David N. Green

Ground Truth Events: Assessing the Capability of Infrasound Networks Using High Resolution Data Analyses

The purpose of building and maintaining an infrasound network is to be able to detect, identify, and locate low-frequency atmospheric pressure disturbances. In order to assess the capability of such a network, and to recognise potential weaknesses, the system must be tested using signals from well understood sources. Events which generate such signals are referred to as ground truth and are defined as being events for which the source location, origin time and acoustic generation mechanism are known through independent means. In ideal circumstances, a measure of the source magnitude should also be ascertained, and parameters influencing the acoustic radiation pattern such as local terrain and ground cover should be identified. Similar to seismic ground truth parameters (e.g., Bondar et al. 2004a), the infrasound ground truth parameters are associated with only the source. Meteorological parameters which influence the propagation of the acoustic waves (e.g., temperature and wind) are not considered ground truth, and it is often the accuracy of these atmospheric parameters that we wish to test using signals from ground truth events.

Local, regional, and remote seismo-acoustic observations of the April 2015 VEI 4 eruption of Calbuco volcano, Chile

The two major explosive phases of the 22–23 April 2015 eruption of Calbuco volcano, Chile produced powerful seismicity and infrasound. The eruption was recorded on seismo-acoustic stations out to 1,540 km and on 5 stations (IS02, IS08, IS09, IS27, and IS49) of the International Monitoring System (IMS) infrasound network at distances from 1,525 to 5,122 km. The remote IMS infrasound stations provide an accurate explosion chronology consistent with the regional and local seismo-acoustic data, and with previous studies of lightning and plume observations. We use the IMS network to detect and locate the eruption signals using a brute-force, grid-search, cross-bearings approach. After incorporating azimuth deviation corrections from stratospheric cross-winds using 3D ray-tracing, the estimated source location is 172 km from true. This case study highlights the significant capability of the IMS infrasound network to provide automated detection, characterization, and timing estimates of global explosive volcanic activity. Augmenting the IMS with regional seismo-acoustic networks will dramatically enhance volcanic signal detection, reduce latency, and improve discrimination capability.

Volcano Infrasound and the International Monitoring System

Volcanoes generate a wide variety of low-frequency (~0.01–20 Hz) acoustic signals, and infrasound technology is part of an expanding suite of geophysical tools available to characterize, understand, and monitor volcanic processes. We review recent advances in the field of volcano acoustics with an emphasis on scientific and potential civil application gains from the International Monitoring System (IMS) infrasound network. Energetic infrasound from explosive volcanism can propagate hundreds to thousands of kilometers in atmospheric waveguides and large explosive eruptions (which represent significant societal and economic hazards) are routinely recorded by the IMS infrasound network. Significant progress in understanding volcano infrasound has been made through dedicated local deployments (within <15 km of the source) in tandem with other observation systems. This research has identified diverse source mechanisms of volcanically generated infrasound, and elucidated the influence of near-source topography and local atmospheric conditions on acoustic propagation and recordings. Similarly, advances are being achieved in inferring volcanic source processes from signals recorded at the longer ranges typically associated with IMS detections. However, practical challenges remain in the optimization of remote volcano infrasound signal detection, discrimination, association, and location. Many of these challenges are the result of strong signal variability associated with long-range acoustic propagation through the temporally and spatially varying atmosphere. We review the state of knowledge on infrasound generation by explosive volcanism, and assess progress toward the development of infrasonic eruption early warning and notification systems at regional and global scales.

Automated detection and cataloging of global explosive volcanism using the International Monitoring System infrasound network

Explosive volcanic eruptions are among the most powerful sources of infrasound observed on earth, with recordings routinely made at ranges of hundreds to thousands of kilometers. These eruptions can also inject large volumes of ash into heavily traveled aviation corridors, thus posing a significant societal and economic hazard. Detecting and counting the global occurrence of explosive volcanism helps with progress toward several goals in earth sciences and has direct applications in volcanic hazard mitigation. This project aims to build a quantitative catalog of global explosive volcanic activity using the International Monitoring System (IMS) infrasound network. We are developing methodologies to search systematically through IMS infrasound array detection bulletins to identify signals of volcanic origin. We combine infrasound signal association and source location using a brute-force, grid-search, cross-bearings approach. The algorithm corrects for a background prior rate of coherent infrasound signals ...

The influence of shallow atmospheric structure on tropospheric ducted infrasound from the Buncefield oil depot explosion

The vapour cloud explosion which destroyed the Buncefield oil depot, UK, on 11th December 2005, has proven to be a benchmark ground truth event for infrasonic studies. The regional infrasonic returns, those that propagated in the stratosphere and thermosphere, have been analysed in detail elsewhere. Here, we present the results of a study into infrasound ducted in the troposphere, recorded within 250 km of the source as air‐to‐ground coupled waves by a dense seismometer network. These tropospheric arrivals exhibit large waveform differences across the UK, both in amplitude and waveform shape. We numerically model these infrasound arrivals using a wave number integration method, incorporating a velocity profile derived from the UK Met Office numerical weather prediction model. Although some of the waveform variability is due to ground conditions at the recording site, we show that consistent changes in waveform shape across a 200 km swath of stations are correlated with a change in the wind vector in the l...