Amplification Of Waves Research Articles

An Appraisal of Ground Failure and Hydrogeological Changes Associated with the 28 April 2021 Mw 6 Sonitpur Earthquake, Assam, India, Using Field Evidences and InSAR Measurements

Abstract Widespread damage and coseismic ground disturbances are generally associated with large magnitude and/or shallow focus earthquakes. Surprisingly, a deep focus (34 km), moderate magnitude earthquake (Mw 6) occurred near the Kopili fault zone in Sonitpur district, Assam, India, on 28 April 2021 and created intense ground shaking and extensive damage along the Brahmaputra Valley. We undertook a field survey within a day after the earthquake and carried out Interferometric Synthetic Aperture Radar (InSAR) analysis to map any coseismic ground deformation features. Our field survey revealed extensive liquefaction features and several coseismic secondary ground cracks along the alluvial tracts of the Brahmaputra River system. InSAR analysis revealed a sinistral slip up to ∼60 mm along a north-northwest–south-southeast-oriented previously unmapped lineament or fault. Field investigations revealed coseismic hydrological changes including a sudden rise and fall in the water level by 0.3–0.5 m followed by the injection of sand materials up to a thickness of 1.25 m in dug wells and the appearance of water in seasonally dried river channels and ponds. Interferometric coherence analysis during pre-, co-, and postseismic periods further confirmed the coseismic surge in water at five major tributary rivers of the Brahmaputra River. We speculate that the pressure difference at the shallow unconfined aquifer system of the mountain-front alluvial fan induced by coseismic stresses must have caused channeling of groundwater to the rivers and the contemporaneous water level fluctuations in wells. Amplification of seismic waves at the thick, unconsolidated sedimentary strata of the Brahmaputra Valley could have enhanced the extensive damage due to the 2021 Sonitpur earthquake. The present study has implications in estimating damage potential along the Brahmaputra Valley for future earthquakes.

Ambient high-frequency seismic surface waves in the firn column of central west Antarctica

AbstractFirn is the pervasive surface material across Antarctica, and its structures reflect its formation and history in response to environmental perturbations. In addition to the role of firn in thermally isolating underlying glacial ice, it defines near-surface elastic and density structure and strongly influences high-frequency (> 5 Hz) seismic phenomena observed near the surface. We investigate high-frequency seismic data collected with an array of seismographs deployed on the West Antarctic Ice Sheet (WAIS) near WAIS Divide camp in January 2019. Cross-correlations of anthropogenic noise originating from the approximately 5 km-distant camp were constructed using a 1 km-diameter circular array of 22 seismographs. We distinguish three Rayleigh (elastic surface) wave modes at frequencies up to 50 Hz that exhibit systematic spatially varying particle motion characteristics. The horizontal-to-vertical ratio for the second mode shows a spatial pattern of peak frequencies that matches particle motion transitions for both the fundamental and second Rayleigh modes. This pattern is further evident in the appearance of narrow band spectral peaks. We find that shallow lateral structural variations are consistent with these observations, and model spectral peaks as Rayleigh wave amplifications within similarly scaled shallow basin-like structures delineated by the strong velocity and density gradients typical of Antarctic firn.

Parsimonious Velocity Inversion Applied to the Los Angeles Basin, CA

AbstractThe proliferation of dense arrays promises to improve our ability to image geological structures at the scales necessary for accurate assessment of seismic hazard. However, combining the resulting local high‐resolution tomography with existing regional models presents an ongoing challenge. We developed a framework based on the level‐set method that infers where local data provide meaningful constraints beyond those found in regional models ‐ for example the Community Velocity Models (CVMs) of southern California. This technique defines a volume within which updates are made to a reference CVM, with the boundary of the volume being part of the inversion rather than explicitly defined. By penalizing the complexity of the boundary, a minimal update that sufficiently explains the data is achieved. To test this framework, we use data from the Community Seismic Network, a dense permanent urban deployment. We inverted Love wave dispersion and amplification data, from the Mw 6.4 and 7.1 2019 Ridgecrest earthquakes. We invert for an update to CVM‐S4.26 using the Tikhonov Ensemble Sampling scheme, a highly efficient derivative‐free approximate Bayesian method. We find the data are best explained by a deepening of the Los Angeles Basin with its deepest part south of downtown Los Angeles, along with a steeper northeastern basin wall. This result offers new progress toward the parsimonious incorporation of detailed local basin models within regional reference models utilizing an objective framework and highlights the importance of accurate basin models when accounting for the amplification of surface waves in the high‐rise building response band.

A dissection of the topographic effects from Eurasia and North America on the isentropic meridional mass circulation in Northern Winter

The topographic dynamical effect from Eurasia (EA_Topo) and North America (NA_Topo) on the winter isentropic meridional mass circulation (IMMC) is investigated using the WACCM. The independent effect of EA_Topo and that of NA_Topo, with the former much stronger, are both to strengthen the IMMC that is composed of the lower equatorward cold air branch (CB) and the upper poleward warm air branch in the extratropical tropopshere (WB_TR) and stratosphere (WB_ST). Further investigation of the individual contributions from changes in stationary vs. transient and zonal-mean flow vs. waves reveals that, due to the topography-forced mass redistribution, changes in the low-level meridional pressure gradient force a zonal-mean counter-clockwise/clockwise meridional cell in the southern/northern side of topography. This weakens/strengthens the IMMC south/north of 30° N from the troposphere to lower stratosphere, acting as a dominant contributor to the IMMC changes south of 50° N. Meanwhile, the EA/NA_Topo-forced amplification of stationary waves constructively interacts with those determined by land-sea contrast, making the dominant/minor contributions to the strengthening of CB and WB_TR north of 50° N. The related increase in the upward wave propagation further dominates the WB_ST strengthening in the subpolar region. Meanwhile, transient eddy activities are depressed by EA/NA_Topo along with the weakened background westerly, which partly-offset/dominate-over the contribution from stationary flow in midlatitudes and subpolar region. The coexistence of the other topography (NA/EA_Topo) yields destructive mutual interferrence, which can weaken/offset the independent-EA/NA_Topo-forced meridional mass transport mainly via changing the zonal-mean as well as the downstream wave pattern of mass and meridional wind.

Numerical Modelling of Underground Water Pipelines exposed to Seismic Loading

The essential factor that must get the interest by the engineers during the primary design stage of underground pipes is understanding mechanism of damage during earthquakes. The attention during design period increased due to the increment of seismic catastrophes throughout the few past decades. Therefore, finite element procedure was used for studying the seismic performance of buried pipes. PLAXIS-2D program was using for simulating the seismic performance of buried pipes using earthquake motion of single frequency. The response of both seismic vertical displacement, and acceleration of the buried pipe were simulated. The experiments of shaking table for two models of buried pipe in dry case that surrounded with sand and gravel were compared with numerical simulation results. According to the obtained results, the amplification of seismic wave raised considerably from the buried pipe base to the pipe crown, the biggest amplification occurred in the highest point of the pipe model. It can be noticed that Plaxis-2D software provides an accurate method for the prediction of seismic behaviour of buried pipe due to the obvious compatibility between the results of experiments and numerical simulation.

Numerical Simulation of Wave Interaction With a Pair of Fixed Large Tandem Cylinders Subjected to Regular, Non-Breaking Waves

Abstract This paper presents the application of a two-phase computational fluid dynamics (CFD) model to carry out a detailed investigation of the nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the unsteady Reynolds-averaged-Navier-Stokes/volume of fluid (VOF) model based on the openfoam framework combined with the olaFlow toolbox for wave generation and absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data for a single cylinder. Future, the given simulations are conducted for different center-to-center distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern, and consequently, high wave amplification harmonics around cylinders are apparent.

PredictingVpand constrained modulus reduction curve based onVsand shear modulus reduction curve in accordance with poroelastic theory

The compression wave velocity (Vp) of sediments plays a key role in seismic wave amplification of vertical motion and is required in site response analysis. However, such information is usually lacking during field exploration (e.g. the surface wave method) because only shear wave velocity (Vs) is obtained. This aim of this study is to predict Vpbased on Vsempirically and theoretically, particularly focusing on saturated conditions. The empirical approach is to establish the Vpcorrelation dependency on Poisson's ratio and Vs, and the theoretical approach is based on poroelastic theory that accounts for the interaction between fluid and soil skeleton. The engineering geological database for the Taiwan strong motion instrumentation program and the Kiban Kyoshin network database in Japan are adopted to establish an empirical model and validate poroelastic theory. The validated poroelastic approach is used to develop a constrained modulus reduction curve dependency on the porosity, Vs, Poisson's ratio and degree of saturation with a shear modulus reduction curve. The proposed approach can be used to develop generic Vpprofiles and constrained modulus reduction curves for the site response to vertical motion given a site-specific Vsprofile.

Microwave Space-Time-Modulated Metasurfaces

Over the past decade, static metasurfaces have proved to be low-profile and efficient apparatuses for transformation of electromagnetic waves. However, such metasurfaces are restricted by their reciprocal and time- and frequency-invariant responses. To overcome these restrictions, space-time-modulated metasurfaces have recently been introduced for versatile, reciprocal/nonreciprocal, and frequency translation of electromagnetic waves. These are capable of changing both the momentum and energy of the incident wave and provide functionalities that are far beyond the capabilities of conventional static and reciprocal metasurfaces. This Perspective provides a discussion on the unique functionalities of a microwave space-time-modulated metasurface. In particular, we review various techniques that have been recently used for the realization of metasurfaces introducing spatiotemporal decomposition, scattering and diffraction, digital coding, nonreciprocal transmission, serrodyne frequency translation, pure frequency conversion, parametric wave amplification, and multifunctional operations. Although the paper focuses on microwave space-time metasurfaces, the described concepts can inspire realization of their optical counterparts.

Mesoscale Gravity Waves and Midlatitude Weather: A Tribute to Fuqing Zhang

Abstract Over the course of his career, Fuqing Zhang drew vital new insights into the dynamics of meteorologically significant mesoscale gravity waves (MGWs), including their generation by unbalanced jet streaks, their interaction with fronts and organized precipitation, and their importance in midlatitude weather and predictability. Zhang was the first to deeply examine “spontaneous balance adjustment”—the process by which MGWs are continuously emitted as baroclinic growth drives the upper-level flow out of balance. Through his pioneering numerical model investigation of the large-amplitude MGW event of 4 January 1994, he additionally demonstrated the critical role of MGW–moist convection interaction in wave amplification. Zhang’s curiosity-turned-passion in atmospheric science covered a vast range of topics and led to the birth of new branches of research in mesoscale meteorology and numerical weather prediction. Yet, it was his earliest studies into midlatitude MGWs and their significant impacts on hazardous weather that first inspired him. Such MGWs serve as the focus of this review, wherein we seek to pay tribute to his groundbreaking contributions, review our current understanding, and highlight critical open science issues. Chief among such issues is the nature of MGW amplification through feedback with moist convection, which continues to elude a complete understanding. The pressing nature of this subject is underscored by the continued failure of operational numerical forecast models to adequately predict most large-amplitude MGW events. Further research into such issues therefore presents a valuable opportunity to improve the understanding and forecasting of this high-impact weather phenomenon, and in turn, to preserve the spirit of Zhang’s dedication to this subject.

Ray-tracing simulations of whistler-mode wave propagation in different rescaled dipole magnetic fields

Kinetic simulation is a powerful tool to study the excitation and propagation of whistler-mode waves in the Earth’s inner magnetosphere. This method typically applies a scaled-down dipole magnetic field to save computational time. However, it remains unknown whether whistler wave propagation in the scaled-down dipole field is consistent with that in the realistic dipole field. In this work, we develop a ray-tracing code with a scalable dipole magnetic field to address this concern. The simulation results show that parallel whistler waves at different frequencies gradually become oblique after leaving the equator and propagate in different raypaths in a dipole magnetic field. During their propagation, the higher frequency waves tend to have larger wave normal angles at the same latitude. Compared with the wave propagation in a realistic dipole field, the wave raypath and wave normal remain the same, whereas the wave amplification or attenuation is smaller because of the shorter propagation time in a scaled-down dipole field. Our study provides significant guidance for kinetic simulations of whistler-mode waves.

Numerical study of the effect of the corrugated baffle on the acoustic characteristics of the combustion chamber

Combustion instability caused by the amplification of sound waves is called acoustic or high-frequency instability, which can cause severe damage to the system. Adding baffles is one of the methods of passive instability control. Depending on the geometry of the chamber and the type of application, different baffles are used. In this research, the effect of the longitudinal corrugated baffle on the acoustic characteristics of the combustion chamber is investigated numerically. The quality of each baffle configuration is determined by examining their influence on the essential parameters such as natural frequency shift and damping factor. Modal and harmonic analyses for the acoustic field are conducted to investigate the effect of baffles installed in the combustion chamber. According to the obtained results, the addition of baffle shifts resonant frequencies. In other words, a combustor with baffles is more effective in controlling the instabilities than that without baffles. In addition, it increases the damping factor in the first–second circumferential (tangential) modes, making the system more stable. Also, a quantitative assessment of the acoustics by adding baffles shows that combustion chamber finds a better condition from stability point of view, and the bandwidth increase affects the combustion stability.

A Study on the Development of Data COMMUCATION MODULE within Construction

Purpose: As for the safety related technologies in the field of construction and site, and in order to implement an optimal communication transmission and reception related environment, an environment which can help prevent a loss of data ought to be structured. Hence, the purpose of this paper is to identify and remove the noise elements which cause the loss of data via empirical experiments, examine the elements which can help improve communication performance within the range of radio regulations, and develop the communication module appropriate for the relevant environment. Method: The validation methodology of this paper is as follows. A comparison validation test of the customized communication environment compared to the existing communication equipment related application environment, a validation test as to whether a loss of data occurs between the AR devices, a correlation validation test between the occurrence of a loss of data due to a noise increase, a validation and development methodology for identifying the correlation between the transmission distance and the amount of data transmission and reception related variation via the validation test for the impact of data transmission are presented. Results: Since the data transmission and reception volume relatively increases in the customized communication related environment compared to the existing communication equipment related application environment for a certain period of time, it is apparent that the data transmission and reception volume between the AR devices is reduced by causing a network delay due to the overload of network equipment. Hence, it is expected that, in order to address such problems, a communication module appropriate for the environment will be developed, and the noise will be reduced via the validation. Conclusion: As it is necessary to derive the customized values for the communication equipment applicable for the construction site through this study, it is necessary to calculate the quantitative values for the improvement of the data transmission and reception volume during the radio wave amplification, and it has also been derived that it is necessary to derive the quantitative values between a loss of data due to the generation of noise. In the future studies, it is considered that a comparative validation test will be needed in an indoor and outdoor test environment in which an interference from the existing communication environment occurs and an anechoic testing environment in which an interference does not occur whatsoever from the existing communication environment.

Wave amplification caused by Bragg resonance on parabolic-type topography

Inspired by the focusing principle of a parabolic-type mirror and the wave Bragg resonance, a parabolic-type spatial layout with a Bragg bottom is proposed, which can significantly amplify wave height. The wave propagation characteristics on the parabolic-type topography were numerically investigated using a developed numerical model based on the High-Order Spectral (HOS) method. The amplification properties of the wave height on the proposed parabolic topography with a Bragg bottom were systematically analyzed considering different ripple heights, ripple numbers, topographic widths and focal lengths. The results show that the focusing effect of wave height increases with the increase of the ripple height, ripple number and topographic width. However, when the ripple number and topographic width are bigger than certain constants, their effect on wave focusing becomes insignificant. Compared with the traditional parallel-type layout, the ripple number of the proposed parabolic-type layout can be reduced to one-fifth to achieve the same amplified effect of the parallel layout with the same ripple height. Moreover, the focus length also influences the wave focusing by changing the wave collection angle. From the presented studies, the optimal collection angle of the parabolic-type layout is approximately in the range of 82°–115°.

Terahertz wave amplification by a laser-modulated relativistic electron beam

Generation of tunable terahertz radiation based on the interaction of a frequency-chirped low power terahertz wave with a relativistic electron beam is proposed. The electron beam is first modulated temporally due to the ponderomotive force induced by the beat wave of two copropagating intense laser beams of slightly different frequencies. Then the electron beam interacts with a low-amplitude driver wave at terahertz frequency with a linear frequency chirping. A nonlinear transverse current density is driven that emits terahertz radiation at an up-shifted frequency with a relatively enhanced amplitude. The modulation process is analyzed theoretically by a complete set of fluid equations and considering the effects of both the electrons space-charge potential and the beat wave ponderomotive force. The initial density and energy of the electron beam are both optimized in order to improve the terahertz amplification process. The effect of the driver's frequency chirping, as well as the effects of the initial electron beam density and energy on the emitted terahertz radiation are investigated numerically. It is shown that the frequency chirping of the driver wave plays a key role in terahertz amplification. It is shown that there is an optimum chirp value for which the terahertz radiation is amplified significantly compared with the case without chirping. Moreover, transverse effects of the laser beams and the driver wave on the emitted terahertz radiation are also investigated.

Coseismic Stability Assessment of a Damaged Underground Ammunition Storage Chamber Through Ambient Vibration Recordings and Numerical Modelling

In the past decade, ambient vibration measurements found numerous applications on unstable rock slopes and developed into a powerful tool for site characterization of slope instabilities. In this study, for the first time ambient vibration measurements were applied to a rock mass strongly disturbed and damaged by subsurface explosions. The site above the ammunition storage chamber at Mitholz (Switzerland) is especially interesting because the subsurface geology below the seismic array is well known, including the location of the caverns, and the degree of degradation caused by the subsurface explosions in 1947 of around 40 t TNT of ammunition. Measurement data were analyzed using current state-of-the-art seismic single-station and array methods, focusing on surface-wave dispersion analysis, wave field polarization, wave amplification using site-to-reference spectral ratios and analysis of normal mode behavior. The results allow for calibrating the elastic properties of a 2D numerical rock mechanical model which was used to simulate the stability of the disturbed rock mass during seismic loading. Therefore, ambient vibration measurements can contribute not only to a better understanding of the subsurface, but also for the assessment of earthquake risk.

The Fine‐Scale Structure of Long Beach, California, and Its Impact on Ground Motion Acceleration

AbstractThe metropolitan Los Angeles region represents a zone of high‐seismic risk due to its proximity to several fault systems, including the San Andreas fault. Adding to this problem is the fact that Los Angeles and its surrounding cities are built on top of soft sediments that tend to trap and amplify seismic waves generated by earthquakes. In this study, we use three dense petroleum industry surveys deployed in a 16 × 16‐km area at Long Beach, California, to produce a high‐resolution model of the top kilometer of the crust and investigate the influence of its structural variations on the amplification of seismic waves. Our velocity estimates reveal substantial lateral contrasts and correlate remarkably well with the geological background of the area, illuminating features such as the Newport‐Inglewood fault, the Silverado aquifer, and the San Gabriel river. We then use computational modeling to show that the presence of these small‐scale structures have a clear impact on the intensity of the expected shaking, and can cause ground‐motion motion acceleration to change by several factors over a subkilometer horizontal scale. These results shed light onto the scale of variations that can be expected in this type of tectonic settings and highlight the importance of resolution in modern‐day seismic hazard estimates.

Supersonic jet by blast wave focusing

A supersonic jet of Mach number M = 4.5 in air is produced experimentally at the apex of a miniature 150 × 50 × 5 mm converging section with a 2 × 5 mm opening by the principle of blast wave amplification through focusing. An initial plane blast wave of M = 2.4 in the convergence section is generated by the exploding wire technique. The profile of the convergence section is specially tailored to smoothly transform a plane blast wave into a perfectly cylindrical arc, imploding at the apex of the section. The cylindrical form of the imploding shock delivers maximum shock amplification in the two-dimensional test section and maximum subsequent jet flow velocity behind the shock front. Blast wave propagation in the convergence chamber as well as jet generation through a 2 mm opening at the apex into the adjacent exhaust chamber is optically captured by a high-speed camera using the shadowgraph method. Visualizing the flow provided a distinct advantage not only for obtaining detailed information on the flow characteristics but also for validating the numerical scheme which further enhanced the analysis. Experimental images together with the numerical analysis deliver detailed information on the blast wave propagation and focusing as well as subsequent jet initiation and development. One of the main advantages of the described method apart from being simple and robust is the effective focusing of low initial input energy levels of just around 500 Joules, resulting in production of supersonic jets in a small confined chamber.

Local magnitude calibration of seismic events in the West Rand, Far West Rand, and Klerksdorp-Orkney-Stilfontein-Hartebeesfontein gold mining areas

Richter magnitudes for seismic events were calibrated for use as a Local magnitude scale in the West Rand (WR), Far West Rand (FWR), and Klerksdorp-Orkney-Stilfontein-Hartebeesfontein (KOSH) gold mining areas. Richter magnitudes are currently calculated from seismograms recorded by local surface cluster networks using tabulated calibration values for Southern California, published in 1958. The Richter (1958) model is incorrect for distances of less than 30 km and should be applied only to crustal earthquakes in regions with similar attenuation properties to those of Southern California. When compared to the South African National Seismograph Network (SANSN), the cluster networks, on average, overestimate seismic event magnitudes by approximately 0.1 of a magnitude unit. A calibrated Local magnitude scale was derived by means of a multiple regression analysis between the Local magnitudes reported by the SANSN and the largest zero-to-peak trace amplitudes measured on the cluster network horizontal seismograms, after modelling the attenuation of the seismic waves as these progress from the epicentre to the station position. Magnitudes reported by individual stations for the same event show a significant scatter around the average magnitude owing to the near-surface amplifications of the seismic waves at the recordings sites. Average magnitude should be estimated using as many magnitudes of individual stations as possible to ensure an accurate estimate. Larger event magnitudes should be compared with those recorded by the SANSN.

Gauge field theory vacuum and cosmological inflation without scalar field

We derive the quantum energy–momentum tensor and the corresponding quantum equation of state for gauge field theory using the effective Lagrangian approach. The energy–momentum tensor has a term proportional to the space–time metric and provides a finite non-diverging contribution to the effective cosmological term. This allows to investigate the influence of the gauge field theory vacuum polarisation on the evolution of Friedmann cosmology, inflation and primordial gravitational waves. The Type I–IV solutions of the Friedmann equations induced by the gauge field theory vacuum polarisation provide an alternative inflationary mechanism and a possibility for late-time acceleration. The Type II solution of the Friedmann equations generates the initial exponential expansion of the universe of finite duration and the Type IV solution demonstrates late-time acceleration. The solutions fulfil the necessary conditions for the amplification of primordial gravitational waves.

Ground accelerations and empirical site classification through H/V response spectral ratio (HVRSR) using historical records from the strong motion network of the Aburrá Valley, Colombia

Using data from the strong motion network of the Aburrá Valley in Colombia, consisting of approximately 24 years of records, we studied the seismic response of 30 sites in the Metropolitan area of the city of Medellín and surrounding municipalities. The network recorded over 240 earthquakes since 1996, with magnitudes between 1.7 and 6.7. The strong motion records indicate a maximum Peak Ground Acceleration (PGA) of 0.05 g (55 gals). We computed the damped 5% response spectra to estimate the soil's natural periods at each site, using the Horizontal-to-Vertical Response Spectral Ratio (HVRSR). The fundamental periods vary from ∼0.1 s to ∼0.5 s, allowing us to perform a first-order characterization of soil rigidity as well as the classification of the soils in five categories. This classification shows a reasonable relationship with the local geology in the Aburrá Valley, which mainly consists of a metamorphic basement, igneous intrusions, and slope and alluvial deposits, with a highly variable degree of mechanical and chemical weathering. The relatively short fundamental periods indicate an absence of soft soils among the station sites, often associated with the largest amplification of seismic waves. The classes identified show spectral amplifications on natural periods, relative to hard-rock, with factors between 2 and 4.5.