Infrasonic Stations Research Articles

Infrasound associated with the eruption of the Hunga volcano.

On 13-15 January 2022, the Hunga Tonga-Hunga Ha'apai underwater volcano erupted. This powerful eruption generated infrasonic waves with amplitudes of thousands of Pascals in the near field. The ground infrasonic stations in China, located approximately 10 000 km from the Hunga volcano, also received waves with frequencies from 0.01 to 0.05 Hz. However, the amplitude reached 17 Pa, which is higher than the predicted amplitude using the absorption model without considering the dispersion effect in the thin thermosphere. At high altitudes, dispersion exists and the sound speed depends on the ratio of the molecular mean collision ratio to sound frequency, which is proportional to the ratio (frequency/pressure). And attenuation coefficients are complex to model. We simulate dispersive sound speeds and attenuation coefficients at different frequencies according to theory and our experimental data. In the thermosphere, the dispersion effect causes noticeable changes of sound speed and then affects wave propagation paths in the far field. The abnormal attenuation coefficient has a smaller impact on thermospheric returns than that of the dispersive sound speed, but it is also not negligible. It explains the large amplitude of thermospheric signals received in our infrasound stations. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

Measurement and characterization of infrasound waves from the March 25, 2023 thunderstorm at the near equatorial

<abstract> <p>Thunderstorm activity on March 25, 2023 provided a unique opportunity to study the mechanism of lightning events on changes in air pressure. In particular, this event made it possible to study changes in air pressure during thunderstorms using various instruments. This paper presented comprehensive results of infrasound, satellite data, weather radar and weather measurements at the ground during the storm. Observations of lightning events were confirmed using observational data from the International Space Station's Lightning Imaging Sensor (ISS LIS). This work estimated three spectral percentile values on infrasonic sensor data, time series interpolation of standard meteorology profiles, weather radar reflectivity and total radiant energy of lightning from ISS LIS observations during the day and night periods. As a result, during the investigation, it was seen that the recorded infrasound signal in the 0.6–0.8 Hertz (Hz) range was contaminated by background environmental noise, but in the 1–3 Hz band range it was consistent with the appearance of storms that produce high energy blows. Infrasound detection and electromagnetic lightning detection show good correlation up to a distance of 100 km from the infrasonic station. During a thunderstorm, the ISS LIS flight directly above the observation site detected more than 2,000 lightning events. In addition, the application of lightning detection from several independent instruments can provide a complete picture of the observed event.</p> </abstract>

Remote Seismoacoustic Constraints on the January 2022 VEI 4 Eruption in Tonga

AbstractThe major eruption that occurred on 15 January 2022 on Hunga Tonga Hunga Ha’apai (HTHH) in Tonga generated powerful acoustic waves that propagated through the atmosphere all over the world. Although the eruption energy was soon estimated from the acoustic waves and the ash cloud, its ranking on the Volcanic Explosivity Index (VEI) is still debated. Here, we show the erupted magma volume can be calculated from the significant resonance of the remote seismoacoustic waves recorded in Taiwan. A resonant frequency (f) of ∼0.0117 Hz persisted for >25 min was clearly recorded by both a dense broadband seismic array and also several infrasonic stations in Taiwan. If the volcanic cavity produced by the erupting magma is considered a classic Helmholtz resonator, then the f constrains the possible volume of the erupted magma to 0.215±0.015 km3. We may conclude that the major eruption on HTHH rated a 4 on the VEI scale. In addition to neutralization between low content of the sulfur dioxide and a huge amount of water, it is potentially too small to cause any significant climate change in 2022.

Performance Assessment of Geophysical Instrumentation Through the Automated Analysis of Power Spectral Density Estimates

AbstractThis study describes an automated data quality verification procedure supported by a database of power spectral densities (PSD) estimates for geophysical waveform data. The Royal Netherlands Meteorological Institute (KNMI) manages a 100‐TB archive of continuous geophysical data collected from accelerometers, geophones, broadband seismometers, and infrasonic arrays deployed across the continental and Caribbean Netherlands. This rapidly expanding network at a scale of over 700 instruments makes the manual evaluation of data quality impractical and must be supported by data policies and automated methods. A technique is presented to compress and store PSD estimates in a database with a storage footprint of less than 0.05% of the raw data archive. Every week, the instrument performance is validated by comparing statistical properties of its latest monthly probabilistic PSD distribution to strict quality metrics. The criteria include thresholds based on global noise models, datalogger quantization noise models, constraints imposed by ambient noise conditions, and confidence intervals based on PSD estimates calculated from validated archived data. When a threshold is crossed, the station operator is alerted of the suspected degraded instrument performance, severely limiting the required amount of manual labor and associated human errors. The automated PSD assessment technique is applicable to accelerometers, geophones, broadband seismometers, infrasonic stations, and is demonstrated to be extendable to hydrophones, gravimeters, tiltmeters, and Global Navigation Satellite System receivers. The approach is therefore suitable for other geophysical monitoring infrastructures, for example, observational networks dedicated to continuous volcano monitoring. It is shown that it possible to detect degraded instrument performance that may otherwise remain undetected.

Remote hydroacoustic-infrasonic detection and characterization of Anak Krakatau eruptive activity leading to, during, and following the December 2018 flank collapse and tsunami

A climactic eruption phase on December 22, 2018, triggered the collapse of the southwest flank and summit of Anak Krakatau stratovolcano, generating a tsunami which struck the coastlines of Sumatra and Java. We employ a selection of remote moored hydroacoustic (H08S, 3307 km; H01W, 3720 km) and infrasonic (IS06, 1156 km; IS07, 3475 km; IS52, 3638 km) stations of the International Monitoring System (IMS) to investigate eruptive activity preceding, during, and after the climactic eruption phase. We observe 6 months of co-eruptive intermittent infrasound at IS06 and powerful infrasound from the climactic eruption on IS06 and IS52. The climactic eruption phase was not detected hydroacoustically, but we observe a ~ 12-day swarm of hydroacoustic signals beginning 24 days before the flank collapse event that we attribute to sustained submarine eruptive activity at Anak Krakatau. We perform hydroacoustic waveform and envelope multiplet analysis to assess event similarity during the hydroacoustic swarm. Hydroacoustic waveforms are not well-correlated, but envelopes with a main pulse duration of ~ 20-s are correlated, with 88.7% of 247 events grouping into two multiplets using a threshold correlation coefficient of 0.75. The repetitive envelopes indicate a repetitive impulsive volcanic process, either underwater submarine explosions or volcanic earthquakes in the solid Earth coupled to the water column from the Sunda Shelf. This study further underscores the potential of remote acoustic technology for detecting and characterizing eruptions at submarine or partially submerged volcanoes.

Identification of infrasonic and seismic components of tremors in single-station records: application to the 2013 and 2018 events at Ioto Island, Japan

Infrasonic stations are sparse at many volcanoes, especially those on remote islands and those with less frequent eruptions. When only a single infrasound station is available, the seismic–infrasonic cross-correlation method has been used to extract infrasound from wind noise. However, it does not work with intense seismicity and sometimes mistakes ground-to-atmosphere signals as infrasound. This paper proposes a complementary method to identify the seismic component and the infrasonic component using a single microphone and a seismometer. We applied the method to estimate the surface activity on Ioto Island. We focused on volcanic tremors during the phreatic eruption on April 11, 2013, and during an unconfirmed event on September 12, 2018. We used the spectral amplitude ratios of the vertical ground motion to the pressure oscillation and compared those for the tremors with those for known signals generated by volcano-tectonic earthquakes and airplanes flying over the station. We were able to identify the infrasound component in the part of the seismic tremor with the 2013 eruption. On the other hand, the tremor with the unconfirmed 2018 event was accompanied by no apparent infrasound. We interpreted the results that the infrasound with the 2013 event was excited by the vent opening or the ejection of ballistic rocks, and the 2018 event was not an explosive eruption either on the ground or in the shallow water. If there was any gas (and ash) emission, it might have occurred gently undersea. As the method uses the relative values of on-site records instead of the absolute values, it is available even if the instrument sensitivity and the station site effects are poorly calibrated.

Parameters of the infrasonic signal generated by the Kamchatka meteoroid

The subject of this study is the infrasonic signal generated by a high-speed (32 km/s), high-energy (173 kt TNT), and large-sized (9.4 m) celestial body, later called the Kamchatka meteoroid, which entered the terrestrial atmosphere and exploded on December 18, 2018. The focus of the study is the parameters of the infrasonic signal launched by the Kamchatka meteoroid. The study is based on the data on temporal dependences of pressure in the infrasonic wave collected by the I53US, I30JP, I59US, I46RU, I57US, and MAAG2 infrasonic stations included in the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The measurement data initially recorded on a relative scale were converted into absolute values. The temporal dependences of the infrasonic wave pressure were then filtered in the 1–40-s period range and were subsequently subjected to system spectral analysis that included the mutually complementary short-time Fourier transform, adaptive Fourier transform, and the wavelet transform with the Morlet wavelet as the basis function. As a result, it was found that the infrasonic signal amplitude exhibits quite a rapid decrease with distance between an infrasonic station and the meteoroid’s explosion site. The time delay of the infrasonic signal shows an increase with distance between the celestial body explosion and the site of signal detection. The signal celerity exhibits a dependence on the distance and the path orientation; it is estimated to be in the range of 269–308 m/s. The infrasonic signal duration shows virtually no dependence on the distance from the detonation point to an infrasonic station. The infrasonic signal spectra have a wide bandwidth with periods from ∼5 to ∼40 s. At the same time, the greatest energy falls within the isolated periods of 12–15 s and 28–33 s. The scatter diagrams and regressions for the infrasound main parameters were plotted. The celestial body’s kinetic energy (179 kt TNT) and acoustic efficiency (∼4%) were estimated from the prevailing infrasonic period.

Parameters of the Infrasonic Signal Generated by the Kamchatka Meteoroid

The subject of this study is the infrasonic signal generated by a high-speed (32 km/s), high-energy (173 kt TNT), and large-sized (9.4 m) celestial body, later called the Kamchatka meteoroid, which entered the terrestrial atmosphere and exploded on December 18, 2018. The focus of the study is the parameters of the infrasonic signal launched by the Kamchatka meteoroid. The study is based on the data on temporal dependences of pressure in the infrasonic wave collected by the I53US, I30JP, I59US, I46RU, I57US, and MAAG2 infrasonic stations included in the International Monitoring System (IMS) set up by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). The measurement data initially recorded on a relative scale were converted into absolute values. The temporal dependences of the infrasonic wave pressure were then filtered in the 1–40-s period range and were subsequently subjected to system spectral analysis that included the mutually complementary short-time Fourier transform, adaptive Fourier transform, and the wavelet transform with the Morlet wavelet as the basis function. As a result, it was found that the infrasonic signal amplitude exhibits quite a rapid decrease with distance between an infrasonic station and the meteoroid’s explosion site. The time delay of the infrasonic signal shows an increase with distance between the celestial body explosion and the site of signal detection. The signal celerity exhibits a dependence on the distance and the path orientation; it is estimated to be in the range of 269–308 m/s. The infrasonic signal duration shows virtually no dependence on the distance from the detonation point to an infrasonic station. The infrasonic signal spectra have a wide bandwidth with periods from ∼5 to ∼40 s. At the same time, the greatest energy falls within the isolated periods of 12–15 s and 28–33 s. The scatter diagrams and regressions for the infrasound main parameters were plotted. The celestial body’s kinetic energy (179 kt TNT) and acoustic efficiency (∼4%) were estimated from the prevailing infrasonic period.

Seismoacoustic effects of the Hovsgol earthquake (Mw = 4.9) of December 5, 2014

The results of study of the Hovsgol earthquake with M w = 4.9, which occurred on December 5, 2014, in the northern part of Hovsgol Lake in Mongolia, are presented. An infrasonic signal of ~140 s long was recorded by the Tory infrasonic station for the first time for the Baikal Rift System. On the basis of the source parameters and focal mechanism of this earthquake determined, displacements in the epicentral zone of the Hovsgol earthquake are modeled. It is shown that they could not have produced an infrasonic sound. The use of acceptable values of group velocities of infrasonic waves (0.28–0.35 km/s) demonstrates that the signal source was located approximately midway between the Tory station and the epicenter of the Hovsgol earthquake, indicating it was a secondary source. Based on the data on the azimuth and arrival time of the acoustic wave at the Tory station, the location of this secondary source is determined to have been on the northern slopes of the Khamar Daban Range. The infrasonic signal formed most likely by interaction between seismic waves from the earthquake and the mountain relief.

System spectral analysis of infrasonic signal generated by Chelyabinsk meteoroid

There are represented the results of the system spectral analysis using a set of linear and non-linear integral transformations for the time registrations of the acoustic signal generated by the Chelyabinsk meteoroid and registered by the Antarctic infrasonic station. The detailed time-frequency signal structure is analyzed.

Seismic and Infrasonic Analysis of the Major Bolide Event of 15 February 2013

Online Material: Tables of moment tensor solutions, station M s estimates, infrasonic signal parameters; figures of velocity models, simulated vertical component displacement time histories and spectra, Green’s functions. A major bolide event causing damage and injuries in a region of the Russian Federation east of the Ural Mountains occurred at approximately 03:20 GMT on the morning of 15 February 2013. The meteoroid entered the Earth’s atmosphere traveling from east‐to‐ west before final disintegration near the city of Chelyabinsk. Widespread damage was reported across the region, affecting more than 7000 buildings in several cities and resulting in injuries to over 1500 persons. Many fragments of the meteorite several centimeters in diameter have been recovered from the region surrounding Chelyabinsk. The meteorite will probably be named the Chebarkul meteorite due to large fragments having been recovered from near Lake Chebarkul, west of Chelyabinsk and near the apparent termination point of the meteorite track (Tauzin et al. , 2013, and references therein). In this article, we will refer to the event as the Chebarkul bolide. During the period of atmospheric traverse the Chebarkul bolide was recorded on infrasonic stations located as far away as Antarctica (Le Pichon et al. , 2013), and the terminal air blast coupled with the solid Earth to generate seismic surface waves visible on broadband seismographs to distances of over 4000 km (Tauzin et al. , 2013). Very few such events are sufficiently energetic to produce well‐observed seismic signals beyond a few hundred kilometers from the source (Yamada and Mori, 2010). The first estimate of the equivalent yield of the air blast by P. Brown of the University of Western Ontario (http://www.jpl.nasa.gov/news/news.php?release=2013-061, last accessed 25 February 2013) was nearly 500 kilotons (kt) of trinitrotoluene (TNT). The event is believed to be the most energetic bolide to have occurred since the 1908 event …

The 2013 Russian fireball largest ever detected by CTBTO infrasound sensors

AbstractOn 15 February 2013, a large Earth‐impacting fireball disintegrated over the Ural Mountains. This extraordinary event is, together with the 1908 Tunguska fireball, among the most energetic events ever instrumentally recorded. It generated infrasound returns, after circling the globe, at distances up to ~85,000 km, and was detected at 20 infrasonic stations of the global International Monitoring System (IMS). For the first time since the establishment of the IMS infrasound network, multiple arrivals involving waves that traveled twice round the globe have been clearly identified. A preliminary estimate of the explosive energy using empirical period‐yield scaling relations gives a value of 460 kt of TNT equivalent. In the context of the future verification of the Comprehensive Nuclear‐Test‐Ban Treaty, this event provides a prominent milestone for studying in detail infrasound propagation around the globe for almost 3 days as well as for calibrating the performance of the IMS network.

The Košice meteorite fall: Atmospheric trajectory, fragmentation, and orbit

AbstractThe Košice meteorite fall occurred in eastern Slovakia on February 28, 2010, 22:25 UT. The very bright bolide was imaged by three security video cameras from Hungary. Detailed bolide light curves were obtained through clouds by radiometers on seven cameras of the European Fireball Network. Records of sonic waves were found on six seismic and four infrasonic stations. An atmospheric dust cloud was observed the next morning before sunrise. After careful calibration, the video records were used to compute the bolide trajectory and velocity. The meteoroid, of estimated mass of 3500 kg, entered the atmosphere with a velocity of 15 km s−1 on a trajectory with a slope of 60° to the horizontal. The largest fragment ceased to be visible at a height of 17 km, where it was decelerated to 4.5 km s−1. A maximum brightness of absolute stellar magnitude about −18 was reached at a height of 36 km. We developed a detailed model of meteoroid atmospheric fragmentation to fit the observed light curve and deceleration. We found that Košice was a weak meteoroid, which started to fragment under the dynamic pressure of only 0.1 MPa and fragmented heavily under 1 MPa. In total, 78 meteorites were recovered in the predicted fall area during official searches. Other meteorites were found by private collectors. Known meteorite masses ranged from 0.56 g to 2.37 kg. The meteorites were classified as ordinary chondrites of type H5 and shock stage S3. The heliocentric orbit had a relatively large semimajor axis of 2.7 AU and aphelion distance of 4.5 ± 0.5 AU. Backward numerical integration of the preimpact orbit indicates possible large variations of the orbital elements in the past due to resonances with Jupiter.

Influence of near-source volcano topography on the acoustic wavefield and implication for source modeling

In near-source conditions (<5km), the atmosphere is often assumed to be fully transparent to acoustic waves and to have a small effect on the acoustic wavefield. As a consequence, the propagation of the acoustic waves in the atmosphere near the source is often neglected and waveform is compensated only in amplitude by the inverse of the distance from the source. However, the amplitude distribution at five infrasonic stations deployed around the active craters of the Stromboli volcano, reveals anomalous decay up to −11dB larger than expected, which cannot be explained in terms of energy loss for geometrical spreading. The distribution of amplitude decay changes for different source positions, suggesting a strong relationship with the source-to-receiver path geometry. By using 2D-FDTD modeling, we show that the anomalous amplitude distribution of the acoustic waves at Stromboli is not necessarily due to the source radiation pattern but it is strongly influenced by the topography of the ground–atmosphere interface. Diffraction and reflection of topography contaminate the acoustic wavefield and have a strong effect in reducing the amplitude and altering the waveform. Our work demonstrates that line-of-sight conditions are quite difficult to be achieved in acoustic experiments and that a detailed knowledge of the topography along the crater–receiver path is necessary whenever infrasound waveforms are used to invert for the source process.

Anomalous Infrasonic Waves Before a Small Earthquake in Beijing

AbstractAnomalous infrasound waves were recorded at five infrasonic monitoring stations four days before a small earthquake which happened in Beijing on 12 October 2011. Waveforms of these five signals are consistent, which are N‐shaped impulse waves with same duration of about one hour. Using the Wigner‐Ville distribution method, time‐frequency analysis of the signals suggests that waves' energies concentrate mainly below the frequency of 0.025 Hz. Correlation coefficients between two signals are all up to about 0.8. The infrasonic source is imaged and located by the method of beamforming, and the results show that distance between the source and epicenter is about 5 km. This study proves that low‐frequency atmospheric infrasonic waves may appear before earthquakes, so valuable information could be provided by studying this kind of infrasonic waves.

Infrasonic detection of a near-Earth object impact over Indonesia on 8 October 2009

[1] We present analysis of infrasonic signals produced by a large Earth-impacting fireball, believed to be among the most energetic instrumentally recorded during the last century that occurred on 8 October, 2009 over Indonesia. This extraordinary event, detected by 17 infrasonic stations of the global International Monitoring Network, generated stratospherically ducted infrasound returns at distances up to 17 500 km, the greatest range at which infrasound from a fireball has been detected since the 1908 Tunguska explosion. From these infrasonic records, we find the total source energy for this bolide as 8–67 kilotons of TNT equivalent explosive yield, with the favored best estimate near ∼50 kt. Global impact events of such energy are expected only once per decade and study of their impact effects can provide insight into the impactor threshold levels for ground damage and climate perturbations.

Estimated Green’s function extracted from superconducting gravimeters and seismometers

Estimated Green’s function (EGF) between stations has been extracted from ambient seismic noise, direct surface wave and coda waves. It is also confirmed by laboratory experiments on ultrasonics and theoretical derivations assuming diffusive wave field, equi-partition of modes or random sources on an enclosed surface. This method provides a new approach to study the crust and mantle structure at regional scale, continental scale and global scale. Following the achievements with seismometer records, the records of infrasonic station, hydrophone and microphone were also used to obtain the EGFs of different wave fields. Since superconducting gravimeter is a better long period instrument than regular seismometer, EGF at longer period is expected to be obtained with the cross correlation of gravity data. In this paper, we will show the EGFs extracted by cross-correlations between the superconducting gravimeters and the seismometers. Both the travel times and dispersion curves obtained from different data types are consistent. The result shows that it is possible to retrieve the deep structure by the cross correlation of gravity data.

On simulation of the atmospheric acoustic channel for some nuclear tests in former soviet test site Semipalatinsk

This paper presents data on the recording of infrasound from distant nuclear explosions set off in former soviet test site Semipalatinsk and recorded by infrasonic station Irkutsk–Badary of the Institute of Solar–Terrestrial Physics SB RAS in the Tunkinsky region in the Buryat Republic. We assess the state of the atmospheric acoustic channel (AAC) along the propagation path. Results of the AAC modeling are compared with experimental data.

Infrasound Radiated During the Montana Earthquake of 1959 August 18

Seismic waves caused by earthquakes radiate infrasound into the atmosphere as they proceed over the Earth's surface. Several instances of such sound waves radiated locally by seismic waves passing through the Washington, D.C., area have been observed at the infrasonic station there. A notable instance was the great Montana earthquake of 1959 August 18. Measurements of the radiated infrasound gave data on the seismic waves, including their travel times, local speeds, directions of travel, amplitudes, and waveforms.

On the Measurement of Infrasound

Summary The physical properties and propagation characteristics of atmospheric infrasound determine the techniques and instrumentation used for its measurement. The physical properties which influence the design of the measurement system for infrasound are summarized, and the techniques and instrumentation used for measurement are described. Propagation over long distances is influenced by temperature gradients and winds. Therefore a network of infrasonic stations has been established on a world-wide basis to carry on propagation researches. Investigators at the observatories have identified various geoacoustical sources of infrasound. This paper provides a description of the basic measurement system used at all of the stations in the network. We are concerned with the measurement of infrasound in the atmosphere, i.e. sound waves whose frequencies of oscillation are less than the lowest audible frequency (about 15 Hz). Of particular interest are those waves whose oscillation periods lie in the range of 1 *O-lOOO s, because such waves propagate for distances of thousands of kilometres without substantial loss of energy. Sounds at these frequencies are almost always present at measurable intensities. Those of natural origin have many causes, including volcanic explosions, earthquakes, waves on the seas, and large meteorites. Severe storms and the aurora in the northern hemisphere are often accompanied by infrasound. Man-made sources include powerful explosions and the shock waves from vehicles moving through the atmosphere at supersonic speeds, at altitudes below about 125 km. Brief preliminary descriptions of the basis for an infrasonic measurement system and for its design have already been published (Cook & Young 1962; Cook 1969). Here we review the earlier brief descriptions and provide a fuller definition of the techniques and basic instrumentation for measurement of infrasound. The passage of an infrasonic wave causes pressure oscillations as it traverses the atmosphere. For infrasound of natural origin, the amplitude p of the sound pressure is often in the range of 0.1-100dyncm-2, and infrasonic microphones are usually designed to respond to such pressures (the atmospheric pressure Po x lo6 dyn crn-'). Experience has shown that infrasonic waves observed at a station are approximately plane, propagating in a direction which is usually almost parallel to the Earth's surface. The several microphones at a station are all on the Earth's surface, and the speed of a line of constant phase for a sound wave travelling over the Earth's surface can be determined from the output of the several microphones. This speed c,, is usually