Persistent, “Mysterious” Seismoacoustic Signals Reported in Oklahoma State during 2019

Abstract

We report on the source of seismoacoustic pulses that were observed across the state of Oklahoma (OK) during summer of 2019, and the subject of national media coverage and speculation. Seismic network data collected across four U.S. states and interviews with witnesses to the pulse’s effect on residential structures demonstrate that they were triggered by routine ammunition disposal operations conducted by McAlester Army Ammunition Plant (McAAP). During these operations, conventional explosives destroy obsolete munitions stored in pits through a controlled sequence of electronically timed shots that occur over tens of minutes. Despite noise-abatement efforts that reduce coupling of acoustic energy with air, some lower frequency, subaudible (infrasonic) sound radiates from these shots as discrete pulses. We use nine months of blast log documents, seismic network records, analyst picks, and physical modeling to demonstrate that seismic stations as far as 640 km from McAAP sample these pulses, which record seasonal patterns in stratospheric and tropospheric winds, as well as the dynamic formation of waveguides and shadow zones. Digital short-term average to long-term average detectors that we augment with dynamic thresholds and time-binning operations identify these pulses with a fair probability, when compared with visual observations. Our analyses thereby provide estimates of observation rates for both partial and full sequences of these pulses, as well as single shots. We suggest that disposal operations can exploit existing, composite seismic networks to predict where residents are likely to witness blasting. Crucially, our data also show that dense seismic networks can record multiscale atmospheric processes in the absence of infrasound arrays.

Evidence for Short Temporal Atmospheric Variations Observed by Infrasonic Signals: 1. The Troposphere

“…This study is based on a repetitive, active source located at the McAlester Army Ammunition Plant (McAAP), Oklahoma, USA. The data acquisition took place between January 13, 2021, and March 2, 2021, and the location is motivated by Carmichael et al (2021) who studied seismoacoustic signals originated from the same source. One of McAAP's missions is to destroy old ammunition by detonating it.…”

Identifying attacks in the Russia–Ukraine conflict using seismic array data

“…Acoustic and seismic ranging methods have been used from as early as the First World War for locating artillery positions and were fundamental to the development of modern-day seismic exploration methods 6 – 8 . Methods have since evolved to focus either on locating artillery positions and impact areas using acoustic sensors from experimental datasets 9 or to infer properties of individual large explosions 1 , 2 , 10 . However, the real-time analysis of seismic and acoustic signals from an active military conflict is, so far, absent in the literature, in part owing to a lack of suitable data.…”

“… Seismometers are generally used by the research community to study local or distant earthquakes, but seismograms also contain critical observations from regional 1 , 2 and global explosions 3 , which can be used to better understand conflicts and identify potential breaches of international law. Although seismic, infrasound and hydroacoustic technology is used by the International Monitoring System 4 to monitor nuclear explosions as part of the Comprehensive Nuclear-Test-Ban Treaty, the detection and location of lower-yield military attacks requires a network of sensors much closer to the source of the explosions.…”

Evidence for Short Temporal Atmospheric Variations Observed by Infrasonic Signals: 2. The Stratosphere

“…In Area 1, the pits are arranged in a circular shape; in Area 2, they are located along a straight line. Schematics of the areas' geometries can be found in Carmichael et al (2021) and Averbuch et al (2022). Almost every day, the pits are filled up with old ammunition and detonated in 20 s intervals.…”

“…Schematics of the areas' geometries can be found in Carmichael et al. (2021) and Averbuch et al. (2022).…”