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Seismic fault surfaces have complex geometries over a broad-scale range. The Hurst exponent (H) is an important parameter characterizing the complexity of fault geometries. This exponent of seismic faults has only been estimated at outcrops and from surface traces of large earthquakes. This is because geometry data of subsurface faults usually have large uncertainties and many gaps. This study examined the applicability of the lifting scheme, which is one of the wavelet transform methods, to estimate H of irregularly sampled geometry of subsurface faults. We analysed the surface geometry of the subducting oceanic plate at the Nankai trough, Japan, which is part of the fault plane of interplate earthquakes. The geometries of the subducting plate were estimated along six survey lines by integrating seismic refraction and reflection surveys. Two-way traveltimes of reflected waves from the plate surface, which were measured from the reflection survey data, were converted to depth using the velocity structure estimated by refraction survey. The intervals between sampled points were irregular because the reflected waves were obscured or invisible in some places. The Hurst exponents were estimated from the scale dependence of the wavelet coefficients that were derived by the lifting scheme without interpolation. Analyses of the synthetic data simulating the irregularly sampled plate geometries indicated that the lifting scheme yields stable but largely biased estimates of H , especially for small H (<0.5). We introduced the empirical bias correction to achieve an unbiased estimation of the exponent. The analysis of plate geometry at the Nankai trough was conducted at narrow-scale ranges with consideration for the accuracy of velocity structures. We may conclude that H of five survey lines across the trough axis is > 0.8, and that of a line along trough is > 0.7. These estimated exponents had large uncertainties due to analyses at narrow-scale ranges, but were close to the estimates in studies of the surface traces of large earthquakes. [ABSTRACT FROM AUTHOR]

At 04:14:45 UT on 2022 January 15, a powerful eruption of the submarine Hunga Tonga–Hunga Ha'apai volcano occurred at about 30 km south of the Ha'apai Islands in the Kingdom of Tonga (at −20.55° N, −175.39° E). This eruption caused atmospheric waves that spread worldwide. In this study, we investigate the the total electron content (TEC) variation over China using the BeiDou Navigation Satellite System. The particularly interesting feature of the data set compared to other ground-based TEC data is the exclusive use of the BeiDou geostationary satellites, which monitor the TEC variations for fixed ionospheric piercing points and can provide more accurate calculations of the travelling speed of the disturbance. For comparison, atmospheric pressure records were examined, which show that the Lamb wave passed by the same stations four times with a constant speed of 310 m s−1. However, the TEC results show that the ionospheric disturbances passing over China four times with different speeds within four days after the eruption, two travelling along the short-path direction and two along the long-path direction. The primary front of the first short-path event travels with a speed of 340 m s−1, which is higher than the Lamb wave. The faster speed suggests that the primary front cannot be fully attributed to the Lamb wave, and further studies need to explore its mechanism. The second short-path and first long-path events travel with speeds of 301 and 310 m s−1, respectively, close to the speed of the Lamb wave, and they may be caused by upward energy leakage during the propagation of the Lamb wave. The second long-path event travels with a speed of 264 m s−1, possibly induced by the gravity waves. [ABSTRACT FROM AUTHOR]

On 15 January 2022, a large eruption of the Hunga Tonga-Hunga Ha'apai volcano in Tonga triggered globally observed tsunami waves. While the first arrival in the observed wave trains is now widely known to be related to the atmospheric Lamb wave generated by the eruption, large later phases, whose amplitudes were comparable to the first ones, were also recorded. In this study, we estimated the source of the later phases based on the Vespa analysis and proposed a new numerical scheme to reproduce them. The Vespa analysis estimates the arrival time and incident angle of each signal by a slant-stack process using its theoretical traveltime. The Vespa analysis revealed that small atmospheric waves excited the large later tsunamis. For the numerical experiments, we used two types of synthetic methods: finite difference method and normal mode theory. We found that both a good atmospheric wave model and bathymetric effect were important to generate the atmospheric-induced tsunamis corresponding to the later phases. A hybrid method calculating tsunamis by the finite difference method with the atmospheric waves by the normal mode theory as the input successfully reproduced the observed records, particularly in amplitude over the entire records. [ABSTRACT FROM AUTHOR]

SUMMARY: The 15 January 2022 eruption of the Hunga–Tunga volcano generated a Lamb pressure wave propagating all over the globe and triggering a tsunami throughout the planet. A first atmospheric wave arrived 16 hr after the eruption on the French Mediterranean coasts and propagated southward. A second one originating from Africa was observed 4 hr later with an attenuated amplitude. The first wave can be roughly defined either by a N wave or a sinusoid signal with a period close to 50 min and an amplitude of 130 Pa. In the Mediterranean Sea, the tsunami was recorded by almost all standard coastal tide gauges or pressure gauges. The French tide gauge stations recorded water waves with amplitudes ranging from a few centimetres to 10 cm and with periods ranging from 10 min to 1 hr. Numerical simulation of the tsunami is performed by the operational code Taitoko for different atmospheric sources. Non-linear shallow water equations are solved by a finite-difference method, using the nested multigrid approach. The tsunami is generated by calculating analytically the atmospheric pressure gradient in the momentum equations. Comparisons of time-series between numerical solutions and records are satisfactory for most tide-gauges along the French Mediterranean coast. Sensitivity analysis on the atmospheric source and on the resolution is performed. For most tide-gauge stations, numerical results show that the wave forms depend first on local resonance phenomena. [ABSTRACT FROM AUTHOR]

The massive explosive eruption of the Hunga volcano on 15 January 2022 generated atmospheric waves that were recorded around the globe and affected the ionosphere. The paper focuses on observations of atmospheric waves in the troposphere and ionosphere in Europe, however, a comparison with observations in East Asia, South Africa and South America is also provided. Unlike most recent studies of waves in the ionosphere based on the detection of changes in the total electron content, this study builds on detection of ionospheric motions at specific altitudes using continuous Doppler sounding. In addition, much attention is paid to long-period infrasound (periods longer than ∼50 s), which in Europe is observed simultaneously in the troposphere and ionosphere about an hour after the arrival of the first horizontally propagating pressure pulse (Lamb wave). It is shown that the long-period infrasound propagated approximately along the shorter great circle path, similar to the previously detected pressure pulse in the troposphere. It is suggested that the infrasound propagated in the ionosphere probably due to imperfect refraction in the lower thermosphere. The observation of infrasound in the ionosphere at such large distances from the source (over 16 000 km) is rare and differs from ionospheric infrasound detected at large distances from the epicenters of strong earthquakes, because in the latter case the infrasound is generated locally by seismic waves. An unusually large traveling ionospheric disturbance (TID) observed in Europe and associated with the pressure pulse from the Hunga eruption is also discussed. Doppler sounders in East Asia, South Africa and South America did not record such a significant TID. However, TIDs were observed in East Asia around times when Lamb waves passed the magnetically conjugate points. A probable observation of wave in the mesopause region in Europe approximately 25 min after the arrival of pressure pulse in the troposphere using a 23.4 kHz signal from a transmitter 557 km away and a coincident pulse in electric field data are also discussed. [ABSTRACT FROM AUTHOR]

We report a mode of ionospheric resonance induced by the 2022 January 15, Hunga Tonga–Hunga–Ha'apai volcanic eruption, captured globally through ground-based Global Navigation Satellite Systems networks. In the near-field region, we observe a strong ionospheric disturbance in the total electron content, including contributions from acoustic and gravity waves. In contrast, propagation of gravity waves, seismic airwaves diffracted by topographic barriers and/or atmospheric Lamb waves can be documented for far-field ionospheric disturbances. Specifically, the atmospheric wave propagation towards the Hawaii Islands involved three distinct modes of ionospheric perturbation through Rayleigh, gravity and atmospheric Lamb waves. Further, we also noted that the peak-to-peak amplitude of the disturbance reached ∼ 8.7 per cent of the background electrons, which is significantly higher than the recent volcanic explosions in the Japanese Islands and the 2020 chemical explosion in Beirut. The ionospheric total electron content perturbations can provide important information about the volcanic source, hence they could be useful as a measure of eruption intensity and for real-time hazard monitoring. [ABSTRACT FROM AUTHOR]

The Hunga Tonga-Hunga Ha'apai volcano eruption resulted in propagation of tsunamis globally. Atmospheric pressure disturbances and tsunamis were recorded in Lingding Bay, China, situated more than 9000 km from the volcano. We studied the features of tsunamis in Lingding Bay and its surrounding areas by using records from tide gauges and meteorological stations. Lamb waves were observed in the bay approximately 8, 44 and 80 hr after the volcanic eruption. The first and second tsunami waves arrived approximately 11 and 45–47 hr following the eruption, respectively, indicating consistency with the arrival time of Lamb waves. In addition, wavelet and Fourier analyses were applied to the sea level records to investigate the frequency characteristics. The ratio of the tsunami spectra to the background spectra for two tsunami waves was calculated as the source spectra. The source spectra of two tsunami waves were mostly of the same shape, with dominant periods of ∼17 and ∼46 min. Our results provide information for theoretical investigation of the Tonga tsunami event. More efforts should be devoted to relevant research on the generating mechanism and early warning of tsunamis from non-seismic origins. [ABSTRACT FROM AUTHOR]

An analytically based method is proposed to simulate the acoustic-gravity waves in the horizontally stratified atmosphere-Earth structure generated by a point force on the Earth's surface. The method solves the linear momentum, continuity and adiabaticity equations in the atmosphere and elastodynamic equations in the solid Earth in the frequency–wavenumber domain. The time-domain waveforms are obtained by wavenumber integration and fast Fourier transform with respect to the frequency. Numerical simulations are conducted to investigate the properties of the acoustic-gravity waves, including both the high-frequency acoustic-mode waves and low-frequency gravity-mode waves. Simulations of the high-frequency responses show that disturbances in the atmosphere with three apparent horizontal velocities can be identified. They are, namely, the direct acoustic-mode wave generated by source travelling with the sound speed, the head wave generated by the seismic P -wave travelling with apparent horizontal speed identical to the P velocity, and the head wave generated by the Rayleigh wave with a horizontal speed same to the Rayleigh wave velocity. Simulations of the low-frequency responses show that the gravity-mode wave and Lamb wave can be identified. The gravity-mode wave travels with a speed lower than the sound seed and does not reach everywhere, especially the area directly above the source. The Lamb wave travels along the Earth surface with a speed of about 310 m s–1 and its energy decays with the altitude. We also apply our method to explaining the Doppler sounding data observed in Taiwan area during the 2011 Tohoku M 9 earthquake, and find good agreement between the predicted signals and observed data in the arrival time and wave envelope associated with the Rayleigh wave. [ABSTRACT FROM AUTHOR]

Propagation of Lamb waves has been studied in an infinite plate of finite thickness and composed of elastic–plastic material containing void pores. The plastic deformation in the plate material is considered through a single-plane and direction. Assuming a linear relation between the elastic and plastic parts of the change in void volume fraction and using the stress-free boundary surfaces of the plate, the dispersion relations corresponding to the symmetric and antisymmetric vibrations with respect to the mid-plane of the plate are derived. The corresponding dispersion relations of Lamb modes in the elastic–plastic plate have been reduced by neglecting the presence of voids. Some earlier known results are recovered from the present formulation under particular cases. The behaviour of symmetric and antisymmetric family of Lamb modes are depicted pictorially against the frequency, slip-angle, thickness of the plate and void parameters in a specific plate material. It is found that the plasticity and the presence of the voids in the plate material affect the propagation of Lamb modes. In particular, at the slip-angle |$45^o$|⁠ , the |$S_0$| - and |$A_0$| - modes exhibit symmetry, but |$S_0$| is bell shaped and |$A_0$| is parabolic. [ABSTRACT FROM AUTHOR]

We present in this work an ultrasonic imaging technique based on wavefield cross-correlation that has potential for high-resolution inspecting of plates and plate-like structures. A curved transmit/receive array setup is used for acquiring wide-aperture waveform data beneficial for applying the presented imaging condition. An additional dispersion analysis using waveform data received by a linear array allows one to reveal the excited guided wave modes and possibly determine the shear wave velocity as an input parameter in the 3D wavefield simulation. Using synthetic but realistic data generated by realistic 3D simulations, we demonstrate the invariance of the time reversal process and the capability of the presented imaging approach for ultrasonic testing based on Lamb waves. In addition to the ability to localise and size multiple defects simultaneously, this imaging approach does not require baseline data and involves only minimal waveform data pre-processing. [ABSTRACT FROM AUTHOR]

Lamb production in tropical areas is conducted under heat stress in extensive grazing conditions of naturalized pastures (NP). The average daily gain (ADG) and yields of hot (HCY) and cold (CCY) carcass, wholesale cuts (WSC); neck (N), shoulder (SL), ribs 5-12 (RIB), loin (LN) and leg (LG), and detail cuts (DTC); shoulder chops (SCH), french chops (FCH), ribs (RS), back leg (BL) and shanks (SH) of 12 lambs (X = 19.4 kg) rotationally grazed (3 d occupation and 24 d resting period) for 154 or 238 d were determined. The Lambs grazed >8 h NP, grass hay and water were offered ad libitum, 150 g/d of a supplement (12% CP), and mineral blocks. Weekly weights were used to determine ADG. Lambs were slaughtered at 22 (SW1) or 35 kg (SM2) to determine HCY and CCY, and WSC and DTC yield as % of cold carcass weight. Performance data was analyzed as a randomized experimental (CRD) design over time. Carcass and cut yields data were analyzed as a CRD with 6 replicates per treatment. Lambs fed during 238-d had similar ADG than those fed 154-d (68.14 vs.47.74 g/d). SW1 and SW2 had similar percentages of HCY (35.21 vs. 38.14) and CCY (34.48 vs. 37.40). The WSC as % of cold carcass weight, N (6.43 vs. 7.06), SL (29.95 vs. 30.20), RIB (16.10 vs. 16.95), LN (10.84 vs. 11.33) and LG (36.51 vs. 34.44) were similar for SW1 and SW2. Yield of SCH and SH was lower (P < 0.05) for SW1 (15.80 and 8.11) than SW2 (23.00 and 9.11), but FCH (8.49 vs. 8.57), RS (6.89 vs. 7.00) and BL (36.52 vs 34.45) were similar. In summary, lambs slaughtered at 35 kg improved the retail cut yield, but did not influence ADG, HCY, CCY, and WCY compared to lighter lambs. [ABSTRACT FROM AUTHOR]