Infrasound Propagation

Whitaker, Rodney W.; Norris, David E.

doi:10.1007/978-0-387-30441-0_82

Cited by 13 publications

(9 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the true outdoor case, reflection from ground with finite‐impedance or with near‐surface air turbulence excited by solar heating can produce additional frequency‐dependent phase shifts (Bies et al, ; Pierce, ) that may further obscure the phase coupling. The effects of impedance on low‐frequency sound waves are small (Embleton et al, ; Piercy et al, ) and thus typically neglected in infrasound research (e.g., Bass, ; Sutherland & Bass, ; Whitaker & Norris, ). Rigid lower boundary conditions have been previously used to achieve strong agreement between observed and synthetic waveforms (e.g., Fee et al, ; Kim & Lees, ; Kim et al, ; Lacanna & Ripepe, ), suggesting that the effects of finite impedance are negligible.…”

Section: Discussionmentioning

confidence: 99%

Investigating Spectral Distortion of Local Volcano Infrasound by Nonlinear Propagation at Sakurajima Volcano, Japan

et al. 2020

View full text Add to dashboard Cite

Sound waves generated by erupting volcanoes can be used to infer important source dynamics, yet acoustic source‐time functions may be distorted during propagation, even at local recording distances ( <15 km). The resulting uncertainty in source estimates can be reduced by improving constraints on propagation effects. We aim to quantify potential distortions caused by wave steepening during nonlinear propagation, with the aim of improving the accuracy of volcano‐acoustic source predictions. We hypothesize that wave steepening causes spectral energy transfer away from the dominant source frequency. To test this, we apply a previously developed single‐point, frequency domain, quadspectral density‐based nonlinearity indicator to 30 acoustic signals from Vulcanian explosion events at Sakurajima Volcano, Japan, in an 8‐day data set collected by five infrasound stations in 2013 with 2.3‐ to 6.2‐km range. We model these results with a 2‐D axisymmetric finite‐difference method that includes rigid topography, wind, and nonlinear propagation. Simulation results with flat ground indicate that wave steepening causes up to ∼2 dB (1% of source level) of cumulative upward spectral energy transfer for Sakurajima amplitudes. Correction for nonlinear propagation may therefore provide a valuable second‐order improvement in accuracy for source parameter estimates. However, simulations with wind and topography introduce variations in the indicator spectra on order of a few decibels. Nonrandom phase relationships generated during propagation or at the source may be misinterpreted as nonlinear spectral energy transfer. The nonlinearity indicator is therefore best suited to small source‐receiver distances (e.g., <2 km) and volcanoes with simple sources (e.g., gas‐rich strombolian explosions) and topography.

show abstract

Section: Discussionmentioning

confidence: 99%

Investigating Spectral Distortion of Local Volcano Infrasound by Nonlinear Propagation at Sakurajima Volcano, Japan

et al. 2020

View full text Add to dashboard Cite

show abstract

“…In contrast, here we model the radiation from a flat surface over the earthquake epicentre, showing that the measured signals are consistent with ground motion coupling directly above the hypocentre. Far‐field acoustic pressures are subsequently obtained using a time domain Parabolic Equation (TDPE) technique (Whitaker & Norris 2008). The far‐field acoustic pressures predicted at each array can then be compared with the pressure waveforms observed at the six arrays in this example.…”

Section: Introductionmentioning

confidence: 99%

“…After scaling the synthetic near‐source acoustic pressure by 0.005 to account for these radiation effects, we propagate this source term through the G2S model to each array using a TDPE technique (Whitaker & Norris 2008). The TDPE technique uses Fourier synthesis to derive the received waveform by combining simulations from a continuous wave PE in multiple frequency bins.…”

Section: Introductionmentioning

confidence: 99%

A seismoacoustic study of the 2011 January 3 Circleville earthquake

Arrowsmith

Burlacu

Pankow

et al. 2012

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YWe report on a unique set of infrasound observations from a single earthquake, the 2011 January 3 Circleville earthquake (M w 4.7, depth of 8 km), which was recorded by nine infrasound arrays in Utah. Based on an analysis of the signal arrival times and backazimuths at each array, we find that the infrasound arrivals at six arrays can be associated to the same source and that the source location is consistent with the earthquake epicentre. Results of propagation modelling indicate that the lack of associated arrivals at the remaining three arrays is due to path effects. Based on these findings we form the working hypothesis that the infrasound is generated by body waves causing the epicentral region to pump the atmosphere, akin to a baffled piston. To test this hypothesis, we have developed a numerical seismoacoustic model to simulate the generation of epicentral infrasound from earthquakes. We model the generation of seismic waves using a 3-D finite difference algorithm that accounts for the earthquake moment tensor, source time function, depth and local geology. The resultant acceleration-time histories on a 2-D grid at the surface then provide the initial conditions for modelling the near-field infrasonic pressure wave using the Rayleigh integral. Finally, we propagate the near-field source pressure through the Ground-to-Space atmospheric model using a time-domain Parabolic Equation technique. By comparing the resultant predictions with the six epicentral infrasound observations from the 2011 January 3, Circleville earthquake, we show that the observations agree well with our predictions. The predicted and observed amplitudes are within a factor of 2 (on average, the synthetic amplitudes are a factor of 1.6 larger than the observed amplitudes). In addition, arrivals are predicted at all six arrays where signals are observed, and importantly not predicted at the remaining three arrays. Durations are typically predicted to within a factor of 2, and in some cases much better. These results suggest that measured infrasound from the Circleville earthquake is consistent with the generation of infrasound from body waves in the epicentral region.

show abstract

“…This model accounts for 3‐D refraction, attenuation, absorption, and horizontal translation of the raypath from wind. However, raypath modeling does not account for scattering and diffraction [ Whitaker and Norris , 2008] and thus can lead to unrealistic propagation estimates. Approximate travel times reported here incorporate InfraMAP's eigenray solutions that determine matching raypaths that propagate to the receiver within a given distance and height tolerance (2 km).…”

Section: Methodsmentioning

confidence: 99%

“…Diffraction is accounted for, which is important for shadow zones between predicted eigenrays, near the surface, and long wavelength (infrasonic) propagation. It is important to note that the PE has inherent phase errors above ∼35° elevation from the source, so acoustic transmission loss at high launch angles is not as well constrained [ Whitaker and Norris , 2008]. The combination of PE and ray theory used here provides estimates of travel times, propagation paths, and transmission loss for remote sources.…”

Section: Methodsmentioning

confidence: 99%

Characterization of the 2008 Kasatochi and Okmok eruptions using remote infrasound arrays

2010

View full text Add to dashboard Cite

[1] The 2008 Plinian eruptions of Kasatochi and Okmok volcanoes were recorded by six remote International Monitoring System infrasound arrays. High-amplitude infrasound at these stations, combined with remote sensing, permits insight into important volcanic source parameters, such as origin times, durations, and source characteristics. Infrasound from the 7-8 August Kasatochi eruption consists of three well-defined eruption pulses, with the first two steam-rich and the last ash-rich. Pulse 2 is the most energetic and impulsive. Okmok produced over 9 h of continuous infrasound on 12-13 July. Acoustic propagation modeling for the Okmok eruption and first Kasatochi pulse predict thermospheric ducting and origin times consistent with seismic and satellite observations. However, theoretical acoustic origin times of pulses 2-3 are predicted to occur ∼15 min earlier than the seismic. Stratospheric ducting for these later pulses provides more consistent origin times. Although both volcanoes ejected ash into the stratosphere (>15 km), Kasatochi produced higher amplitude infrasound than Okmok. Previous studies have shown sustained infrasound with frequencies <0.5 Hz is indicative of high-altitude ash emissions. Kasatochi and Okmok recordings are consistent with this, as stratospheric emissions evident in satellite imagery are correlated with sustained 0.01-0.5 Hz infrasound. Further, the acoustic spectrum shape resembles the spectrum from man-made jets, suggesting a self-similar noise generation mechanism proposed in earlier work. Although uncertainties exist, observations and propagation modeling from Kasatochi suggest self-similarity is apparent at long distances (>2000 km) and does not seem to be appreciably affected by changes in ash content between the eruption pulses.

show abstract

Infrasound Propagation

Cited by 13 publications

References 27 publications

Investigating Spectral Distortion of Local Volcano Infrasound by Nonlinear Propagation at Sakurajima Volcano, Japan

Investigating Spectral Distortion of Local Volcano Infrasound by Nonlinear Propagation at Sakurajima Volcano, Japan

A seismoacoustic study of the 2011 January 3 Circleville earthquake

Characterization of the 2008 Kasatochi and Okmok eruptions using remote infrasound arrays

Contact Info

Product

Resources

About