Experimental Study on the Features of Infrasonic Waves of Sandstone under Shear Load

The shear failure of rock is a major cause of rock slope instability and consequent landslides. To determine the forming mechanism of infrasonic waves during the loss of stability of sandstone slopes, experiments were carried out using a shear loading device and an infrasonic monitoring device. In the experiments, infrasonic wave events were identified, and the characteristic parameters of infrasonic waves were extracted to analyze the features of the infrasonic wave response during the shear failure of sandstone. The study results show that: (1) the whole process of shear failure was associated with infrasound events. A normalized energy cumulative coefficient of over 0.6 and a normalized infrasound rate of over 0.89 are the key time nodes for alarming landslide; (2) with an increase in sample size, the shear resistance of the sample increases logarithmically, the total energy of infrasound events increases exponentially, and the average dominant frequency of infrasound events decreases linearly; and (3) with an increase in axial pressure, the shear of the rock increases almost linearly, the number of infrasound events increases linearly, and the average dominant frequency of infrasound events increases exponentially. The research results provide important guidance for the dynamic monitoring and evaluation of the stability of sandstone slopes and can provide a theoretical reference for landslide alarming of sandstone slopes using infrasonic waves.

Evaluation of the Chemical Explosions Impact using Infrasound and InSAR Analysis

<p>Chemical explosions generate shockwaves which can be recorded at far distant with infrasound sensors. Infrasound propagation and energy of the explosion are main factors which control the infrasonic wave arrivals. In this study, a China explosion which happened on 22 March 2019, Biuret explosion on 4 August 2020, and the explosion of MOMO-2 rocket failure during the launching process will be investigated. The infrasound data sets of these explosions are extracted from IMS infrasound stations and KUT infrasound sensors which are distributed all over Japan.</p><p>The explosions had different propagation conditions which can be simulated using ray tracing and parabolic equation numerical methods, furthermore the transmission losses can be estimated in order to determine the yield energy in TNT-equivalent of each explosion, moreover the severe surface damages were identified by using InSAR techniques which can be classified according to the interferometric coherency.</p><p>In conclusion, the integration between the infrasound technique and InSAR showed the safety zone which should be taken in account for any chemical factories or rocket launch sites.</p>

Parameters of the Infrasonic Signal Generated in the Atmosphere by a Powerful Volcano Explosion

The purpose of this work is to represent the results of performing regression analysis to fit the distance and the amplitude of the infrasonic signal generated by the explosion of St. Helens volcano, and to estimate a few signal and atmospheric parameters. The pressure amplitude in the explosion wave generated at the beginning of St. Helens volcano eruption was measured at 13 stations in the 0.9 – 39-Mm distance range; based on these data, an attempt has been made to perform a regression analysis to fit amplitude and distance. The regression based on the assumption that the infrasound propagation takes place in a waveguide where it is subject to attenuation is determined to be the most preferable regression. Based on the observations of the shock from the St. Helens volcano eruption, the shock wave energy and mean power have been estimated to be ~1016 J and ~2.3 TW, respectively. Based on the observations of the amplitude and duration of the trains of the infrasonic wave generated by the St. Helens volcano eruption, the infrasonic wave energy and mean power have been estimated to be ~1016 J and ~2 TW, respectively. Both estimates are in good agreement, but they are significantly different from those found in the literature; the latter seem to be overestimated. From the regression expression obtained, the penetration depth of the infrasonic wave is obtained to be about 33 Mm, whereas at other stations this scale length is estimated to be close to 24 Mm. Based on the theoretical dependence of the attenuation coefficient due to atmospheric turbulence, the attenuation length of the infrasound wave has been estimated for infrasound with 10–300-s periods. For 20–300-s periods, this value has been shown to be significantly larger than the values determined from the observations. Other mechanisms for attenuating the infrasonic signal are discussed (the partial radiation of the infrasonic energy through and losses due to the reflection from the waveguide walls). At the same time, the wave attenuation due to their scattering by turbulent fluctuations can be significant for the periods smaller than 20–50 s, depending on the turbulence intensity. Comparison of the regression functions obtained with the corresponding regression expressions for other sources of infrasound waves propagating in the atmosphere has been made. Keywords: volcano eruption, infrasonic wave, shock wave, signal amplitude, regression, signal attenuation

A hollow inclusion self-similarity phononic crystal with an ultra-low-frequency bandgap

FEA method is applied in order to investigate the bandgaps of two-dimensional (2D) phononic crystals which are composed with self-similarity hollow inclusions. Transmission spectra together with dispersion relations and displacement fields have been studied with FEA in detail. The simultaneous mechanisms of Bragg scattering enable multiterm bandgaps to be unfolded by the structure that can be effectively shifted by changing the lattice constant, matrix density and degree of self similarity. The smallest bandgap is located in the infrasonic wave range. Our results verify these phononic crystals with self-similar hollow inclusion structure which can change the number, location and width of bandgaps.