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Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, М W =8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017. The distribution of seismicity with depth was studied in detail. The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion. The latter mechanism can also explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones. In general, the typical character of subduction deformations has a number of features in the Middle America Trench. The predominance of shortening by horizontal components and elongation by vertical ones at depths up to 35 km is replaced by the transitional type with mosaic distribution of deformations of different signs in the depth range of 36–70 km. Even lower, in the depth range of 70–105 km, the type of deformation changes to the opposite with respect to the upper horizon. The Chiapas earthquake occurred on the border of regions with different types of deformation, which indicates softening of the block’s medium to the west of the hypocenter and its hardening to the east. Such a state of the lithospheric medium may indicate the presence of a deformation shadow zone in the Chiapas earthquake preparation area.

This paper presents an atmospheric propagation model, based on ray acoustics, that accounts for realistic weather conditions in the evaluation of the noise footprint of an aircraft. Noise sources, obtained using the Ffowcs Williams and Hawkings acoustic analogy applied to scale-resolved flow simulation data, are stored on a hemisphere surrounding the vehicle. These noise sources are propagated using a propagation model that takes into account the vertical variability of air temperature and wind velocity. The electric vertical takeoff and landing aircraft, presented by Casalino, van der Velden, and Romani [(2019). in Proceedings of the AIAA Scitech 2019 Forum, January 7-11, San Diego, CA, pp. 1834-1851], is used as a case study; noise footprints, obtained considering various vertically varying temperature and wind velocity distributions, are compared. It is shown that weather conditions in the acoustic wave propagation can contribute to mismatch up to 4 dBA in the illuminated zone and a significant drop in the refractive shadow zone caused by the vertical air temperature and wind velocity gradients. This work constitutes the first accomplishment in including realistic atmospheric effects in aircraft community noise prediction based on scale-resolved flow simulations.

Scale-model tank experiments offer a controlled environment in which to make underwater acoustic propagation measurements that can provide high-quality data for comparison with numerical models. This paper presents results from a scale model experiment for a translationally invariant wedge with a 10° slope fabricated from closed-cell polyurethane foam to investigate three-dimensional (3-D) propagation effects. A computer controlled positioning system accurately located a receiving hydrophone in 3-D space to create a dense field of synthetic vertical line arrays, which are subsequently used to mode filter the measured pressure field. The resulting mode amplitudes show the modal propagation zone, the modal shadow zone, and the classical intra-mode interference pattern resulting from rays launched up and along the slope. The observed features of the measured data are compared to three different propagation models: an exact, closed-form solution for a point source in wedge with pressure release boundaries, a 3-D ray trace model, and an adiabatic model. Examination of the mode amplitudes produced by the models reveals how the effects of vertical mode coupling can be observed in the measured data.

The aircraft deicing and detection tasks are complicated by the revealed existence of a shadow zone behind the wings, which contains no droplets due to the wing shielding effect. The effects of thi...

The Red-Blue-Green Light Emitting Diode (RGB-LED) light used in the static lift net can manipulate fish behavior to attract, approach and be concentrated in the lighting area. The purpose of this study is to determine the use of the RGB-LED light intensity with pulse width modulation PWM) value for gathering fish and changing patterns of schooling fish’s movement. Seven treatments with changes in PWM values were the initial conditions, 250, 195, 145, 95 20 and 5 PWM. The methods were by using Hydro-acoustic sonar 360o and ImageJ analysis used to determine the schooling fish’s area in horizontal and vertical by dividing the center zone, main zone, influence zone, and shadow zone. Results of the visualization image of schooling fish as the target fish group visualized by horizontally and vertically. It has the longest duration of 90 ' and 250 PWM has a time duration of 10' shows the difference in the area of schooling fish in four zones. 195, 145 and 95 PWM with each time duration of 10' dominant schooling fish were in the main zone and influence zone, the lowest two light intensities of PWM values were 5 and 20, there are three zones namely center zone, main zone, and shadow zone, schooling fish were increasing with movement pattern by revolving the light source at shadow zone. The approached fish were forming schooling fish because they were attracted to light, with changes in the PWM value that can model the movement patterns of schooling fish.

Structures and infrastructures can modify aeolian sedimentary dynamics as has occurred in the arid transgressive dunefield of Maspalomas (Gran Canaria, Canary Islands), where an aeolian shadow zone has been formed leeward of a tourist resort (Playa del Ingles). The aim of this paper is to analyse spatial and statistically the influences of vegetation and topography on wind flow across this shadow zone. An experiment was carried out in March 2017, collecting wind speed and direction from 5 transects with anemometers at 0.40 m height. Simultaneously, a drone flight was carried out, from which an orthophoto and digital elevation and surface models (DEM and DSM) were obtained. Distance from the resort, and the presence of vegetation were found to influence transects dominated by erosional processes. Transects that do not display erosional processes were primarily affected by the presence of vegetation. The local wind field changes at a similar distance across the transects downwind from the resorts indicating an acceleration or reattachment of the wind at this distance downwind. The vegetation role in this aeolian shadow zone could be a key to the future evolution of the area resulting in either further stabilization, or alternatively, the continued deflation of the area.

This paper describes the world's first successful simulation for lateral cutoff phenomena of sonic boom far from the flight path due to variation in atmospheric temperature with altitude. A flow field around an axi-symmetric paraboloid has been analyzed by the full-field simulation method that solves the three-dimensional Euler equations with a gravity term to create a horizontally stratified atmosphere. A solution-adapted structured grid is constructed to align the grid lines with the front and rear shock-wave surfaces in the entire domain, including the near field around a supersonic body and far field reaching the ground beyond lateral cutoff. The flight is assumed to have a speed of Mach 1.2 at an altitude of 10 km, and the computational domain ranges over a distance of 30 km from the axis of symmetry. The computational results show that the evanescent wave in the shadow zone beyond lateral cutoff decays exponentially and changes into a progressive rounding waveform. The characteristics of the waveform transition are in good agreement with those observed in the flight tests. Therefore, the full-field simulation is recognized as a promising approach for investigating sonic boom strength in the full extent of sonic boom noise, including lateral cutoff and evanescent waves. Moreover, the computational results clarify that sonic boom focusing occurs above the ground, except for the vicinity of the ground, and the focusing strength along the lateral cutoff curve detected from the three-dimensional shock-wave surface increases with altitude. The results of ray tracing analysis collaborate the reasonability of the simulation results, and the caustic of downward convex agrees well with the lateral cutoff curve. In the shadow zone, the magnitude of exponential decay increases with altitude, and the lateral distance where the pressure rise decreases rapidly shortens with altitude.

Noise barriers are a critical part of noise mitigation in urban and rural areas. In this study, a comparison of the insertion loss calculations of noise barriers via the Finite Element Method (FEM) and various formulae (Kurze&ndash, Anderson, ISO 9613-2/Tatge, Menounou) is presented in the case of two-dimensional acoustic radiation problems. Some of the cases explored include: receiver in the illuminated zone, in the shadow zone, in the shadow border, source in medium, long, short distance from the barrier, source and receiver near barrier, and source above the barrier. Comparisons of the results indicate that FEM results comply well (less than 1 dB in each case) with Menounou&rsquo, s formula which in turn complies with the analytic solution (MacDonald Solution). In certain cases, the differences between FEM and Menounou&rsquo, s formula compared to Kurze&ndash, Anderson and ISO 9613-2/Tatge formulae are substantial (source and receiver near the barrier (10 dB) and source near the barrier and receiver in the shadow border (5 dB)). Similar differences are also confirmed by the analytic solution. The findings suggest that FEM can be applied effectively for the precise estimation of the insertion loss of noise barriers. Especially in cases where ISO 9613-2 formula shows large deviations from the analytic solution (e.g., near barrier), possible applications may arise in cases such as balconies, facades, etc. Furthermore, the study supports the idea that FEM could possibly be effectively utilized in real life applications for microscale urban acoustic modeling as a viable alternative to expensive noise prediction software.

Barriers are increasingly used to protect the pedestrian and neighboring buildings from construction noise activities. This study aims to investigate the suitability of applying active noise control on barriers in a construction site to protect the street area and neighboring buildings. Transducers that are simulated in this work are close to the barrier, and their optimal positions are defined in such a way that the control system has the maximum performance at the neighboring areas close to the construction sites. To begin with, the suitable location of the control sources is found when the total squared pressure is minimized at the positions of noise receivers. The suitable location of the error sensors is, then, found when the control sources are fixed at the position of the previous step and the total squared pressure is minimized at the error sensors. The best location for the error sensors is defined when the maximum reduction is achieved in the target area. It is observed that suitable positions for the transducers depend on the location of target areas for noise control, the position of the noise source, and its operating frequency. In this investigation, a unique configuration is proposed for the transducers that achieves a comparable reduction both at the street area and the neighboring buildings, simultaneously. The results show that the active noise barrier with a height of 2.5 m can achieve an extra insertion loss in the street zone, varies from 9.3 to 16.4 dB (in comparison with passive noise barrier) when the distance of the noise source from the barrier changes in the range of 7 to 1 m, respectively. Those values are of the same order for the passive noise attenuation. Furthermore, similar results are achieved when attempting to cancel the shadow zone of a fa&ccedil, ade 15 m away from the barrier.

This article aims to investigate if the proportion of the rotor area of a wind turbine that is in the refractive shadow zone according to a ray tracing algorithm coupled to meteorological forecast data is correlated to sound levels and amplitude modulation. The acoustic station is situated 950 m from a wind farm in Northern Sweden and the measurement period is seven months. On average, 1.9 dBA lower sound levels are measured when the part of the rotor disk of the closest turbine is in the refractive shadow zone. A higher probability of amplitude modulations are observed when around half of the turbine rotor is within the refractive shadow zone compared to conditions with no shadow zone present.

Observational analysis has revealed an apparent immobility of giant sand waves on the Taiwan Banks, while sand waves on the eastern Taiwan Banks show distinct dynamics influenced by the underlying larger-scale sand ridge bedforms. In this study, the effects of these sand ridge bedforms on sand wave migration and the local hydrodynamic environment were investigated using bathymetric and hydrodynamic datasets from 2016 and 2018. Upon separating the NNW-SSE sand ridge crest, the opposing sand wave migration and complementary sediment loss/gain on either side of the sand ridge are interpreted as convergence processes that serve to maintain the shape of the sand ridge. Analysis of the hydrodynamics revealed that, during the flood phase, the northward directed flow on the western side of the ridge crest was enhanced due to rapid shoaling. This caused the development of a flow shadow zone on the eastern side of the ridge crest, where the flow was rotated and weakened. During a tidal cycle, the dominance of the flood current on the western side of the ridge resulted in northward migration of sand waves. Conversely, due to the weakened flood current on the eastern side of the ridge, sand waves migrated southward in response to the stronger ebb current. This study thus provides insights into bedform dynamics in complex morphological settings and the maintenance mechanism of morphodynamic bedform systems.

Multi-purpose Artificial Reefs (MPARs) are structures that may provide aesthetically acceptable coastal protection and improve recreational outcomes. Twenty years after construction of the first MPAR, Narrowneck Reef on the Gold Coast of Australia, most of the available literature is still focused on the planning, design and construction of such structures and peer-reviewed publications on their post-construction monitoring, interaction with sediment transport and impacts on coastal morphology are lacking. The aim of this paper is to evaluate how does Narrowneck Reef influence the sediment transport, and morphological changes around the anthropogenic structure, two decades after construction. To do so, a combination of ten high spatial resolution topo-bathymetric surveys from the top of the dune to the 10 m depth captured over 21 months and a series of 60 simulations using a calibrated numerical model were used. Our results demonstrate that: although not expected during design or reported in similar structures, sand can bypass the MPAR around its offshore end; under oblique waves, the longshore currents are deflected as they pass the reef, resulting in a shadow zone on the downdrift side where sand deposits; the bar crest tends to be higher on the reef's updrift side compared to downdrift, indicating that the MPAR can act as a store for sediments, as initially designed. Furthermore, the MPAR can act to stabilise the bar as it moves onshore with a downdrift offset of the inner bar as a result of low oblique wave incidence. The results presented here demonstrate that the short-term response to the MPAR twenty years after construction is more closely related to the updrift build up of sand and the deflection of longshore currents as they encounter the reef than to the dissipation of wave energy. This is because MPARs are designed to dissipate just enough wave energy so that they can achieve their recreational goal (surfing).

To predict ice accretion on the helicopter rotor more accurately, a three-dimensional Eulerian method with a shadow zone dispersion model is developed for calculating the water collection efficiency on blades in the unsteady vortex flowfield of the rotor. Firstly, the unsteady vortex flowfield of the rotor is calculated using a CLORNS code. Secondly, considering the 3-D effect of the rotor deeply, the droplet flowfield on the same embedded grids is solved by the Eulerian method to overcome the defects of traditional 2-D calculation methods for predicting rotor icing. To increase the stability and efficiency of the Eulerian method, the shadow zone dispersion model is presented. Thirdly, the calculated results are respectively validated through the ice amount comparisons with experimental results of UH-1H rotor and SRB rotor. The simulated results show that the blade-tip vortex has a significant effect on the water collection efficiency and causes a drop in the water collection amount along the blade spanwise direction. Finally, the effects of the advance ratio and the forward tilting angle of the rotor shaft on the water collection efficiency are calculated and analyzed, and some new conclusions are obtained. In forward flight, the blade-tip vortex has a more obvious effect on the water collection efficiency in the advancing blade than that in the retreating blade, and this effect decreases with the increase of the advance ratio and the forward tilting angle.

Underwater noise from impact pile driving of 512 -m-long conductor casings was measured at a deep-water offshore oil platform in the Santa Barbara Channel. Beamforming measurements, obtained with a vertical array, confirmed that the primary wave front generated by hammering the conductor casing was a Mach cone propagating at an angle of 17.6° below the horizontal. Analysis of the processed array data also revealed the presence of high-frequency secondary waves at angles steeper than 45° below the horizontal. These secondary waves, which appeared to be generated near the sea-surface, dominated the acoustic spectrum of the pulses at frequencies above 1 kHz. Shallow hydrophone measurements outside the Mach cone showed clear evidence of a surface shadow zone, which was caused by the strong downward directivity of the source. Although reflected waves, diffraction, and secondary waves still produced sound inside the surface shadow zone, sound levels were 10-15 dB lower in this region. Long-term hydrophone measurements showed that there was little difference (±1 dB) in mean sound levels from impact hammering of different conductors installed at the same platform over three months.

A combination of magnetotelluric (MT) measurements on the surface and in boreholes (without metal casing) can be expected to enhance resolution and reduce the ambiguity in models of electrical resistivity derived from MT surface measurements alone. In order to quantify potential improvement in inversion models and to aid design of electromagnetic (EM) borehole sensors, we considered two synthetic 2D models containing ore bodies down to 3000 m depth (the first with two dipping conductors in resistive crystalline host rock and the second with three mineralisation zones in a sedimentary succession exhibiting only moderate resistivity contrasts). We computed 2D inversion models from the forward responses based on combinations of surface impedance measurements and borehole measurements such as (1) skin-effect transfer functions relating horizontal magnetic fields at depth to those on the surface, (2) vertical magnetic transfer functions relating vertical magnetic fields at depth to horizontal magnetic fields on the surface and (3) vertical electric transfer functions relating vertical electric fields at depth to horizontal magnetic fields on the surface. Whereas skin-effect transfer functions are sensitive to the resistivity of the background medium and 2D anomalies, the vertical magnetic and electric field transfer functions have the disadvantage that they are comparatively insensitive to the resistivity of the layered background medium. This insensitivity introduces convergence problems in the inversion of data from structures with strong 2D resistivity contrasts. Hence, we adjusted the inversion approach to a three-step procedure, where (1) an initial inversion model is computed from surface impedance measurements, (2) this inversion model from surface impedances is used as the initial model for a joint inversion of surface impedances and skin-effect transfer functions and (3) the joint inversion model derived from the surface impedances and skin-effect transfer functions is used as the initial model for the inversion of the surface impedances, skin-effect transfer functions and vertical magnetic and electric transfer functions. For both synthetic examples, the inversion models resulting from surface and borehole measurements have higher similarity to the true models than models computed exclusively from surface measurements. However, the most prominent improvements were obtained for the first example, in which a deep small-sized ore body is more easily distinguished from a shallow main ore body penetrated by a borehole and the extent of the shadow zone (a conductive artefact) underneath the main conductor is strongly reduced. Formal model error and resolution analysis demonstrated that predominantly the skin-effect transfer functions improve model resolution at depth below the sensors and at distance of $$\sim $$ 300–1000 m laterally off a borehole, whereas the vertical electric and magnetic transfer functions improve resolution along the borehole and in its immediate vicinity. Furthermore, we studied the signal levels at depth and provided specifications of borehole magnetic and electric field sensors to be developed in a future project. Our results suggest that three-component SQUID and fluxgate magnetometers should be developed to facilitate borehole MT measurements at signal frequencies above and below 1 Hz, respectively.

This study aims to determine if large-scale choked panel destress blasting can provide sufficient beneficial stress reduction in highly-stressed remnant ore pillar that is planned for production. The orebody is divided into 20 stopes over 2 levels, and 2 panels are choke-blasted in the hanging wall to shield the ore pillar by creating a stress shadow around it. A linear-elastic model of the mining system is constructed with finite difference code FLAC3D. The effect of destress blasting in the panels is simulated by applying a fragmentation factor (α) to the rock mass stiffness and a stress reduction factor (β) to the current state of stress in the region occupied by the destress panels. As an extreme case, the destress panel is also modeled as a void to obtain the maximum possible beneficial effects of destressing and stress shadow. Four stopes are mined in the stress shadow of the panels in 6 lifts and then backfilled. The effect of destress blasting on the remnant ore pillar is quantified based on stress change and brittle shear ratio (BSR) in the stress shadow zone compared to the base case without destress blasting. To establish realistic rock fragmentation and stress reduction factors, model results are compared to measured stress changes reported for case studies at Fraser and Brunswick mines. A 1.5 MPa immediate stress decrease was observed 20 m away from the panel at Fraser Mine, and a 4 MPa immediate stress decrease was observed 25 m away at Brunswick Mine. Comparable results are obtained from the current model with a rock fragmentation factor α of 0.2 and a stress reduction factor β of 0.8. It is shown that a destress blasting with these parameters reduces the major principal stress in the nearest stopes by 10–25 MPa. This yields an immediate reduction of BSR, which is deemed sufficient to reduce volume of ore at risk in the pillar.

Large parts of tropical coastlines are influenced by the presence of reefs that shape its coastline. Wave attenuation crossing reefs as they approach the coast results in accretionary coastal features developed in its shadow zones. With the aim of assessing the level of wave exposure of the coastline under different sea-level rise scenarios, numerical modeling experiments have been designed considering a coastline segment of approximately 450 km in northeast Brazil. Results show the distribution of wave power along the area of interest, with higher values being found in areas without reefs. However, when considering sea-level rise scenarios, it is behind the reefs where the maximum differences in wave power are observed. The increase in the free surface over the reef structures as a result of rising sea level reduces the wave attenuation effects caused by these structures. Thus, the waves hit the shore with greater force in the shadow zone protected by the reef. Here, we demonstrate that regions within the reef shadow zones are most strongly affected by sea-level rise with up to a 90% increase in the wave power, which will lead to increase in sediment transport and erosion processes. Such processes indicate a trend toward coastline flattening and alignment in response to less effective shadow zones.

We have developed a calibrated, simple time-lapse seismic method for estimating saturation changes from the CO2CO2-storage project at Sleipner offshore Norway. This seismic method works well to map changes when CO2CO2 is migrating laterally away from the injection point. However, it is challenging to detect changes occurring below CO2CO2 layers that have already been charged by some CO2CO2. Not only is this partly caused by the seismic shadow effects, but also by the fact that the velocity sensitivity for CO2CO2 change in saturation from 0.3 to 1.0 is significantly less than saturation changes from zero to 0.3. To circumvent the seismic shadow zone problem, we combine the time-lapse seismic method with time-lapse gravity measurements. This is done by a simple forward modeling of gravity changes based on the seismically derived saturation changes, letting these saturation changes be scaled by an arbitrary constant and then by minimizing the least-squares error to obtain the best fit between the scaled saturation changes and the measured time-lapse gravity data. In this way, we are able to exploit the complementary properties of time-lapse seismic and gravity data. © 2017 Society of Exploration Geophysicists and American Association of Petroleum Geologists. All rights reserved.

T waves are conventionally defined as seismically generated acoustic energy propagating horizontally over long distances within the minimum sound speed layer in the ocean (SOFAR axis minimum). However, T waves have also been observed by ocean-bottom seismometers in ocean basins at depths greater than the SOFAR axis minimum. Previously, non-geometrical processes, such as local scattering at rough seafloor and water-sediment interface coupling, have been proposed as possible mechanisms for deep seafloor detection of T waves. Here, we employ a new T-wave modeling approach based on hydroacoustic ray theory to demonstrate that seismoacoustic energy can propagate to reach deep seafloor, previously considered as shadow zone of acoustic propagation. Our new hydroacoustic simulations explain well the observations of T waves on ocean-bottom seismometers at deep ocean basins east of Taiwan, and shed new light on the mechanism for deep ocean T-wave propagation.

Movable-bed large-scale laboratory experiments were conducted to examine the fate and quantify the benefits of nearshore placed dredged material. Two tests were performed on a beach classified as eroding [19] for mounds placed in the active zone described by Hands and Allison [12] at two depths. Mound sand was dyed to provide contrast and to differentiate it from the native sand beach. Beach surveys were performed intermittently during each experiment with a laser scanner. In addition to beach change elevations, the scanner provided RGB color components, which permitted tracking of the mound sand. The experiments showed that the mound sand dispersed rapidly and was transported mainly downdrift. Sand accumulation was observed on the beach onshore and adjacent to the mounds mainly due to wave sheltering of the mounds described as the longshore effect by [28] . There was little contribution to onshore accretion from cross-shore migration of the mounds. Beach response was similar to that of an offshore breakwater in which the mounds provided a wave shadow zone to the leeward beach. The results from the experiment will provide validation data for the numerical morphological model C2SHORE [15] .

The presence of multiples has been investigated in Onshore Niger Delta using 3D seismic data. The aim of the study was to investigate the characteristics of reflection events beyond 3s two way time on seismic data behind the boundary faults associated with the shadow zone. This involves detailed velocity analysis on semblance plot panel and accounting for moveouts due to reflections away and within the shadow zone. Interval velocity-depth models were generated from the velocity analysis and analyzed for shadow effect in the data. Results of the study revealed the presence of two velocity scenarios Onshore Niger delta. These are the primary and lower than normal velocities away and within the shadow zone, respectively. The interval velocity-depth models and their overlays on the seismic show a constant increase of velocity with depth for the primary model which seems normal, but this is contrary to the lower than normal velocity model where low seismic velocities predominate beyond 3s two way time (3.8 km), especially at the footwall of the boundary fault. These variations are likely due to the fact that sediments at the footwall of the boundary fault are thicker, compacted and thus yield stronger reflectors than the corresponding sediments away from the faults. The lower than normal velocity reflections in the absence of overpressure and anisotropy, which are also causes of low velocity reflections, are attributed to interbed multiple reflections in the data. Key words: Seismic velocity, primary reflections, multiple reflections, boundary fault, multiple generators.

The lithosphere is the rigid outer shell of the Earth, composed of the crust and the rigid uppermost mantle. The lateral variation of lithosphere is believed to be closely related to the foci of intraplate earthquakes and volcanism, the location of large ore deposits and diamond-bearing kimberlites, and the formation of oil/gas-bearing sedimentary basins. Understanding the fine-scale structure of the lithosphere is therefore one of the most fundamental tasks in Earth sciences, and has important implications for society in terms of economic prosperity and hazard mitigation. Seismic tomography is the main technique available to image the subsurface structure of the Earth across a range of scales. Conventional seismic tomography exploits the seismic waves emitted by earthquakes. However, because most large earthquakes occur at plate boundaries and most continents, including Australia, are not seismically active, earthquake-based tomography suffers from uneven distributions of earthquakes and has difficulties in deciphering fine-scale structures of the Earth in seismically quiet continents. In the past decade, the advent of ambient noise tomography (ANT) has revolutionized seismic tomography because it can overcome the limitations of conventional earthquake surface wave tomography. This technique uses diffuse background seismic energy, mostly comes from the interaction of ocean waves with the crust. Empirical Green’s functions of surface waves passing between a pair of stations are extracted by cross-correlating continuous time series of ambient noise. Within a regional seismic array, all inter-station measurements of surface-wave dispersion can be measured and tomography can be performed to image the underling lithospheric structure. In this study, we demonstrate the applications of broadband ANT in mapping fine-scale lithosphere structures around the world using continuous seismic data.

Accurate prediction of wind turbine noise propagation over long distances requires modeling the dominant broadband aerodynamic noise sources, as well as the main outdoor sound propagation effects. In this study, two methods are compared to include extended aeroacoustic source models in a parabolic equation (PE) code for wind turbine noise propagation in an inhomogeneous atmosphere. In the first method, an initial starter is obtained for each segment of the blade using the backpropagation approach. In the second method, the blade segments are viewed as moving monopole sources, and only a limited number of PE simulations are needed for different source heights across the rotor plane. The two methods are compared to the point source approximation first in a homogeneous medium for validation purposes, and then in a stratified inhomogeneous atmosphere. The results show that an extended source model is necessary to calculate the sound pressure level upwind, where a shadow zone is present, and obtain the correct amplitude modulation levels. Furthermore, the second method is seen to yield as accurate results as the first method when a sufficient number of source heights is considered with a computation time that is much reduced.

We perform numerical calculations for onshore seismic amplifications, taking into consideration the effect of bathymetric features on the propagation of seismic movements. To this end, the boundary element method is applied. Boundary elements are employed to irradiate waves and, consequently, force densities can be obtained for each boundary element. From this assumption, Huygens' principle is applied, and since the diffracted waves are built at the boundary from which they are radiated, this idea is equivalent to Somigliana's representation theorem. The application of boundary conditions leads to a linear system being obtained (Fredholm integral equations). Several numerical models are analyzed, with the first one being used to verify the proposed formulation, and the others being used to estimate onshore seismic amplifications due to the presence of bathymetric features. The results obtained show that compressional waves (P-waves) generate onshore seismic amplifications that can vary from 1.2 to 5.2 times the amplitude of the incident wave. On the other hand, the shear waves (S-waves) can cause seismic amplifications of up to 4.0 times the incident wave. Furthermore, an important result is that in most cases the highest seismic amplifications from an offshore earthquake are located on the shoreline and not offshore, despite the seafloor configuration. Moreover, the influence of the incident angle of seismic waves on the seismic amplifications is highlighted.

Presently, there are a lot of observations on the significant impact of strong remote earthquakes on underground water and local seismicity. Teleseismic wave trains of strong earthquakes give rise to several hydraulic effects in boreholes, namely permanent water level changes and water level oscillations, which closely mimic the seismograms (hydro-seismograms). Clear identical anomalies in the deep borehole water levels have been observed on a large part of the territory of Georgia during passing of the S and Love–Rayleigh teleseismic waves (including also multiple surface Rayleigh waves) of the 2011 Tohoku M9 earthquake. The analysis carried out in order to find dynamically triggered events (non-volcanic tremors) of the Tohoku earthquake by the accepted methodology has not revealed a clear tremor signature in the test area: the Caucasus and North Turkey. The possible mechanisms of some seismic signals of unknown origin observed during passage of teleseismic waves of Tohoku earthquake are discussed.

Shock waves and impact of the Chelyabinsk Meteorite fragments on the ground initiated various waves in the atmosphere and the earth. Three different sources of seismic and infrasound waves were found by arrival time and azimuth of seismic and infrasound waves recorded by the International Monitoring System.

Indonesia’s strategic position between two continents and two oceans has resulted in an obligation for Indonesia to be involved in various international cooperation and international conflicts. The declaration of the development of the maritime sector to be the cornerstone of Indonesia’s main strength requires support from the air defense sector. The current condition of Indonesia’s air defense sector, especially the Air Surveillance Radar has not worked optimally resulting in an air defense operation that has not been maximized. The properties of high-frequency electromagnetic waves used in Doppler radar have a straight line of sight. Mountains, hills, and artificial objects/buildings can become obstacles, create blank areas (areas that cannot be covered by radar) behind them, and reduce the performance of the radar coverage. The use of sensing technology, in particular, the geographic information system to determine the position of air surveillance radar placing is an effective solution to optimize the coverage radars exist. The rectangular rule approach method combined with the land surveying technique is a combination of methods that can be used to measure the volume of air defense radar coverage. The level optimization of radar position planning point can be determined by processing the obstacle volume, land slope, earthquake and landslide vulnerability, and land cover conditions into the calculation of the fuzzy inference system technique. This study examines the concept of using Geographic Information Systems to measure the level of radar optimization when placed in a planned position. This research aims to produce a method review on optimizing the performance of air surveillance radar coverage by utilizing remote sensing technology to determine the radar placement position.

The great Sumatra-Andaman earthquake of 26 December 2004 caused seismic waves propagating through the solid Earth, tsunami waves propagating through the ocean and infrasound or acoustic-gravity waves propagating through the atmosphere. Since the infrasound wave travels faster than its associated tsunami, it is for warning purposes very intriguing to study the possibility of infrasound generation directly at the earthquake source. Garces et al. (2005) and Le Pichon et al. (2005) emphasized that infrasound was generated by mountainous islands near the epicenter and by tsunami propagation along the continental shelf to the Bay of Bengal. Mikumo et al. (2008) concluded from the analysis of travel times and amplitudes of first arriving acoustic-gravity waves with periods of about 400–700 s that these waves are caused by coseismic motion of the sea surface mainly to the west of the Nicobar islands in the open seas. We reanalyzed the acoustic-gravity waves and corrected the first arrival times of Mikumo et al. (2008) by up to 20 min. We found the source of the first arriving acoustic-gravity wave about 300 km to the north of the US Geological Survey earthquake epicenter. This confirms the result of Mikumo et al. (2008) that sea level changes at the earthquake source cause long period acoustic-gravity waves, which indicate that a tsunami was generated. Therefore, a denser local network of infrasound stations may be helpful for tsunami warnings, not only for very large earthquakes.

Ocean acoustic tomography depends on a suitable reference ocean environment with which to set the basic parameters of the inverse problem. Some inverse problems may require a reference ocean that includes the small-scale variations from internal waves, small mesoscale, or spice. Tomographic inversions that employ data of stable shadow zone arrivals, such as those that have been observed in the North Pacific and Canary Basin, are an example. Estimating temperature from the unique acoustic data that have been obtained in Fram Strait is another example. The addition of small-scale variability to augment a smooth reference ocean is essential to understanding the acoustic forward problem in these cases. Rather than a hindrance, the stochastic influences of the small scale can be exploited to obtain accurate inverse estimates. Inverse solutions are readily obtained, and they give computed arrival patterns that matched the observations. The approach is not ad hoc, but universal, and it has allowed inverse estimates for ocean temperature variations in Fram Strait to be readily computed on several acoustic paths for which tomographic data were obtained.

International audience; This study proposes to couple a source model based on Amiet's theory and a parabolic equation code in order to model wind turbine noise emission and propagation in an inhomogeneous atmosphere. Two broadband noise generation mechanisms are considered, namely trailing edge noise and turbulent inflow noise. The effects of wind shear and atmospheric turbulence are taken into account using the Monin-Obukhov similarity theory. The coupling approach, based on the backpropagation method to preserve the directivity of the aeroa-coustic sources, is validated by comparison with an analytical solution for the propagation over a finite impedance ground in a homogeneous atmosphere. The influence of refraction effects is then analyzed for different directions of propagation. The spectrum modification related to the ground effect and the presence of a shadow zone for upwind receivers are emphasized. The validity of the point source approximation that is often used in wind turbine noise propagation models is finally assessed. This approximation exaggerates the interference dips in the spectra, and is not able to correctly predict the amplitude modulation.

The adaptive optimized window generalized S transform (AOGST) variant with frequency and time is a method for the time–frequency mapping of a signal. According to the AOGST method, an optimized regulation factor is calculated based on the energy concentration of the S transform. The value of this factor is 1 for standard S transform where in the AOGST method its value is limited by the interval of [0, 1]. However, AOGST may not produce an acceptable resolution for all parts of the time–frequency representation. We applied aggregation of confined interval-adaptive optimized generalized S transforms (ACI-AOGST) instead of the AOGST method. The proposed method applies the modified AOGST method to specific frequency and time intervals. By calculating regulation factors for limited frequency and time intervals of signal, arranging them in a suitable order and applying the ACI-AOGST one can provide a transformation with lowest distortion and highest resolution in comparison to other transformations. The proposed method has been used to analyse the time–frequency distribution of a synthetic signal as well as a real 2D seismic section of a producing gas reservoir located south of Iran. The results confirmed the robustness of the ACI-AOGST method.

Large earthquakes that occur in subduction zones are likely to generate long-period ground motions that can cause severe damage even at great distances from the epicenter. We extracted surface-to-surface impulse response functions from the ambient seismic field recorded by offshore ocean bottom seismometers located atop the Nankai subduction zone and onshore stations. We showed that these offshore-onshore impulse response functions can be used to accurately simulate the long-period ground motions generated by an offshore moderate subduction earthquake. Moreover, we also found that the distributions of the earthquake and impulse response function pseudovelocity response spectra have similar maximum amplifications in the same area close to the earthquake epicenter. This suggests that the ambient seismic field recorded by the increasing number of ocean bottom seismometers around the world can be used to assess seismic hazard related to offshore subduction earthquakes without prior knowledge of the velocity structure.

The lowermost mantle of the Earth is characterized by seismic structures that range from a few tens to thousands of kilometers. At present, it is difficult to test hypotheses put forward to explain seismic observations due to poor seismic coverage, as particular earthquake-station geometries are needed. We demonstrate here that seismic noise correlations can be used to robustly image deep-mantle reflections with larger stacked amplitudes of reflected waves compared with earthquake data. In a comparison between noise and earthquake data, we find that the arrival times and the slowness of reflected waves, both sampling a region beneath Siberia, agree with those for a reflector at 2530 km depth, and the small amplitude reflections are sufficiently clear in the noise correlations to compare them reliably with synthetic data. Our data open exciting prospects for illuminating new target zones in the deep mantle to further constrain the dynamics and mineralogy of the deep Earth.

Considering that near-surface scattered waves could not be suppressed by conventional denoise method, this paper analyzes the characteristics of scattered waves and achieves the near-surface scattered wave separation by the seismic interferometry theory. Seismic data in mountain area is generally characterized by low signal to noise ratio, weak effective wave energy and strong near-surface scattered wave energy, so the near-surface seismic scattered waves must be firstly separated to improve the signal to noise ratio of seismic data during seismic data processing. The events of the near-surface seismic scattered wave in the adjacent common shot gathers are parallel. According to the near-surface scattered wave kinematics, the seismic interferometry method is used to eliminate the influence of seismic wave propagation in the same path, coherently enhance near-surface scattered waves, and then separate them from original seismic records. Taking the seismic data in mountain area in west China as an example, the energy of near-surface scattered wave is enhanced by direct wave field and full wave field seismic interferometry to separate the waves. As a result, the seismic data after processing generally eliminates near-surface scattered waves, verifying the validity and feasibility of the near-surface seismic scattered wave separation method. Key words: mountain seismic exploration, near-surface, seismic scattered wave, scattered wave separation, seismic interferometry

A tsunami is a natural coastal hazard generated in the deep ocean as a result of an earthquake, volcanic activity, submarine landslide or meteoritic impact. The 26th Dec. 2004 earthquake off the west coast of Sumatra, Indonesia generated one of the deadliest tsunami in history. It demolished the coastal areas of Indonesia, Sri Lanka, India, and Thailand, as these countries located shadow zone of this tectonic belt. Over thirty thousand loss their lives and also millions of worth extensive property damaged. As Sri Lanka situated in a shadow zone of the earthquake generated belt preparedness is very important factor. The study focused towards creation of a Tsunami risk map for Weligama area. The numerical simulation of tsunami inundation was carried out using ComMIT model with the major input parameters of earthquake source parameters, topography and bathymetry data. The December 2004 Sumatra Earthquake source parameters were used for generation, propagation, and coastal amplification of the tsunami waves and finally the inundation extent and water level was obtained to prepare large scale action maps on tsunami inundation to protect the coastal communities. The GIS tool has been used to incorporate the tsunami inundation depth to prepare the final tsunami risk map. Reliability of model results was compared with the field data and a high resolution QuickBird images with pre and post tsunami. The results from this study will be useful for long - term planning in vulnerable coastal communities and providing early warnings to take precautions to reduce impacts of tsunami in future.

The Sunda Strait is an important strait connecting Karimata and Java Seas with the Indian Ocean. The Sunda Strait is one of the busiest International Sea-lane in Indonesian Archipelago (ALKI). That is used for commercial shipping lanes and possibly for the military (submarines) cruise. For submarine operational purposes, a physical oceanographic dataset is needed which consisting of temperature, salinity, and sound speed. This article is analysing the seasonal variablity of thermocline and sound speed, including a shadow zone estimation. The 0.1 deg C gradient is applied for the thermocline layer determination during four seasons data in 2014. The dataset of INDESO Project (daily, 1/12 deg) has been used. In the North-West Season (January), thermocline layer (28 - 13.5 deg C) occurs at 77 - 155 m depth, has a range of 1,542 - 1,504 m/s sound speed. Those reveals shallower (40 - 130 m depth) of the thermocline layer (29 - 15.8 deg C) during the first Transitional Season (April), with the sound speed range 1,541 - 1,511 m/s. During South-East Season (July), the thermocline layer (29 - 15.4 deg C) has been deeper again (65 - 155 m depth), with 1,542 - 1,550 m/s of sound speed. While during the Second Transitional Season (October), the upper limit of thermocline layer (27 - 13.6 deg C) is a little bit shallower (55 - 155 m depth), with the sound speed range of 1,538 - 1,504 m/s. In annual average, the thermocline (29 - 13.6 deg C) in Sunda Strait laying in between an upper limit layer of 40 - 70 m depths and a bottom limit layer of 130 - 155 m depth. Those layers depth are estimated to be a probable shadow zone area with the sound speed range upper limit of 1,542 m/s. and the lower limit of 1,504 - 1,511 m/s.

International audience; Understanding the internal structure of an asteroid has important implications for interpreting its evolutionary history, for understanding its continuing geological evolution, and also for asteroid deflection and in-situ space resource utilisation. Given the strong evidence that asteroids are seismically active, an in-situ passive seismic experiment could provide information about the asteroid surface and interior properties. Here, we discuss the natural seismic activity that may be present on Didymoon, the secondary component of asteroid (65803) Didymos. Our analysis of the tidal stresses in Didymoon shows that tidal quakes are likely to occur if the secondary has an eccentric orbit. Failure occurs most easily at the asteroid poles and close to the surface for both homogeneous and layered internal structures. Simulations of seismic wave propagation in Didymoon show that the seismic moment of even small meteoroid impacts can generate clearly observable body and surface waves if the asteroid's internal structure is homogeneous. The presence of a regolith layer over a consolidated core can result in the seismic energy becoming trapped in the regolith due to the strong impedance contrast at the regolith-core boundary. The inclusion of macroporosity (voids) further complexifies the wavefield due to increased scattering. The most prominent seismic waves are always found to be those traveling along the surface of the asteroid and those focusing in the antipodal point of the seismic source. We find also that the waveforms and ground acceleration spectra allow discrimination between the different internal structure models.Although the science return of a passive seismic experiment would be enhanced by having multiple seismic stations, one single seismic station can already vastly improve our knowledge about the seismic environment and sub-surface structure of an asteroid. We describe several seismic measurement techniques that could be applied in order to study the asteroid internal structure with one three-component seismic station.

Currently, the wireless network environment of air node is constructed mainly of ground relay station. However, as the Korean Peninsula is composed of 70% mountainous region, there are multiple shadow zones. This is calling for effective measures to prevent aircraft from losing communication link during low-mid altitude missions. In this article we propose the utilization of Bezier Curve for estimation of aircraft flight path and control method for entering shadow zone. This method successfully estimated aircraft track, and analyzed the existence, disseminated the warning, and took measures to avoid the shadow zone before entering. This article, suggested after simulated experiments, proves that the method enables seamless communication during air

The formation and development of dunes depend on wind-blown sand movement which is affected by the characteristics of sand material, topography, wind regimes and other factors. In this paper, we investigated two sand shadow dune groups in Shigatse and Za’gya Zangbo of Tibet and an individual dune in Da Qaidam of Qinghai, and analyzed their topographies and morphologies, and the physical characteristics of the sand, wind regime and sand transport. Formed under harsh conditions behind hills, these mature sand shadow dunes are hundreds of meters long, have significant ridges and crescent dunes downwind, and have a hill pass on one or both sides. Wind tunnel experiments revealed that the hill gap and wind velocity are important factors in the formation of these dunes. Sand shadow dunes formed only when the gap spacing is two-thirds of the hill height. When wind velocities are 20 m/s, the sand body is divided into two parts. The hill pass allows the transport of sand by wind, creating a “narrow-pipe effect”, which causes the transported material to gradually accumulate in the center of the shadow zone. We observed that the following are needed for sand shadow dunes to form: (1) strong winds, sufficient sand, suitable obstacles and a dry climate; (2) one or both sides of the obstacle forming the shadow zone must have a hill pass; and (3) the windward side of the obstacle must have a wide, flat area, providing adequate spacing for wind flow and transport of material and the leeward side must have a sufficiently broad, flat area to allow the release of the transported material. Research results on these newly discovered dunes on the Qinghai-Tibet Plateau could contribute to the understanding of dune geomorphology.

We detected electromagnetic (EM) waves directly excited by earthquakes in a deep borehole and confirmed them by simultaneous capturing of their waveforms and of seismic waves measured at the same observation site. Furthermore, the excitation mechanism of the EM pulse was confirmed as the piezoelectric effect by a laboratory experiment, in which a seismic P-wave was readily generated by a small stress impact, and the EM wave was simultaneously excited basically by the P-wave. Here, we show behaviors of seismic waves and of their excited EM waves when small and large earthquakes occurred. We also found that EM waves excited by seismic waves have leaked out of the ground surface.

Background The curved shoreline shape of embayed beaches is one of its most notable characteristics and can be described using the parabolic bay shape equation (PBSE). Wave diffraction in and around the shadow zone is often regarded as the primary forcing mechanism leading to the prominent curvature of the shoreline. However, wave climate variables (wave direction, directional spreading and wave height) are shown to be influential in redistributing wave energy throughout the bay and in the shadow zone. Methods In this study, a process-based morphological model (Delft3D) is used for hydrodynamic and morphodynamic simulations of a schematic embayed beach. Wave forcing conditions are systematically varied between a mixture of time-invariant and time-varying cases. Results The role of diffraction is shown to be dominant only when the wave conditions are both narrow-banded ( 30°). Otherwise, as little as 6% variation in wave direction within a 90° range can account for the shoreline curvature in and around the shadow zone. Conclusion The degree to which wave direction and directional spreading vary through time therefore has a large effect on the equilibrium orientation and shoreline planform of the bay.