Infrasound generated by earthquakes and explosions is generally detected at receivers at epicentral distances of hundreds to thousands of kilometers. However, proximal (< 50 km) observations are especially important for low-magnitude earthquakes and low-yield explosions that may not generate signals capable of being detected at great ranges. Here, we present on the signals detected on an infrasound array 3 km away from two ML 2.9 earthquakes in the Permian Basin of west Texas. Local infrasound (LIS), generated at receivers during the passage of seismic waves, was detected following each earthquake. Epicentral infrasound (EIS), created at or near the epicenter and propagating away as a sound wave, was also detected. Array processing methods show that the EIS signals arrive from the same direction as the earthquake epicenters and at acoustic speeds. To our knowledge, these are the first observations of laterally propagating EIS at proximal ranges following an earthquake of any magnitude.
Avalanches are natural hazards that occur when an unstable mass of snow breaks away from a mountain slope. It is expected that climate change will lead to increased avalanche activity, which can cause interruptions to water and power infrastructure, transportation blockages, higher risk for loss of life, and changes to ecosystems. Avalanche forecasts are key to mitigating hazards, and observations of recent avalanches comprise one of the key observations for deciding danger level. It is well understood that infrasound can be used to detect and locate snow avalanches in transitional snowpacks, even during snowstorms, but similar studies are lacking for maritime snowpacks. Here we show results from an infrasound field experiment in Tutl’uh (Turnagain Arm), Alaska, USA between January 31 – April 30 field deployment campaign. We show that (1) methods developed for transitional snowpacks can be applied to maritime snowpacks in Alaska, (2) background noise may be higher in this region due to natural and anthropogenic influences, and (3) low-cost infrasound sensors can withstand the harsh Alaskan winter and successfully collect data. We also discuss the impact of this work and a path forward.
Accurately locating sources of seismic and infrasonic energy is integral to global monitoring of earthquakes and explosions. Infrasound arrivals times can be used to calculate the origins of events that generate acoustic energy. Picking times of emergent infrasound arrivals, however, can be difficult and prone to uncertainty. Reverse time migration (RTM) is a waveform based location method that does not rely on picked arrival times. Here we use RTM to locate a known chemical explosion that generated acoustic and acoustic-to-seismic signals on 26 and 108 receivers, respectively. All location predictions are less than 24 km from the known location with time errors of less than three minutes. We find strong overall agreement between our results and those of existing RTM and arrival time based methods. Our initial results suggest that RTM is a promising method of event location using acoustic arrivals recorded on both infrasound and seismic instrumentation.
Infrasound observations have grown increasingly important for the monitoring of earthquakes. While large earthquakes generate infrasound that can be detected thousands of kilometers away, there are few near-field observations of infrasound generated by low-magnitude events. We describe preliminary results of the West Texas Acoustic Experiment, during which infrasound sensors collected continuous data in the Permian Basin for a six-month period spanning January—June 2023. During this time, more than 1000 earthquakes with magnitudes between 1.2 and 4.2 occurred within 50 km of the network. We used spectral analysis, array processing, and manual inspection of waveforms to evaluate arrivals of infrasound signals following 84 events with magnitudes between 2.5 and 4.2. Here, we describe eight such events and the infrasound signals associated with each. We find detections of seismic-to-acoustic infrasound signals associated with seven events. We also find strong evidence of a laterally-propagating, purely acoustic wave generated by an M2.9 earthquake.
