Observation of Infrasonic/Acoustic/Seismic Waves Induced by Hypersonic Reentry of Hayabusa
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Reentry
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Over the last century, seismic instruments have recorded, with increasing frequency, the ground motion produced by meteorically generated shock waves striking the Earth's surface. In this review, the history of meteor‐related seismic signals is discussed, along with documented waveform characteristics, source mechanisms, air‐ground coupling phenomena, and kinematic methods of determining meteor trajectories and event locations. Uncertainties in the mechanics of air‐ground coupling, however, have left methods of measuring meteor source energy underdeveloped. To date, coupling of acoustic waves directly with the Earth's surface represents the bulk of the observed meteor‐related seismic signals, while precursory and impact‐related seismic waves remain an observational rarity. With proliferation of infrasound and seismic monitoring systems, new opportunities exist to explore the relationship between Earth's atmosphere and surface. Continued study of meteor seismology will lead to new methods to constrain energies, sizes, and fluxes for moderately (cm to m) sized meteoroids on Earth and potentially on Mars.
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Microphones and seismographs were co-located in arrays on Skidaway Island, Georgia, for the launchings of Apollo 13 and 14, 374 km to the south. Simultaneous acoustic and seismic waves were recorded for both events at times appropriate to the arrival of the acoustic waves from the source. Significant comparisons of the true signals are (1) the acoustic signal is relatively broadband compared to the nearly monochromatic seismic signal; (2) the seismic signal is much more continuous than the more pulse-like acoustic signal; (3) ground loading from the pressure variations of the acoustic waves is shown to be too small to account for the seismic waves; (4) the measured phase velocities of both acoustic and seismic waves across the local instrument arrays differ by less than 6 per cent and possibly 3 per cent if experimental error is included. It is concluded that the seismic waves are generated by resonant coupling to the acoustic waves along some 10 km of path on Skidaway Island. The thickness of unconsolidated sediment on the island is appropriate to a resonant ground wave frequency of 3.5 to 4 Hz, as observed. Under appropriate conditions, ground wave observations may prove more effective means of detecting certain aspects of acoustic signals in view of the filtering of wind noise and amplification through resonance.
Microseism
Seismometer
Dispersive body waves
Rayleigh Wave
Seismic Noise
SIGNAL (programming language)
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In this paper we consider the numerical solution to the problem of the infrasonic and seismic wave propagation for the spatial inhomogeneous model Atmosphere-Earth. The interface between the atmosphere and the elastic medium is assumed to be curvilinear. The efficient numerical algorithm for carrying out calculations on multi-processor computer systems is described. A specific feature of the algorithm proposed is a combination of integral transforms and the finite difference method. The propagation of infrasonic waves in the isothermal atmosphere is described by the linearized Navier-Stokes equations in the form of the hyperbolic first order system in the 3D Cartesian coordinate system. The propagation of seismic waves in the lithosphere is described by the hyperbolic first order system in terms of the displacement velocity vector and stress tensor according to elasticity theory. In this paper we present the results of numerical modeling of wave fields for the test models in the case when the interface between the atmosphere and elastic half-space is curvilinear.
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Abstract The mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere. We numerically simulate this coupled system for two application cases: active seismic experiments (ASEs) and passive seismic experiments. A recent ASE (Krishnamoorthy et al., 2018, https://doi.org/10.1002/2018GL077481 ) observed the infrasonic signals produced by a seismic hammer. To measure the sensitivity of observations to seismic parameters, we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock‐solid subsurface. At long range, we investigate the influence of the source by using two focal mechanisms. We found surface waves generate an infrasonic plane head wave in the ASE case of the rock‐solid material. For the passive seismic experiments, the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail. Despite some limitations, the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties.
Dispersive body waves
Microseism
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Abstract— The sound production from the Morávka fireball has been examined in detail making use of infrasound and seismic data. A detailed analysis of the production and propagation of sonic waves during the atmospheric entry of the Morávka meteoroid demonstrates that the acoustic energy was produced both by the hypersonic flight of the meteoroid (producing a cylindrical blast wave) and by individual fragmentation events of the meteoroid, which acted as small explosions (producing quasispherical shock waves). The deviation of the ray normals for the fragmentation events was found to be as much as 30° beyond that expected from a purely cylindrical line source blast. The main fragmentation of the bolide was confined to heights above 30 km with a possible maximum in acoustic energy production near 38 km. Seismic stations recorded both the direct arrival of the airwaves (the strongest signal) as well as air‐coupled P‐waves and Rayleigh waves (earlier signals). In addition, deep underground stations detected the seismic signature of the fireball. The seismic data alone permit reconstruction of the fireball trajectory to a precision on the order of a few degrees. The velocity of the meteoroid is much less well‐determined by these seismic data. The more distant infrasonic station detected 3 distinct signals from the fireball, identified as a thermospheric return, a stratospheric return, and an unusual mode propagating through the stratosphere horizontally and then leaking to the receiver.
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Abstract We investigate the possibility to constrain the evolution of the 2016 M7.8 Kaikoura earthquake evolution based on Global Positioning System signal‐derived ionospheric total electron content (TEC) perturbations, that represent plasma responses to infrasonic acoustic waves (IAWs) generated by surface motion. This earthquake exhibited unusual complexity and some first‐order aspects of its evolution remain unclear; for example, how and when the Papatea fault (PF) and the corresponding large surface deformation occurred. For various earthquake models, a seismic wave propagation code is used to simulate time‐dependent surface deformations, which then excite IAWs in a 3D compressible nonlinear atmospheric model, coupled with a 2D nonlinear multispecies ionospheric plasma dynamic model. Our preferred finite‐fault model reproduces the amplitudes, shapes, and time epochs of appearance of detected TEC perturbations well. Additionally, the incorporation of the PF, ruptured during the earthquake, results in the closest agreement between simulated and observed near‐zenith vertical TEC perturbations, whereas its absence shows significant discrepancy. This supports the hypothesis that the PF was ruptured during the Kaikoura earthquake. Furthermore, the IAWs and resulting ionospheric plasma disturbances contain additional information on the PF rupture progression, including the timing of initiation and propagation direction, indicating new opportunities to further constrain the PF rupture with low elevation angle “slant” TEC data. The results confirm the ability for TEC measurements to constrain evolutions of large crustal earthquakes to provide new insight beyond traditional seismic and geodetic data sets.
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