Infrasound Monitoring Research Articles

Infrasound sensing: toward new measurement methods and controlled sources

The infrasound waves have already demonstrated their potential to characterize natural and man-made sources and to image the structure of atmosphere. These scientific acheivements have been driven mainly infrasound sensing by pressure sensor arrays deployed on the ground, with a strong contribution by permanent arrays developed in the framework of CTBT. However new infrasound sensing methods have been developed during the past two decades with very different concepts that allow to sense these waves at different altitudes in the atmosphere. We will recall a few key results associated with these new sensing methods on satellite and balloon platforms, as well as the ones using ionospheric perturbations. Concerning the infrasound sensing at ground level, we will explain how the infrasound waves can be monitored through ground movements and illustrate this method by the detection of infrasonic waves on Mars by SEIS seismometer of InSight NASA mission. Advantages and drawbacks of infrasound monitoring through ground movements will be presented, in particular the sensitivity to wind. Preliminary results comparing different infrasound sensing methods on the Earth will be presented. Eventually, we will also discuss shortly controlled infrasound sources and illustrate this discussion with recent experiments using burners as an infrasound source.

Studying infrasound propagation in the middle atmosphere with ICON and UA-ICON: comparison with the IFS and ground-based remote sensing

Infrasound signals are used to monitor various anthropogenic and natural sources. In particular, infrasound is one of the four verification technologies used by the International Monitoring System (IMS) of the Comprehensive Test-Ban Treaty organisation (CTBTO). To determine accurate source locations and energies, an accurate model of wind and temperature up to the lower thermosphere is necessary, hence operational NWP products are of great importance for routine infrasound monitoring activities. However, many of these models focus on tropospheric conditions, and the middle atmosphere (MA) is not well represented. UA-ICON is an upper atmosphere version of the ICON model that provides modelled atmospheric parameters up to 150 km. First, to assess ICON and IFS operational analysis products, comparisons to lidar observations are made. The main differences between both products were analysed with respect to winds and temperatures in the MA. Second, UA-ICON simulations outputs were compared to ICON and IFS fields to demonstrate the increased wave activity above ~30 km with UA-ICON. The added value of UA-ICON with respect to ICON and IFS for infrasound propagation simulations is discussed. The comparisons between the instrumental observations and the models will be presented, as well as comparisons between modelled and measured infrasound propagation.

Dynamics of rain-triggered lahars and destructive power inferred from seismo-acoustic arrays and time-lapse camera correlation at Volcán de Fuego, Guatemala

AbstractLahars, or volcanic mudflows, are one of the most devastating natural, volcanic hazards. Deadly lahars, such as the one that occurred after the Nevado del Ruiz, Columbia eruption in 1985, in which at least 23,000 people tragically lost their lives, threaten the safety and well-being of humans, the economy, and the infrastructure of many of the communities living in the vicinity of volcanoes. Due to their complex flow behaviors, lahars remain a major challenge to those studying them. We present an analysis of several rain-triggered lahar events at Volcán Fuego in Guatemala using both seismic and infrasound monitoring to quantify both ground vibrations and low-frequency atmospheric sound waves associated with these mudflows. Geophysical data collected over this field campaign quantifies flow parameters such as velocities, stage and the frequency of these rain-triggered lahars. Time-lapse imagery of lahar flows is compared with filtered seismo-acoustic signal characteristics to ascertain stage predictions and relationship to stage fluxes. Using random forest regression models, we establish moderate correlations (correlation coefficient modes 0.48–0.53) with statistical significance (p value = 0.01–0.02) between signal energetics and respective stage. Compiling a catalog of rain-triggered lahar events in Volcán de Fuego’s drainages over a season permits a dataset amenable to statistical analysis. Our goal is the development of new-generation geophysical monitoring tools that will be capable of remote and real-time estimation of flow parameters.

The use of a low-cost, small-aperture array as an auxiliary tool to improve infrasound monitoring in the Azores region

AbstractThe 2022’s seismo-volcanic crisis on São Jorge Island of the Azores archipelago has provided an opportunity to deploy a portable infrasound array as a collaborative work between the Research Institute for Volcanology and Risk Assessment (IVAR) of the University of the Azores (UAc) and the University of Florence (UniFI). The four-element array, SJ1, became operational on 2 April 2022. Despite being deployed in a first stage to monitor the activities related to the volcanic unrest on São Jorge Island, SJ1 worked as a supporting tool to the existing IMS infrasound station IS42, located on Graciosa Island at ~ 40 km distance, leading to an enhancement of the infrasonic monitoring network in the region. This work emphasises the importance of low-cost portable infrasound arrays to improve the coverage of infrasound observations for local and regional monitoring purposes in the Azores region. Two events recorded by both arrays are briefly exemplified: a low-magnitude earthquake on São Jorge Island and a fireball which crossed the North Atlantic Ocean. Infrasound data from both arrays are combined to obtain a fast but still accurate source localization of the analysed events.

Estimating infrasonic noise levels using a high resolution weather model

The presence of turbulence and other wind-induced pressure fluctuations are considered a nuisance in infrasound monitoring. For this reason, wind noise filters are typically in place for suppression. In this study, we establish a relation between microbarometer observations and in situ turbulence measurements at the Cabauw Atmospheric Research Site in The Netherlands. Using this relation, we forecast turbulent pressure levels using forecasted levels of turbulence kinetic energy (TKE) that are computed as part of the high-resolution (2.5 × 2.5 km grid scale) HARMONIE weather model. The estimates are compared with pressure noise levels as a function of frequency. This approach has two foreseen applications: (1) the forecasted turbulence fields could possibly help in site selection for infrasound arrays and (2) microbarometer observations could possibly be of use in the further refining of sub-grid scale turbulence schemes in weather models.

On the Use of a Complex Indicator of the Stability of Permutation Entropy of Time Series Fragments When Analyzing Infrasound Monitoring Signals of the Altai Republic

This paper discusses one of the approaches that allows us to assess the degree of complexity or randomness of fragments of a time series in order to detect infrasound or geomagnetic signals in the results of observations of the dynamics of the natural or man-made processes under study. In our case, we are talking about monitoring the infrasound background on the territory of the Altai Republic. To solve the problem of estimating the required characteristics of a time series with minimal computational costs and in real time, a complex indicator of the stability of permutation entropy is introduced, since estimating the value of classical permutation entropy for n = 3 (the most commonly used version of permutation entropy) does not allow solving the problem with sufficient accuracy.

Exploring Background Noise With a Large‐N Infrasound Array: Waterfalls, Thunderstorms, and Earthquakes

AbstractAmbient infrasound noise contains an abundance of information that is typically overlooked due to limitations of typical infrasound arrays. To evaluate the ability of large‐N infrasound arrays to identify weak signals hidden in background noise, we examine data from a 22‐element array in central Idaho, USA, spanning 58 days using a standard beamforming method. Our results include nearly continuous detections of diverse weak signals from infrasonic radiators, sometimes at surprising distances. We observe infrasound from both local (8 km) and distant (195 km) waterfalls. Thunderstorms and earthquakes are also notable sources, with distant thunderstorm infrasound observed from ∼800 to 900 km away. Our findings show that large‐N infrasound arrays can detect very weak signals below instrument and environmental noise floors, including from multiple simultaneous sources, enabling new infrasound monitoring applications and helping map the composition of background noise wavefields.

Evolving infrasound measurement and growing infrasound monitoring network

Infrasound carries information useful for detecting a strong natural phenomenon such as volcanic eruption and tsunami, which may cause catastrophic disaster. Therefore, infrasound measurement is gathering attention for potential applications in disaster prevention and life protection. However, the methodology of its measurement has not been well established except a few specific applications such as Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Some sensor devices employ Micro Electro Mechanical Systems (MEMS) sensors, which are, in general, small and available at a low price. This advantage enables us to increase the number of locations where infrasound can be monitored at multiple observation points. Another attempt is to assemble multiple sensors of different characters for widening dynamic range and frequency coverage of the sensor. These progress in infrasound measurement would make it possible to utilize infrasound in various purposes. In this respect, infrasound measurement needs to be standardized because one may want to analyze infrasound data together with those acquired using different devices by other organizations. At the same time, a platform for sharing infrasound data is becoming important to accelerate such usage. This paper overviews recent development of sensor devices for infrasound measurement and sensor deployment on going in Japan.

Local Infrasound Monitoring of Lava Eruptions at Nyiragongo Volcano (D.R. Congo) Using Urban and Near‐Source Stations

AbstractDuring eruptions, volcanoes produce air‐pressure waves inaudible for the human ear called infrasound, which are very helpful for detecting early signs of magma at the surface. Compared to violent ash‐rich explosions, recording more discrete atmospheric disturbances from effusive eruptions remains a practical challenge depending on the distance to the source. At Nyiragongo volcano (D.R. Congo), towering above a 1‐million urban area, we analyzed local infrasonic records between January 2018 and April 2022. An acoustic signature from this open‐vent volcano is detected up to the volcano observatory facilities in Goma city center about 17 km from its crater. We compared infrasound signals with space‐based observations of the intra‐crater activity (SO2 emissions, thermal anomalies, crater depth/radius). We thus obtain a comprehensive picture of Nyiragongo's eruptive activity during this period, encompassing the drainage of its lava lake during its third known flank eruption on 22 May 2021.

Causes and prevention and control measures for geological disasters: case studies from landslides and debris flows

Geological disasters are highly hazardous, and the corresponding means of measures should be selected for different monitoring and prevention, depending on the diversity of the size, type and level of the geological hazard. This paper focuses on two geological disasters, landslides and debris flows, which are different in nature but related to geological and other conditions highly prevalent in China's mountainous areas. The main causal mechanisms of landslide hazards include geological, climatic, and triggering conditions. Monitoring methods are mainly through instrumentation, which allows for more accurate monitoring of deformation and changes in water volume. The main mechanisms for debris flow hazards include geological, material, and water conditions. Monitoring debris flows includes mud level monitoring, rainfall monitoring and other monitoring such as infrasound monitoring. In disaster management, consideration should be given to the prevention and control of the natural environment as well as to the regulation and restriction of human production and living activities, with particular attention to the early prevention and control of special disaster-prone areas.

Detections of Infrasound Waves From Water Discharges at a Hydroelectric Dam: Implementation of Timely Warnings for Unexpected Discharge Events

AbstractWater discharges at hydroelectric dams on the Imjin River, which flows through North and South Korea, generate abrupt water level increases downstream. We assessed infrasound signals from water discharges using an infrasound array located ∼32 km from the source and applied infrasound detection in a flash flood alert system. Using infrasound signals, there was a 79% detection rate for 48 water level increase events occurring in the river downstream during a 14‐year period (2008–2021). The detected signals had a low amplitude, long duration, and broad frequency range (0.5–15 Hz). The energy curves of the detected infrasound signals for selected events showed good correlations with the onset times and water level variations in water level records. These results demonstrate that infrasound monitoring can serve as a practical early warning system for impending flash floods resulting from unnoticed water discharges or sudden debris flows in mountainous regions.

Infrasound detection of approaching lahars

Infrasound may be used to detect the approach of hazardous volcanic mudflows, known as lahars, tens of minutes before their flow fronts arrive. We have analyzed signals from more than 20 secondary lahars caused by precipitation events at Fuego Volcano during Guatemala’s rainy season in May through October of 2022. We are able to quantify the capabilities of infrasound monitoring through comparison with seismic data, time lapse camera imagery, and high-resolution video of a well-recorded event on August 17. We determine that infrasound sensors, deployed adjacent to the lahar path and in small-aperture (10 s of meters) arrays, are particularly sensitive to remote detection of lahars, including small-sized events, at distances of at least 5 km. At Fuego Volcano these detections could be used to provide timely alerts of up to 30 min before lahars arrive at a downstream monitoring site, such as in the frequently impacted Ceniza drainage. We propose that continuous infrasound monitoring, from locations adjacent to a drainage, may complement seismic monitoring and serve as a valuable tool to help identify approaching hazards. On the other hand, infrasound arrays located a kilometer or more from the lahar path can be effectively used to track a lahar’s progression.

Contribution to Uncertainty Propagation Associated with On-Site Calibration of Infrasound Monitoring Systems

To improve the confidence and quality of measurements produced by regional and international infrasound monitoring networks, this work investigates a methodology for propagating uncertainty associated with on-site measurement systems. We focus on the propagation of sensor calibration uncertainties. The proposed approach is applied to synthetic infrasound signals with known back azimuth and trace velocity, recorded at the array elements. Relevant input uncertainties are investigated for propagation targeting the incoming signals (noise), instrumentation (microbarometers, calibration system, wind noise reduction system), and the time-delay-of-arrival (TDOA) model (frequency band). Uncertainty propagation is performed using the Monte Carlo method to obtain the corresponding uncertainties of the relevant output quantities of interest, namely back azimuth and trace velocity. The results indicate that, at high frequencies, large sensor uncertainties are acceptable. However, at low frequencies (<0.1 Hz), even a 2∘ sensor phase uncertainty can lead to errors in the back azimuth of up to 5∘ and errors in the trace velocity of 20 m/s.

Seismoacoustic Coupled Signals from the 11 July 2020 Ms 5.1 Tangshan, China, Earthquake

ABSTRACT The Ms 5.1 Tangshan earthquake that occurred on 11 July 2020 was recorded by the infrasound array DQS at a source-to-receiver distance of 196 km and an azimuth of 278°. Relatively high-apparent velocity, celerity of epicenter infrasound, and propagation modeling indicate a stratospheric arrival. The backprojection of the epicentral infrasound detection delineates a northeast direction-extended infrasound radiation region with a long axis of about 57 km and a short axis of about 28 km, which is in good agreement with the fault rupture direction. The robustness of the infrasound radiation source location is also tested. The consistency between the spatial distribution of the radiation source and the epicenter confirms that the extended radiating zone around the epicenter excited infrasound signals lasting 2.5 min at a distance of 196 km. A comparison between the backprojected sound pressure level and peak surface pressure derived from measured seismic ground motions shows some disagreement, which may involve propagation path and/or topography around the epicenter. Therefore, these factors should be taken into account when locating the sources of infrasound and estimating the distribution of ground motion. This study shows the ability of infrasound arrays to detect, locate, and research moderate earthquakes and help reconstruct the seismoacoustic coupling in the source region and fault rupture. Moreover, the complexity of the infrasound radiation source and seismoacoustic coupling mechanism is recognized. It is expected that infrasonic observations of moderate earthquakes will increase with the number of infrasound arrays deployed worldwide. Our study is also helpful to the scientific design and optimal layout of infrasound monitoring systems, which will allow for the detection of earthquakes in addition to explosive sources.

Monitoring of Indonesian volcanoes with the IS06 infrasound array

Detecting and notifying ongoing volcanic explosive eruptions is crucial in supporting the Volcanic Ash Advisory Centre (VAAC). However, local monitoring systems are missing at many active volcanoes, but long range infrasound monitoring might provide useful information if able to detect and notify volcanic explosive events. Indeed, many studies have already highlighted the utility and the potential of long-range infrasound monitoring for this aim, but still open questions remain concerning its actual efficiency and reliability. In this study we investigate the potential of the IS06 array (Cocos Island, Australia) of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to remotely detect volcanic explosive eruptions in the Indonesian Arc between 2012 and 2019, when 11 volcanoes, positioned at a distance between 1000 and 2000 km from the array, erupted with an energy spanning from mild explosions to VEI (Volcanic Explosivity Index) 4 eruptions. For each volcano, using infrasonic data recorded at a single array and accounting for realistic infrasound propagation conditions, we calculate a range corrected Infrasound Parameter (IP) and propose two additional empirical thresholds on signal strength and persistency. The IP is used eventually to define an alert whenever an established threshold is exceeded and the corresponding reliability estimated. Results show that the range corrected IP is highly reliable for events VEI = 3 or greater under favorable propagation conditions, but smaller scale short-lasting explosive eruptions still remain usually undetected. Unresolved ambiguity remains due to short spacing among volcanoes with respect to the array. For regional scale monitoring purposes, this can be solved only considering volcanic sectors rather than single volcanic edifices that, despite preventing unambiguous notification of a given volcano, might allow to increase the attention of the VAAC over a specific area.

Long range infrasound monitoring of Yasur volcano

The atmospheric injection of gas and material produced by an explosive volcanic eruption determines a rapid compression of the atmosphere, which subsequently propagates as longitudinal elastic waves (sound). The size of the source, generally greater than tens of meters, and its duration, longer than a few seconds, result into an emitted signal that is particularly rich in low frequencies (f < 20 Hz), thus determining an efficient infrasound radiation. Thanks to the low spectral content and the reduced attenuation in the atmosphere, infrasound is capable of propagating for very large distances.In this study we show how the infrasonic monitoring at regional distances (> 100 km) is efficient in recording and characterizing volcanic events. For the purpose of our study, infrasound signal radiated from Yasur volcano (Tanna Island, Vanuatu) was studied for a period of twelve years (January 2008 – December 2019). Signals from Yasur were registered at a source-to-receiver distance of 400 km by the IS22 infrasound array, located in New Caledonia, part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS). The predominantly explosive Strombolian activity of this volcano makes it a perfect subject to be studied by infrasound technology. Detections of volcanic infrasound are modulated according to the seasonal variation of stratospheric winds and corrected for attenuation accounting for real atmospheric specification between the source and the receiver to retrieve the pressure at the source. Next, they are used to evaluate long-term (yearly) and short term (hourly) variations of activity over the period of analysis. Results are compared with thermal anomalies recorded by the MODerate resolution Imaging Spectroradiometer (MODIS) installed on NASA's Terra and Aqua satellites.We show that even at regional distances (400 km) it is possible to follow the long term (yearly) fluctuations of ordinary explosive activity during periods of optimal propagation of infrasonic waves in the atmosphere. In addition, we show that the time resolution retrieved from the signal analysis allows to follow variations of volcanic activity at hourly time scale, thus representing a valuable source of information, in particular in areas where local geophysical observations are missing.

Infrasound- implications for human medicine

Infrasound describes ubiquitous, low-frequency sound (< 20 Hz) in the environment with along wavelength below the median hearing threshold, which can nevertheless be heard and tactilely perceived, depending on the sound pressure level and frequency spectrum. In nature, infrasound emissions usually occur only in the low-threshold range. Nevertheless, after strong and chronic exposure to usually artificially generated infrasound emissions, various effects on the ear and the body, sometimes questionably critical to health, can be observed. Correct measurement and assessment of infrasound sources is complex and controversial. Established guidelines are scarce. Innovative research areas include infrasound monitoring for evaluation of natural events and infrasound applications in medicine. In the future, it is hoped that new insights will be gained from infrasound research and that amore extensive classification in occupational medicine will be possible.

Global shockwaves of the Hunga Tonga-Hunga Ha’apai volcano eruption measured at ground stations

The eruption of the Tonga volcano created globally propagating spherical shockwaves in the atmosphere. Analyses are done to data from two southern U.S. stations of the author sampling at 3-21s intervals and 189 weather stations at 1-5min intervals. The shockwaves arrived from two routes in the atmosphere: the shortest spherical arc and the longer spherical arc through the antipole. In most stations, signals up to the 6th path of shockwaves were recorded as the waves traveled around the globe multiple times. The speed of shockwaves is estimated to be 309.5± 2.9m/s, consistent with the speed of sound at the top of the troposphere where a waveguide exists. Discussion is made on the post-shockwave ringing of 4-8min as higher amplitude oscillations above the level of pre-shockwaves background noise. A theoretical wave dispersion is derived which verifies that the spherical shockwave's phase speed is the same as the speed of sound.

Infrasound generated by meteorological fronts as a background for infrasound monitoring of explosions

The results of study of temporal variations of the characteristics of infrasound (amplitudes, coherences, grazing angles, azimuths and horizontal phase speeds) detected during a passage of warm and cold fronts through the networks of microbarometers in the Moscow region are presented. .Infrasound radiated during periods of weather changes is an almost continuous background against which infrasound monitoring of explosions in the atmosphere is carried out. The significant differences observed in the characteristics of infrasound from warm and cold fronts are found. Such differences must be taken into account when detecting infrasound precursors of atmospheric storms. A possible aerodynamic mechanism for the generation of infrasound caused by the turbulent air flow around the geometric irregularities of the surface of meteorological front is proposed. [Work supported by RSF Grant No. 21-17-00021.]

Multi-parametric Experiments on Infrasound Monitoring for Snow-Avalanche at Mt. Fuji

Multi-parametric Experiments on Infrasound Monitoring for Snow-Avalanche at Mt. Fuji