Types Of Seismic Waves Research Articles

Tom La Touche and the Great Assam Earthquake of 12 June 1897: Letters from the Epicenter

Richard Dixon Oldham's classic memoir on the great Mw = 8.1 Assam earthquake of 1897 is seminal for its seismological observations, insights, and conclusions (Oldham 1899). Teleseismic arrivals of waves from Shillong led Oldham (1858–1936) to distinguish the three types of seismic waves and eventually to recognize from them the distinctive presence of the Earth's core. Oldham, however, did not feel the earthquake. He had left the Calcutta office of the Geological Survey of India (GSI) in the care of his colleague Thomas Henry Digges La Touche (1856–1938) two weeks previously (see figure 1). Now recently discovered letters written by La Touche from Calcutta and the epicentral region to his wife, Nancy, provide a firsthand, day-by-day account of the post-earthquake investigation and include a seismogram from an instrument that he constructed in the field at a cost of “less than sixpence” from pieces of tin, a suspended boulder, a glass bead, and a bamboo needle that scratched a glass plate (LaTouche papers, 1880–1913). In his memoir Oldham notes that he focused his team of geologists on the physics of the earthquake. Their reports were submitted “under specific instructions to report only on the facts observed, and to refrain from any expressions of opinion as to the conclusions to be drawn, as this could only be profitably done after a review of the whole of the facts, of which only part could become known to each individually.” (Oldham 1899, p.257). He deduced from their observations that local accelerations in the earthquake had exceeded 1 g, that velocities had exceeded 3 m/s, that electrical currents in the ground had accompanied aftershocks, that postseismic crustal deformation continued to deform the plateau in the year following the earthquake, and that many of the largest aftershocks lay 15 km beneath the plateau. …

2301 鉄道車両の地震時挙動に関する研究(OS4-1 接触問題とトライボロジ(その1),OS4 接触問題とトライボロジ,オーガナイズド・セッション)

The seismic behavior of railway vehicle was investigated to consider the mechanism of derailment by an earthquake. A scale of 1 to 10 railway vehicle model was vibrated by two types of seismic wave, which are Niigata Prefecture Chuetsu Earthquake and Iwate Miyagi Inland Earthquake. The speed of the vibrated model were 0km/h, 3km/h, 6km/h and 9km/h. For each condition, the model was vibrated ten times and derailment probabilities were found. By this study, it was shown that derailment probabilities tend to be higher when railway vehicle is running. Also, it was found that limits of effective value of input and response acceleration are different for stopping vehicle and running vehicle.

Scientists examine seismic data from North Korean nuclear test

North Korea's unconfirmed nuclear test on 9 October displayed several characteristics not typical of earthquakes that indicate it was indeed a nuclear test, according to Paul Richards, a seismologist with the Lamont‐Doherty Earth Observatory of Columbia University, Palisades, N.Y.Richards said these characteristics include a type of seismic surface wave indicating the event occurred at shallow depth (less than one or two kilometers) and thus likely of anthropogenic origin; impulsive quality of the waves at the beginning of the seismogram; and very weak shear waves.

Seasonality in particle motion of microseisms

SUMMARY Microseisms are a continuous source of seismic signal which mainly consist of Rayleigh waves but are known to contain some other types of seismic waves. We developed a simple processing procedure for single-station three-component seismic data which allows us to select Rayleigh-wave dominated portions. Application of this procedure to data from Southern California led us to confirm that excitation of the secondary-peak microseisms (the predominant energy at about 0.15 Hz) occurs in coastal regions; the source directions, viewed at each station, do not change very much throughout the year. We also discovered that the ratio of the horizontal to vertical amplitudes in Rayleigh waves, termed H/Z in this paper, is shown to have seasonal variations. The H/Z estimates typically reach their maximum in winter and their minimum in summer. Seasonal variations are observed at most stations but peak-to-peak amplitudes of seasonal variations vary greatly from station to station, ranging between 0 and 40 per cent. Two hypotheses were examined to explain this phenomenon; the first hypothesis is that it is caused by seasonal changes in seismic velocities in a layer between the surface and the groundwater level. The second hypothesis is that it is caused by seasonal changes in relative excitation of higher modes compared to dominant fundamental-mode Rayleigh waves. The first hypothesis is not likely, because predicted amplitudes of seasonal variations in H/Z are too small to explain observed variations. The second hypothesis seems quite plausible if source regions move seasonally among regions with different ocean depths. The technique developed in this paper, however, is not sufficient to answer this question conclusively.

Acquisition and Inversion of Dispersive Seismic Waves in Shallow Marine Environments

Two types of dispersive seismic waves have been acquired in different geological settings to investigate the potential to reveal the elastic parameters of the shallow marine subsurface. Scholte waves as well as acoustic guided waves are excited by a near-surface towed airgun, and recorded using two acquisition methods: (1) the towed-acquisition system using a hydrophone streamer towed close to the sea floor, and (2) the stationary-receiver method using Ocean-Bottom Seismometers and/or Hydrophones (OBS/OBH). Our diverse data sets reveal that the spatial sampling of the wavefield required to avoid aliasing may vary significantly for different geological settings. Scholte waves are characterised by a few distinct modes observed at low frequencies and low phase velocities. Their dispersion is mainly controlled by the depth profile of the shear-wave velocity. Acoustic guided waves show profound amplitude variations of numerous higher modes over a broad frequency range. These are sensitive to shear-wave velocity, but more sensitive to compressional-wave velocity than Scholte waves are. To avoid the identification of distinct modes we infer 1-D models of elastic parameters of the subsurface from the inversion of the full wavefield spectra of acoustic guided waves. In the Siberian Laptev Sea we infer the presence of a soft sediment layer (8–10 m) with a well resolved strong S-velocity gradient (150–450 m/s). In the Baltic Sea a low P-velocity layer with a strong vertical gradient (1250–1440 m/s) corresponding to a post-glacial gassy mud layer could be resolved, which agrees well with the sediment stratigraphy derived from a gravity core.

Multimodal Approach to Seismic Pavement Testing

A multimodal approach to nondestructive seismic pavement testing is described. The presented approach is based on multichannel analysis of all types of seismic waves propagating along the surface o...

Energy distribution between seismic waves of different types produced in an elastic half-space by a source with an arbitrary radiation pattern

The energy distribution between different types of seismic waves produced by a source of longitudinal and transverse waves with an arbitrary radiation pattern in an elastic half-space is considered. With an appropriate choice of the angular distribution functions, this source can model an earthquake source. A direct theoretical comparison of the energy distributions of seismic waves generated by an underground explosion and an earthquake is carried out. Analytical relationships that describe the dependence of the energy distribution between different types of waves on the parameters of the medium and the source are derived.

Source bearing estimation using ice-mounted geophones

This paper presents the results of Arctic field trials carried out to estimate the bearing to acoustic sources in the water column using seismo-acoustic particle motion measured at a tri-axial geophone mounted on the sea ice surface. Source bearings are estimated by applying polarization filters to suppress seismic wave types with transverse particle motion, and computing the incident power rotated into radial look angles from 0–360 deg. The 180-deg ambiguity inherent in this rotational analysis is resolved by requiring prograde particle motion in the radial-vertical plane. Results are presented for smooth and rough annual ice and multiyear ice for source ranges from 200 m to 50 km. The results indicate good bearing estimation to long ranges with little dependence on ice type.

Source bearing estimation in the Arctic Ocean using ice-mounted geophones.

This paper investigates the use of geophones mounted on the surface of Arctic sea ice for estimating the bearing to acoustic sources in the water column. The approach is based on measuring ice seismic waves for which the direction of particle motion is oriented radially outward from the source. However, the analysis is complicated by the fact that sea ice supports several types of seismic waves, producing complex particle motion that includes significant nonradial components. To suppress seismic waves with transverse particle motion, seismic polarization filters are applied in conjunction with a straightforward rotational analysis (computation of particle-motion power as a function of angle). The polarization filters require three-dimensional (3D) measurements of particle motion, and apply theoretical phase relationships between vertical and horizontal components for the various waves types. In addition, the 180 degrees ambiguity inherent in the rotational analysis can be resolved with 3D measurements by considering particle motion in the vertical-radial plane. Arctic field trials were carried out involving two components. First, a hammer source was used to selectively excite the various ice seismic waves to investigate their propagation properties and relative importance in bearing estimation. Second, impulsive acoustic sources were deployed in the water column at a variety of bearings and ranges from 200-1000 m. For frequencies up to 250 Hz, source bearings are typically estimated to within an average absolute error of approximately 100.

Seismic anisotropy: tracing plate dynamics in the mantle.

Elastic anisotropy is present where the speed of a seismic wave depends on its direction. In Earth's mantle, elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation. Earthquakes generate two seismic wave types: compressional (P) and shear (S) waves, whose coupling in anisotropic rocks leads to scattering, birefringence, and waves with hybrid polarizations. This varied behavior is helping geophysicists explore rock textures within Earth's mantle and crust, map present-day upper-mantle convection, and study the formation of lithospheric plates and the accretion of continents in Earth history.

Numerical analysis of seismic wave amplification in Nice (France) and comparisons with experiments

The analysis of site effects is very important since the amplification of seismic motion in some specific areas can be very strong. In this paper, the site considered is located in the centre of Nice on the French Riviera. Site effects are investigated considering a numerical approach (Boundary Element Method) and are compared with experimental results. The experimental results are obtained thanks to real earthquakes (weak motion) and microtremor measurements. The investigation of seismic site effects through numerical approaches is interesting because it shows the dependency of the amplification level on such parameters as wave velocity in surface soil layers, velocity contrast with deep layers, seismic wave type, incidence and damping. In this specific area of Nice, experimental measurements obtained for weak motion lead to strong site effects. A one-dimensional (1D) analytical analysis of amplification does not give a satisfactory estimation of the maximum reached levels. A boundary element model is then proposed considering different wave types (SH, P, SV) as the seismic loading. The alluvial basin is successively assumed as an isotropic linear elastic medium and an isotropic linear viscoelastic solid with Zener type behaviour (standard solid). The influence of frequency and incidence is analysed. The thickness of the surface layer, its mechanical properties, its general shape as well as the seismic wave type involved have a great influence on the maximum amplification and the frequency for which it occurs. For real earthquakes, the numerical results are in very good agreement with experimental measurements for each motion component. The boundary element method leads to amplification values very close to the actual ones and much larger than those obtained in the 1D case. Two-dimensional basin effects are then very strong and are well reproduced numerically.

Introduction to seismology

This third edition provides a concise yet approachable introduction to seismic theory, designed as a first course for graduate students or advanced undergraduate students. It clearly explains the fundamental concepts, emphasizing intuitive understanding over lengthy derivations, and outlines the different types of seismic waves and how they can be used to resolve Earth structure and understand earthquakes. New material and updates have been added throughout, including ambient noise methods, shear-wave splitting, back-projection, migration and velocity analysis in reflection seismology, earthquake rupture directivity, and fault weakening mechanisms. A wealth of both reworked and new examples, review questions and computer-based exercises in MATLAB®/Python give students the opportunity to apply the techniques they have learned to compute results of interest and to illustrate Earth's seismic properties. More advanced sections, which are not needed to understand the other material, are flagged so that instructors or students pressed for time can skip them.

Dynamic Buckling Experiments on Liquid Containing Cantilever Cylindrical Shells under Horizontal Excitation.

Dynamic buckling experiments on thin cylindrical shells placed inside a rigid liquid container were carried out by using a shaking table. The shells represent the thermal baffles and the container represents the reactor vessel of a fast breeder reactor. The fluid pressure caused by the horizontal excitation distributes nonuniformly around the cylinders and causes external pressure buckling deformation on them. The buckling pressure on various types of test cylinders and seismic waves was measured, and it was confirmed to be higher than that predicted by static buckling analysis. It was also found that sub harmonic vibration occurs under a certain sinusoidal-wave excitation, and the response displacement increases suddenly at a lower pressure than the buckling pressure measured by seismic-wave-excitation tests. The test results indicated that in seismic design to prevent buckling of the thermal baffles, the static bucklimg analysis can be used as ling as sub-harmonic vibration does not occur.

Listening carefully: unique observations of harmonic tremor at Lascar volcano, Chile

During the deployment of Proyecto de Investigación Sismológica de la Cordillera Occidental 94 (PISCO'94) in the Atacama Desert of Northern Chile, a broadband seismic station and a network of three short-period three-component stations were installed around the active volcano Lascar. The resulting data set includes a sequence of harmonic tremor with a fundamental at about 0.63 Hz and up to 30 overtones lasting 18 h. Power spectra and spectrograms of Lascar's harmonic tremor from the various stations demonstrate that the frequencies recorded cannot be explained as path effects, and must therefore be attributed to mechanisms at or near the source. The polarization of the wavefield cannot simply be explained as the propagation of any of the classical types of seismic waves, thus we apply new methods to the data to investigate the narrowband signals of the harmonic peaks. While the amplitude characteristics of these signals cannot be correlated across the network, frequency characteristics of the harmonic wavefield are consistent across stations and components. The tremor's fundamental frequency changes at the same time at all stations, indicating that such changes must be caused at the source. In addition, a change in the frequency of the fundamental, f1, is reflected exactly in the frequencies of the overtones, nf1 and peak-broadening in the power spectrum is the result of shifts in the fundamental frequency. It is therefore unlikely that the overtones are produced as resonances. This spectral behavior indicates rather that the source is some resonance at a single frequency within the magma, magma/gas or gas parts of the volcano whose amplitude exceeds the range for which the assumptions of linear acoustics are valid.

Seismic anisotropy - a method for studying the fabric of deep continental lithosphere

Independent seismological results, obtained from shear-wave splitting, azimuthal variation of Pn velocities, P-residual spheres and dispersion of surface waves, have demonstrated to observed anisotropies originates in preferred orientation of olivine crystals in the mantle lithosphere. In comparison with oceanic regions, the large-scale fabric of the continental lithosphere is more complex. While the surface-wave data provide an integral property of a number of tectonic units, results on splitting of sub-vertically incident teleseismic shear waves show consistent orientations of the fast S waves within individual lithospheric blocks. In many provinces, the mean azimuth of the fast S polarization parallels the regional geological fabric at the surface (e.g. the strike of a mountain belt). The azimuth-incidence angle dependent terms of teleseismic P-wave residuals, cleared of the effects of source regions and deep mantle paths, show a systematic directional dependence of the relative residuals over distances of several hundred kilometres. Abrupt changes in orientations of the high- and low-velocity directions are related to important tectonic boundaries (deep-seated suture zones). The continental lithosphere related anisotropy scanned by P waves requires a tectonic block structure with dipping high- and low-velocity directions within the lithosphere. Present-day models and interpretations of individual observations of seismic anisotropy depend on the wavelength of different types of seismic waves, as well as on directions of the propagation (both as to azimuths and dips from the horizontal). A joint analysis of body waves - both anisotropic P-residual spheres and shear-wave splitting - allows detecting large-scale anisotropic structures approximated either by hexagonal or orthorhombic symmetries with inclined symmetry axes.

Application of SASW Method Underwater

The spectral analysis of surface waves (SASW) method is a nonintrusive testing technique for determining shear wave velocity (VS) profiles of geotechnical sites using seismic interface waves (also called surface waves). Both small-scale and full-scale experiments have been conducted to develop the SASW technique for use underwater. The small-scale tests were performed to validate theoretical predictions regarding dominant types of seismic waves at the water/substrate interface. The tests clearly show a difference between soft and stiff substrates, where the definition of substrate stiffness is based on the value of the velocity of the Rayleigh-type interface wave (VR) relative to the velocity of compression waves in water (VW). In the simplest case, where the substrate is soft (VR VW), the dominant wave was found to be a generalized Rayleigh wave, the mea...

PEAK STRONG MOTION ATTENUATION RELATIONS FOR HORIZONTAL AND VERTICAL GROUND DISPLACEMENTS

The attenuation of the maximum shear wave for strong ground displacements in large earthquakes (5.4 < Mw <7.2)ia was studied from a seismological viewpoint. Smooth regression curves of attenuation were statistically fitted to measurements made personally on each seismogram. The curves were computed for two different geological classifications of the recording location (rock or soil), and two different fault mechanisms of the seismic source (strike-slip or reverse-fault). The sample consisted of eight strike-slip and four reverse-fault mechanism earthquakes with 237 soil and 92 rock peak ground displacement measurements. The peak ground-motion displacements were measured from the S body-wave portion of the seismograms (frequencies between 0.2 and 1 Hz) after discrimination of the seismic wave types. The peak displacement from any surface wave train was not considered in this analysis. An attenuation distance Hanp was used as the distance from the recording station to the location on the fault plane of largest slip. Two sub-samples were formed consisting of the transverse (SH) and vertical (SV) measurements. The set of ground-displacement attenuation curves predict greater amplitudes at sites classified as soil sites compared to rock sites, and for SH versus SV motion for both types of seismic source mechanisms.

Effects of backfill soils and incident wave types on seismic response of a reinforced retaining wall

Using the finite and infinite element coupled method, the seismic analysis of a reinforced retaining wall has been carried out in this paper. The related numerical results from this study have demonstrated that: (1) the finite and infinite element coupled method is more suitable for the seismic design of a reinforced retaining wall; (2) the stiffness of the backfill soil has a limited effect on the seismic response of the reinforced retaining wall; (3) a vertical seismic P-wave incidence may be the most dangerous condition for the seismic design of a reinforced retaining wall; (4) the types of incident seismic waves have significant effects on the seismic response of a reinforced retaining wall; (5) vertical incident seismic SV-waves and P-waves lead to different patterns of the horizontal acceleration distribution along the height of a reinforced retaining wall.

Imaging Earth's seismic response at long periods

At long periods, seismic waves generated by different earthquakes can be used to construct a single global image of Earth's response to seismic energy. This image (Figure 1) plots the expected ground motion at a point on Earth's surface as a function of time and distance to the earthquake. The various streaks on the plot represent different types of seismic waves, each of which travels at a different speed and arrives at a different time.Stacking—a process that averages and combines seismograms from a number of different source‐receiver locations—was used to create the image from thousands of individual records. The result is a direct view of the average wave field that can be used both as a teaching tool for illustrating the properties of the wave field and as a guide to further study.

Three-dimensional scattering and wave-type conversion by delineated features in a stratified sea bed

The three-dimensional scattering from delineated features in an elastic sea bed, such as faults, small abyssal hills, and extended diapirs, is simulated numerically, and the seismoacoustic wave-type conversion introduced by such reverberant features is addressed. The ocean environment is assumed to be two dimensional: An infinitely long inhomogeneity is imbedded in or penetrating the bottom of an otherwise horizontally stratified ocean. Such reverberant features are assumed to be insonified by an obliquely incident acoustic beam. Due to the fundamental assumption of a two-dimensional environment, this three-dimensional reverberation problem can be treated using Fourier synthesis of 2-D solutions. Here, the two-way solutions are obtained using a modified version of an existing, hybrid wave-number integration-boundary element (WI-BEM) approach [P. Gerstoft and H. Schmidt, J. Acoust. Soc. Am. 89, 1629–1642 (1991)]. This WI-BEM approach inherently decomposes the total field into basic physical components, thus enabling direct identification of the different seismic wave types in the scattered field. The conversion into seismic interface (Scholte) waves and SH waves in the bottom is investigated, and its importance for the bi-static reverberation is discussed. [Work supported by ONR.]