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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.

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.

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.

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.

A direct numerical simulation of the three-dimensional unsteady compressible Navier–Stokes equations is performed to investigate the infrasonic field generated in a realistic atmosphere by an explosive source placed at ground level. To this end, a high-order finite-difference method originally developed for aeroacoustic applications is employed. The maximum overpressure and the main frequency of the signal recorded at 4 km distance from the source location are about 4000 Pa and 0.2 Hz, respectively. The atmosphere is parametrized as a vertically stratified medium, constructed by specifying vertical profiles of the temperature and the horizontal wind which reproduce measurements. The computation is carried out up to 140 km altitude and 450 km range. The goal of the present paper is twofold. On the one hand, the feasibility of using a direct numerical simulation of the three-dimensional fluid dynamic equations for the detailed description of long-range propagation in the atmosphere is proven. On the other hand, a physical analysis of the infrasonic field is realized. In particular, great attention is directed towards some important phenomena which are not taken into account or not well predicted by classical propagation models. To begin with, the present study clearly demonstrates that the weakly nonlinear ray theory may lead to an incorrect evaluation of the waveform distortion of high-amplitude waves propagating towards the lower thermosphere. In addition, signals recorded in the shadow zones are investigated. In this regard, the influence on the acoustic field of temperature and wind inhomogeneities of length scale comparable with the acoustic wavelength is analysed. The role of diffraction at the thermospheric caustic is finally examined and it is pointed out that the amplitude of the source may have a strong impact on the length of the shadow zone.

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.

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.

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

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.

Direct numerical simulations of the two-dimensional unsteady compressible Navier-Stokes equations are performed to study the acoustic field generated by an infrasonic source in a realistic atmosphere. Some of the main phenomena affecting the propagation of infrasonic waves at large distances from the source are investigated. The effects of thermal and wind-related refraction on the signals recorded at ground level are highlighted, with particular emphasis on the phase shift induced by the presence of caustics in the acoustic field. Nonlinear waveform steepening associated with harmonic generation, and period lengthening, both of which are typical of large source amplitudes, are illustrated, and the importance of thermoviscous absorption in the upper atmosphere is clearly demonstrated. The role of diffraction in the shadow zone, around caustics and at stratospheric altitudes is also pointed out. The Navier-Stokes equations are solved using high-order finite-differences and a Runge-Kutta time integration method both originally developed for aeroacoustic applications, along with an adaptive shock-capturing algorithm which allows high-intensity acoustic fields to be examined. An improvement to the shock detection procedure is also proposed in order to meet the specificities of nonlinear propagation at long range. The modeling as well as the numerical results are reported in detail and discussed.

The goal of the present paper is to numerically investigate the effects produced by a vertical barrier located inside the ground, when the soil is subjected to seismic waves coming from a seismic source with a planar wave front. Firstly, the acceleration field on the ground surface is computed by varying both geometrical and mechanical properties of the barrier in order to determine, through a parametric study, the optimal barrier configuration to minimize the maximum magnitude of surface acceleration inside the shielded zone. Then, the above configuration is employed in the framework of a seismic analysis: a portion of a colonnade in Pompeii (Naples, Italy) is examined, with such a colonnade assumed to be located inside the shielded zone. A comparison of the seismic behaviour of such a heritage building is provided for the two cases of ground with or without the above vertical barrier.

20th International Symposium on Nonlinear Acoustics (ISNA) including the 2nd International Sonic Boom Forum (ISBF), Ecole Centrale Lyon, Lyon, FRANCE, JUN 29-JUL 03, 2015; International audience; Sonic boom is one of the key issues to be considered in the development of future supersonic or hypersonic civil aircraft concepts. The classical sonic boom, typical for Concorde with an N-wave shape and a ground amplitude of the order of 100 Pa, prevents overland flight. Future concepts target carefully shaped sonic booms with low amplitude weak shocks. However, sonic boom when perceived at the ground level is influenced not only by the aircraft characteristics, but also by atmospheric propagation. In particular, the effect of atmospheric turbulence on sonic boom propagation near the ground is not well characterized. Flight tests performed as early as the 1960s demonstrated that classical sonic booms are sensitive to atmospheric turbulence. However, this sensitivity remains only partially understood. This is related to the fact that i) turbulence is a random process that requires a statistical approach, ii) standard methods used to predict sonic booms, mainly geometrical acoustics based on ray tracing, are inadequate within the turbulent planetary boundary layer. Moreover, the ray theory fails to predict the acoustical field in many areas of interest, such as caustics or shadow zones. These zones are of major interest for sonic boom acceptability (highest levels, lateral extent of zone of impact). These limitations outline the need for a numerical approach that is sufficiently efficient to perform a large number of realizations for a statistical approach, but that goes beyond the limitations of ray theory. With this in view, a 3D one-way numerical method solving a nonlinear scalar wave equation established for heterogeneous, moving and absorbing atmosphere, is used to assess the effects of a 3D kinematic turbulence on sonic boom in various configurations. First, a plane N-wave is propagated in the free field through random realizations of kinematic fluctuations. Then the case of a more realistic Atmospheric Boundary Layer (ABL) is investigated, with a mean stratified wind superimposed to a 3D random turbulent realization. Propagation is performed either in the case of a shadow zone or of an atmospheric waveguide. To model the turbulent ABL, the mean flow and the fluctuations are handled separately. The wind fluctuations are generated using the Random Fluctuations Generation method assuming a von Karman spectrum and a homogeneous and isotropic turbulence. The mean stratified wind is modeled based on the Monin-Obhukov Similarity Theory (MOST). To illustrate the method, the typical case of a sunny day with a strong wind has been chosen. Statistics are obtained on several parameters. It shows the importance of turbulence, which leads to an increase of the mean maximum peak pressure in the shadow zone and to its decrease in the waveguide. Moreover, the formation of random caustics that can lead to an increase of the noise perceived locally is outlined.

51 short-period vertical North American and Canadian records of the Samoa earthquake 14 April 1957 were examined. Amplitudes of P were very large at the western stations (Δ < 84˚) and small at the stations to the east, 8 of which recorded P at distances greater than 100˚. There was a lack of stations at intermediate distances. At the greatest distance, 108˚.2, the P waves were not diffracted waves, for the phase had the same general character as at shorter distances; the period was 2 sec. From 70˚ to about 90˚ the Samoa P timedistance curve is steeper than the Jeffreys-Bullen curve. It had been found previously that from about 90˚ epicentral distance onwards the variation ot the P amplitude with distance was not always the same and also that the shadow zone seemed to begin at different distances. It is suggested that this be due to small regional differences of velocity in the deepest layer D" of the mantle.

This paper describes a methodology for minimising the length of a breakwater based on the desired level of operability for a berthed vessel in its shadow zone. The methodology uses random wave theory to propagate waves to the berth accounting for refraction, shoaling, transmission and diffraction to find whether the vessel response exceeds its threshold for a time series of wave data. A Monte Carlo simulation is used to create a time series which is used where limited wave data is available. The output of the research is the optimised topographical layout of the breakwater.

Akihiro Takeuchi1, Kan Okubo2 and Nobunao Takeuchi3 1Earthquake Prediction Research Center, Institute of Oceanic Research and Development, Tokai University 3-20-1 Orido, Shimizu-ku, Shizuoka 424-8610, 2Division of Information and Communications Systems Engineering, Tokyo Metropolitan University 6-6 Asahigaoka, Hino 191-0065, 3Research Center for Predictions of Earthquakes and Volcanic Eruptions, Graduate School of Sciences, Tohoku University 6-6 Aza-aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan

Time-dependent mild-slope equations have been extensively used to compute wave transformations near coastal and offshore structures for more than 20 years. Recently the wave absorption characteristics of a Wave Energy Converter (abbreviated as WEC) of the overtopping type have been implemented in a time-dependent mild-slope equation model by using numerical sponge layers. In this paper the developed WEC implementation is applied to a single Wave Dragon WEC and multiple Wave Dragon WECs. The Wave Dragon WEC is a floating offshore converter of the overtopping type. Two wave reflectors focus the incident wave power towards a ramp. The focussed waves run up the ramp and overtop in a water reservoir above mean sea level. The obtained potential energy is converted into electricity when the stored water drains back to the sea through hydro turbines. The wave reflectors and the main body (ramp and reservoir) are simulated as porous structures, exhibiting the same reflection, respectively absorption characteristics as obtained for the prototype Wave Dragon WEC. The wake effects behind a single Wave Dragon WEC are studied in detail for uni- and multidirectional waves. The shadow zone indicating the wake effect is decreasing with increasing directional spreading. The wake in the lee of a farm of five Wave Dragon WECs, installed in a staggered grid (3 WECs in the first row and 2 WECs in the second row), is calculated for three in-between distances of respectively D, 2D and 3D, with D the distance between the tips of the wave reflectors of a single WEC. As a result, a farm of five Wave Dragon WECs installed in a staggered grid with an in-between distance of 2D is preferred, when taking cost and spatial considerations into account. Time-dependent mild-slope equations have been extensively used to compute wave transformations near coastal and offshore structures for more than 20 years. Recently the wave absorption characteristics of a Wave Energy Converter (abbreviated as WEC) of the overtopping type have been implemented in a time-dependent mild-slope equation model by using numerical sponge layers. In this paper the developed WEC implementation is applied to a single Wave Dragon WEC and multiple Wave Dragon WECs. The Wave Dragon WEC is a floating offshore converter of the overtopping type. Two wave reflectors focus the incident wave power towards a ramp. The focussed waves run up the ramp and overtop in a water reservoir above mean sea level. The obtained potential energy is converted into electricity when the stored water drains back to the sea through hydro turbines. The wave reflectors and the main body (ramp and reservoir) are simulated as porous structures, exhibiting the same reflection, respectively absorption characteristics as obtained for the prototype Wave Dragon WEC. The wake effects behind a single Wave Dragon WEC are studied in detail for uni- and multidirectional waves. The shadow zone indicating the wake effect is decreasing with increasing directional spreading. The wake in the lee of a farm of five Wave Dragon WECs, installed in a staggered grid (3 WECs in the first row and 2 WECs in the second row), is calculated for three in-between distances of respectively D, 2D and 3D, with D the distance between the tips of the wave reflectors of a single WEC. As a result, a farm of five Wave Dragon WECs installed in a staggered grid with an in-between distance of 2D is preferred, when taking cost and spatial considerations into account.

In outdoor sound propagation, an inherent problem of the ray tracing method is its inability to determine the sound pressure level in the shadow zone, where geometrical rays do not penetrate. This is a serious problem in a turbulent atmosphere where significant sound energy will be scattered into the shadow. Empirical corrections that are determined from measurements or numerical simulations are limited to situations within the bounds of the empirical corrections. This paper describes a different approach where the ray tracing model is modified analytically into a scattered ray model. Rays are first diffracted from the shadow boundary, which is determined by the geometrical ray paths. The diffracted rays are then scattered by turbulence in their way to the receiver. The amount of scatter is determined from turbulence statistics that are determined from a Gaussian turbulence model. Most of the statistics are determined analytically except one element, which is determined empirically from numerical simulations. This turbulence scattered ray model is shown to have good accuracy against calculations based on the parabolic equation, and against previously published measurement data. It was found that the agreement is good both with and without turbulence, at distance up to 2 km from the shadow boundary.\ud \ud © 2009 Acoustical Society of America

An easy-to-apply computational procedure for the study of the acoustic performance of pairs of diffusively reflecting roadside barriers is described in detail, and an experimental verification of its predictions, carried out on a 1:10 scale model, is presented and discussed. It is shown that, in comparison with pairs of more traditional specularly reflecting noise barriers, significant attenuation benefits are obtained not only in the shadow zone behind the barriers, but also in the unprotected zone immediately above the barriers, which proves that diffusive traffic faces of the barriers may effectively help in counteracting multiple reflection effects.

In addition to reducing the incoming wave energy, submerged breakwaters also cause a setup of the sea level in the protected area, which is relevant to the whole shadow zone circulation, including alongshore currents and seaward flows through the gaps. This study examines such a leading hydraulic parameter under the simplified hypothesis of 2D motion and presents a prediction model that has been validated by a wide ensemble of experimental data. Starting from an approach originally proposed by Dalrymple and Dean [(1971). Piling-up behind low and submerged permeable breakwaters. Discussion note on Diskin et al. (1970). Journal of Waterways and Harbors Division WW2, 423–427], the model splits the rise of the mean water level into two contributions: one is due to the momentum flux release forced by wave breaking on the structure, and the other is associated with the mass transport process. For the first time, the case of random wave trains has been explicitly considered.

The seismic structure of Earth’s inner core is highly complex, displaying strong anisotropy and further regional variations. However, few seismic waves are sensitive to the inner core and fundamental questions regarding the origin of the observed seismic features remain unanswered. Thus, new techniques to observe different types of inner core waves are imperative to improve data coverage. Here, we detail our method for detecting exotic inner core phases such as PKJKP and PKIIKP, using inner core compressional waves as proof of concept. We use phase weighted stacking on long period data from a global distribution of stations, and employ several synthetic methods, including normal mode summation and SPECFEM, to identify and confirm the inner core phases. We present evidence for two observations of exotic inner core compressional waves, and apply the technique to a previously detected inner core shear wave. A possible new inner core shear wave remains unconfirmed. Additionally, we show how our method is important for rejecting potential observations, and distinguishing between waves with similar traveltime and slowness. The method is most successful for detecting exotic inner core compressional waves, and will provide a new approach for studying the compressional wave structures in the upper inner core.

We discuss the effect of motion on the scattering by an edge. To this end, one considers the simplest canonical structure formed by a uniformly moving perfectly conducting half-plane illuminated by a time-harmonic plane wave and investigates the effect of the motion on the reflection and shadow zones, aberration, Doppler shift, edge-diffracted wave, etc. The cases where the velocity is parallel and normal to the half-plane are considered separately. Some of the interesting results which were obtained, in addition to the classical Doppler shift and aberration phenomena, are that (i) the edge-excited wave is never time- harmonic while the waves excited by the plane (both in the shadow and in the reflection zones) are always time-harmonic, (ii) the shadow and reflection boundaries are not parallel to the incident and reflected rays, (iii) at certain values of the velocity and incidence angle, a shadow region appears in the apparent illuminated region while a lit region appears in the apparent shadow region, (iv) the moving half-plane provides, sometimes, energy to the reflected wave. The cases of v « c and v ~ c are examined in detail. © 2006 IEEE. Türkiye Bilimler Akademisi Manuscript received April 28, 2006; revised July 14, 2006. This work was supported by the Turkish Academy of Sciences (TUBA). M. Idemen is with the Yeditepe University, Faculty of Arts and Science, Department of Mathematics, Kayisdagi Caddesi, 81120 Kayisdagi/Erenköy, Istanbul, Turkey (e-mail: midemen@gmail.com). A. Alkumru is with the Gebze Institute of Technology, Department of Electronics Engineering, 41400 Gebze, Kocaeli, Turkey (e-mail: alkumru@gyte. edu.tr). Digital Object Identifier 10.1109/TAP.2006.884305

International audience; We report the observation of weak localization of seismic waves in a natural environment. It emerges as a doubling of the seismic energy around the source within a spot of the width of a wavelength, which is several tens of meters in our case. The characteristic time for its onset is the scattering mean-free time that quantifies the internal heterogeneity.

Electric and magnetic data were obtained above the focal area in association with the 1999 Izmit, Turkey earthquake. The acquired data are extremely important for studies of electromagnetic phenomena associated with earthquakes, which have attracted much attention even without clear physical understanding of their characteristics. We have already reported that large electric and magnetic variations observed during the earthquake were simply due to seismic waves through the mechanism of seismic dynamo effect, because they appeared neither before nor simultaneously with the origin time of the earthquake but a few seconds later, with the arrival of seismic wave. In this letter we show the result of our further analyses. Our detailed examination of the electric and magnetic data disclosed small signals appearing less than one second before the large signals associated with the seismic waves. It is not yet solved whether this observational fact is simply one aspect of the seismic dynamo effect or requires a new mechanism.

International audience; In many active margins, severe deformation is observed at the front of the overriding plate where seamounts or aseismicridges subduct. Such deformation appears to be a main tectonic feature of these areas which influences the morphologyand the seismicity of the margin. To better understand the different stages of seamount subduction, we have performedsandbox experiments to study in detail the evolution of deformation both in space and time and thus complement seismicimages and bathymetry interpretation. We focus, in this paper, on the surface deformation directly comparable with seafloormorphology. Two types of subducting seamounts were modelled: relatively small conical seamounts, and larger flat-toppedseamounts. The indentation of the margin by the seamount inhibits frontal accretion and produces a re-entrant. The marginuplift includes displacement along backthrusts which propagate from the base of the seamount, and out-of-sequenceforethrusts which define a shadow zone located on the landward flank of the seamount. When the seamount is totally buriedbeneath the margin, this landward shielded zone disappears and a larger one is created in the wake of the asperity due tothe elevated position of the de´collement. As a consequence, a section of the margin front follows behind the seamountto greater depth. A ‘slip-line’ network develops concurrently above the subducting seamount flanks from the transtensionalong the boundaries of the shadow zone. In a final stage, normal faults, controlled by the shape of the seamount, develop inthe subsiding wake of the asperity. Swath-bathymetric data from the Costa Rica margin reveal detailed surface deformationof the margin above three subducting seamounts. Shaded perspective views highlight the detailed structure of the seafloorand compare well with surface deformation in the sandbox experiments. The good correlation between the marine dataand experimental results strengthen a structural interpretation of the Costa Rican seamount subduction.

International audience; Seismo-Electromagnetic (SEM) waves observed by low-altitude satellites passing over seismic regions were studied. The data of the COSMOS-1809 satellite were analysed over the earthquake region in Armenia during the period from January 20 to February 17, 1989. Intense EM radiation at frequencies below 450 Hz was observed at the L-shells of the earthquake, during 12 orbits out of the 13 that passed within 6 ø in longitude from the epicenter, and during 1 out of 6 in the range of 6o-8 ø longitude away from this region. The other orbits, which passed 10ø-12 ø from the epicentre, showed no effect. To complete this study, we used the emissions observed by another low-altitude satellite (AUREOL-3). It is shown that during the event the seismic region is permanently radiating; the intensity and the envelope shape of the wave depend on its time relatively to the time of the earthquake. Their frequency spectra are compared to the average spectrum recorded in the same geomagnetic regions. Similar wave intensities and spectral distributions were observed on the two satellites during the seismic periods.

Since ray paths of direct P and S waves are largely distorted in a magma body, a seismic shadow zone is created. However, scattered or diffracted waves with very small amplitudes can arrive in the shadow zone because their ray paths are different from those of the direct waves. They become the first arrival in the shadow zone. More than 100 seismologists from many institutions in Japan joined together to perform an intensified seismic study in the Nikko-Ashio area, northern Kanto, Japan. It was suggested that there is a magma body beneath Mount Nikko-Shirane, an active volcano, that causes a seismic shadow zone, because P waves recorded by the joint observation are anomalously attenuated in cases when they propagate through a zone beneath the eastern part of the volcano. We developed a new method to estimate the shape of the anomalous attenuation zone by proposing the use of a new parameter, the energy ratio between directP or S waves and their coda waves, to discriminate whether or not each observation station is located inside or outside the shadow zone. We estimated the shape of the anomalous attenuation zone by dividing the study area into blocks with dimensions of 2 km × 2 km × 1 km and using the energy ratio data of P waves for local events. The obtained result shows the existence of an anomalous attenuation zone in the area east of Nikko-Shirane volcano with a diameter of about 10 km at depths greater than 3 km. It was also found from plots of deep event seismograms recorded by the same observation that travel times are delayed by about 0.7 s for ray paths crossing the anomalous attenuation zone obtained by the energy ratio data. This value requires the P wave velocity in the anomalous zone to be less than that of the surrounding crustal material by at least about 30%, suggesting the existence of a huge magma reservoir in this area.

Local earthquakes observed at Sendai, Japan, were analyzed to confirm the validity of a method of polarization analysis using the spectral matrix of seismic wave and its application to seismic reflection studies of the crust using local earthquake data. Reflectors (Bright spots) are known below the Nagamachi-Rifu fault, which caused an M 5.0 class event in 1998. Polarization analysis was applied to earthquake data in and around the fault. Use of the Z-parameter, which is defined using the eigenvalues of the spectral matrix and a statistical value representing the confidence level for the detection of the arrival of polarized waves, allowed detection of linearly and elliptically polarized waves in coda waves. The Z-parameter was also used to image the reflectors by using a migration technique that assumes the P×P and S×S reflection waves travel through a multi-layered velocity structure. Distinct reflectors were detected at depths of around 10 km, 14 km, 17 km, 21–26 km, 35 km and 40 km, that is, from deeper than the fault and the Moho. This study demonstrated the feasibility of using the spectral matrix of three-component seismic signal to detect polarized waves and to image reflectors in the earth’s crust and upper mantle.

A single force mechanism is investigated as the source of long-period seismic radiation from the 1975 Kalapana, Hawaii, earthquake (M_S = 7.1). The observed Love wave radiation pattern determined from the spectra of World-Wide Standard Seismograph Network and High Gain Long Period records at 100 s is two-lobed with azimuth, consistent with a near-horizontal single force acting opposite (strike ∼330°) to the observed displacement direction of the earthquake; this pattern is inconsistent with the expected double-couple pattern. Assuming a form of the force time history of a one-cycle sinusoid, the total duration of the event estimated from Rayleigh waves at two International Deployment of Accelerometers stations is approximately 180 s. The peak amplitude f_o of the time function is 1 × 10^(15) N from amplitudes of Love and Rayleigh waves. The interpretation is that the bulk of the seismic radiation was produced by large-scale slumping of a large area of the south flank of Kilauea volcano. The single force is a crude representation of the effect on the earth of the motion of a partially decoupled large slide mass. Using the mass estimated from the tsunami generation area (∼ 10^(15)–10^(16) kg), the peak acceleration of the slide block (0.1–1 m s^(−2)) inferred from the seismic force is comparable with the acceleration due to gravity on a gently inclined plane. The slump model for the Kalapana earthquake is also more qualitatively consistent with the large horizontal deformation (8 m on land) and tsunami associated with the earthquake, which are difficult to explain with the conventional double-couple source model. The single-force source has been used previously to model the long-period seismic waves from the landslide accompanying the eruption of Mount St. Helens volcano, and may explain other anomalous seismic events as being due to massive slumping of sediments or unconsolidated material and not to elastic dislocation.

Surface waves are now being used by several groups to map lateral heterogeneity [Nakanishi and Anderson, 1982, 1983, 1984a, b; Woodhouse and Dziewonski, 1984] and anisotropy [Tanimoto and Anderson, 1984a, b; Nataf et al. 1984] of the upper mantle on a global basis. The method involves measuring the phase and/or group velocity over hundreds of small arcs and long arcs connecting earthquakes and seismic stations. These averages are then converted to three-dimensional images of the seismic velocity structure, and, hence, this is a form of tomography. The large amount of data processing required is made feasible by the existance of long-period digital seismic networks including IDA (International Deployment of Accelerometers), SRO (Seismic Research Observatories), and GDSN (Global Digital Seismic Network). These instruments are operated by a variety of university and government groups including University of California, San Diego, U.S. Geological Survey, D.A.R.P.A., and U.S. Department of Energy with the cooperation of many countries. The global coverage is still very sparse compared to the analog W.W.S.S.N. (World Wide Standardized Seismic Network), but preliminary results are very encouraging. The possibility of an expanded global digital network of broadband seismic stations is now being pursued actively by the United States and several other countries. Because of the sparseness of the present network, mantle structure can only be mapped with fairly low resolving power. Only features with half wavelength of the order of 2,000 km can be detected.

Summary The magnitude of deep-focus earthquakes is so defined as to make the energy released in two shocks of the same magnitude equal, regardless of focal depth.—Charts are given which, in connection with the equations for the magnitude of shallow shocks, permit the calculation of the magnitude of a shock at any given depth if the maximum ground amplitude and the corresponding wave period of P, PP, or S at a given epicentral distance are known.—It is found that the energies released in the longitudinal and transverse waves of an earthquake are about equal, regardless of focal depth.—The “shadow zone” for P and S waves at epicentral distances near 10°, indicating a slight minimum in wave velocity at a depth near 100 km., has been confirmed, and quantitative results for amplitudes of P as a function of focal depth are given.—Earthquake magnitudes of 7 ¾ to 8 have been found throughout the range of focal depths, but, during the past forty years, seem to have been relatively less frequent in deep-focus than in shallow shocks. In contrast with shallow shocks, no deep-focus earthquakes of magnitudes 8 ¼ to 8 ½ have been established thus far. This indicates (but does not yet prove) that at depths of about 100 to 700 km. roughly one-tenth as much energy can be stored as at depths of 15 to 40 km. At a depth of about 700 km. earthquake activity seems to stop abruptly.—The amplitudes of surface waves in deep-focus shocks decrease with increasing focal depth approximately as given by the theory.