids in the atmosphere) have the potential to do greater damage than previously thought has shifted an increasing portion of the residual impact risk (the risk of impact from an unknown object) to smaller objects. Above the threshold size of impactor at which the atmosphere absorbs sufficient energy to prevent a ground impact, most of the damage is thought to be caused by the airburst shock wave, but owing to lack of observations this is uncertain. Here we report an analysis of the damage from the airburst of an asteroid about 19 metres (17 to 20 metres) in diameter southeast of Chelyabinsk, Russia, on 15 February 2013, estimated to have an energy equivalent of approximately 500 (±100) kilotons of trinitrotoluene (TNT, where 1 kiloton of TNT = 4.185×1012 joules). We show that a widely referenced technique of estimating airburst damage does not reproduce the observations, and that the mathematical relations based on the effects of nuclear weapons—almost always used with this technique—overestimate blast damage. This suggests that earlier damage estimates near the threshold impactor size are too high. We performed a global survey of airbursts of a kiloton or more (including Chelyabinsk), and find that the number of impactors with diameters of tens of metres may be an order of magnitude higher than estimates based on other techniques. This suggests a non-equilibrium (if the population were in a long-term collisional steady state the size-frequency distribution would either follow a single power law or there must be a size-dependent bias in other surveys) in the near-Earth asteroid population for objects 10 to 50 metres in diameter, and shifts more of the residual impact risk to these sizes.

Monitoring the Earth’s Atmosphere with the Global IMS Infrasound Network

The comprehensive nuclear-test-ban treaty organization (CTBTO) is tasked with monitoring compliance with the comprehensive nuclear-test-ban treaty (CTBT), which bans nuclear weapon explosions underground, in the oceans, and in the atmosphere. The verification regime includes a globally distributed network of seismic, hydroacoustic, infrasound, and radionuclide stations, which collect and transmit data to the International Data Centre (IDC) in Vienna, Austria, shortly after the data are recorded at each station. The infrasound network defined in the protocol of the CTBT comprises 60 infrasound array stations. Each array is built according to the same technical specifications; it is typically composed of 4–9 sensors, with 1–3 km aperture geometry. This constitutes the first global infrasound network ever built with such a large and uniform distribution of stations.

On the use of remote infrasound and seismic stations to constrain the eruptive sequence and intensity for the 2014 Kelud eruption

The February 2014 eruption of Kelud volcano (Indonesia) destroyed most of the instruments near it. We use remote seismic and infrasound sensors to reconstruct the eruptive sequence. The first explosions were relatively weak seismic and infrasound events. A major stratospheric ash injection occurred a few minutes later and produced long-lasting atmospheric and ground-coupled acoustic waves that were detected as far as 11,000 km by infrasound sensors and up to 2300 km away on seismometers. A seismic event followed similar to 12 minutes later and was recorded 7000 km away by seismometers. We estimate a volcanic intensity around 10.9, placing the 2014 Kelud eruption between the 1980 Mount St. Helens and 1991 Pinatubo eruptions intensities. We demonstrate how remote infrasound and seismic sensors are critical for the early detection of volcanic explosions, and how they can help to constrain and understand eruptive sequences.

CTBT infrasound network performance to detect the 2013 Russian fireball event

The explosive fragmentation of the 2013 Chelyabinsk meteorite generated a large airburst with an equivalent yield of 500 kT TNT. It is the most energetic event recorded by the infrasound component of the Comprehensive Nuclear-Test-Ban Treaty-International Monitoring System (CTBT-IMS), globally detected by 20 out of 42 operational stations. This study performs a station-by-station estimation of the IMS detection capability to explain infrasound detections and nondetections from short to long distances, using the Chelyabinsk meteorite as global reference event. Investigated parameters influencing the detection capability are the directivity of the line source signal, the ducting of acoustic energy, and the individual noise conditions at each station. Findings include a clear detection preference for stations perpendicular to the meteorite trajectory, even over large distances. Only a weak influence of stratospheric ducting is observed for this low-frequency case. Furthermore, a strong dependence on the diurnal variability of background noise levels at each station is observed, favoring nocturnal detections.

Infrasound and seismic detections associated with the 7 September 2015 Bangkok fireball

A bright fireball was reported at 01:43:35 UTC on September 7, 2015 at a height of

Advances in Operational Processing at the International Data Centre

\sim

Bayesian association of multiple infrasound events using long-range propagation models

∼30 km above 14.5