共查询到20条相似文献，搜索用时 15 毫秒
1.
Sukhendu Dey 《Pure and Applied Geophysics》1971,90(1):38-52
Summary In this paper, the frequency equation for phase velocity of waves propagated in a laminated medium consisting of two eleastic layers of finite thickness under initial stresses, has been obtained. It has been shown that when wave length becomes very small compared to the thickness of each layer, the wave approaches two Rayleigh waves at the two outer surfaces with the possibility of Stoneley waves at the interface. The propagation ofSH-waves in the composite medium under initial stresses has also been discussed. A particular case has been taken to find the velocity of Love wave in the homogeneous half space under initial compressive stresses.Biot's incremental deformation theory has been used. 相似文献
2.
Arabinda Biswas 《Pure and Applied Geophysics》1969,76(1):100-106
Summary The propagation ofSH-waves in a vosco-elastic layer having variable material properties has been studied to explain the damping phenomenon of the wave motion. The damping coefficient may be calculated and the effect of heterogeneity on such type of wave motion may be observed from the obtained frequency equation. 相似文献
3.
I. Lerche 《Pure and Applied Geophysics》1987,125(5):717-751
We demonstrate how multiples, generated at the interfaces of plane parallel beds, modify the propagation characteristics of an originally coherent seismic wave. For waves propagating at an angle to the bedding plane we find that theSV andP-waves couple so that neither is a pure mode. TheSH-wave, while modified in its propagation characteristics by multiples, remains a pure mode. The coupling ofSV-multiples into the quasi-P-mode appears weaker than the coupling ofP-wave multiples into the quasi-SV mode; at least this is so for the two simple cases of (a) density fluctuations only and (b) correlatedV
p
andV
s
fluctuations which conserve Poisson's ratio.We also find that the coupling is sensitive to both the angle of propagation and frequency. In addition there is a cut-off angle forP-wave multiples influencing the quasi-SV mode. Propagation angles larger than the cut-off permit theP-multiples to modify the phase of the quasi-SV mode, but not its effective attenuation. No such cut-off effect is found for SV-multiples influencing the quasi-P mode, whose angle-dependent and frequency-dependent phase distortion and effective attenuation are influenced both byP-wave multiples andSV-multiples.In view of the mathematical complexity of the expressions describing the phase, and effective attenuation of modes when allowance is made forP-andS-wave multiples, we strongly advocate numerical coding of the major mathematical formulae. By so doing a systematic study can be undertaken of the frequency and offset dependence of seismic waves as a function of seismic source input and power spectral behavior of the fluctuations in density and elastic constants of beds. It is our opinion that the full mathematical expressions are too involved to permit an analytic, systematic investigation to be given of the phase and attenuation of seismic waves with any degree of sophistication or generality. 相似文献
4.
In this paper, we have considered the reflection and refraction of a plane wave at an interface between two half-spaces. The
lower half-spaces is composed of highly anisotropic triclinic crystalline material and the upper half-space is homogeneous
and isotropic. It has been assumed that due to incidence of a plane quasi-P (qP) wave, three types of waves, namely, quasi-P (qP), quasi-SV (qSV) and quasi-SH (qSH), will be generated in the lower half space whereas P and S waves will be generated in the upper half space. The phase velocities of all the quasi waves have been calculated. It has
been assumed that the direction of particle motion is neither parallel nor perpendicular to the direction of propagation.
Some specific relations have been established between directions of motion and propagation, respectively. The expressions
for reflection coefficients of qP, qSV, qSH and refracted coefficients of P and SV waves are obtained. Results of reflection and refraction coefficients are presented. 相似文献
5.
Subhash Chandra Ghosh 《Pure and Applied Geophysics》1968,70(1):22-27
Summary ApplyingWiener-Hopf techniques the diffraction ofSH-waves originating from a moving point source due to the presence of a step change in the elevation of the surface of a homogeneous half-space have been obtained. An interesting feature of resonance associated with the motion of a load at a velocityv
0
–1 approachingv
0
–1 has been observed. 相似文献
6.
A. J. Willson 《Pure and Applied Geophysics》1973,110(1):1977-1981
Summary A theoretical study is made of the propagation ofSH waves of small amplitude in an infinite elastic plate subjected to a primary normal stress. It is shown that the effect of the stress may be represented by a re-scaling of the plate thickness, provided that one elastic constant is also redefined suitably. 相似文献
7.
A layeredP- andS-wave velocity model is obtained for the Friuli seismic area using the arrival time data ofP- andS-waves from local earthquakes. A damped least-squares method is applied in the inversion.The data used are 994P-wave arrival times for 177 events which have epicenters in the region covered by the Friuli seismic network operated by Osservatorio Geofisico sperimentale (OGS) di Trieste, which are jointly inverted for the earthquake hypocenters andP-wave velocity model. TheS-wave velocity model is estimated on the basis of 978S-wave arrival times and the hypocenters obtained from theP-wave arrival time inversion. We also applied an approach thatP- andS-wave arrival time data are jointly used in the inversion (Roecker, 1982). The results show thatS-wave velocity structures obtained from the two methods are quite consistent, butP-wave velocity structures have obvious differences. This is apparent becauseP-waves are more sensitive to the hypocentral location thanS-waves, and the reading errors ofS-wave arrival times, which are much larger than those ofP-waves, bring large location errors in the joint inversion ofP- andS-wave arrival time. The synthetic data tests indicated that when the reading errors ofS-wave arrivals are larger than four times that ofP-wave arrivals, the method proposed in this paper seems more valid thanP- andS-wave data joint inversion. Most of the relocated events occurred in the depth range between 7 and 11 km, just above the biggest jump in velocity. This jump might be related to the detachment line hypothesized byCarulli et al. (1982). From the invertedP- andS-wave velocities, we obtain an average value 1.82 forV
p
/V
s
in the first 16 km depth. 相似文献
8.
R. K. Chadha 《Pure and Applied Geophysics》1994,142(2):319-328
T phases of three earthquakes from the Indian Ocean region, recorded by a short-period vertical-component seismic station network located in the vicinity of Kanyakumari on the southernmost tip of India, are studied. Two of these earthquakes are located west of 90°E ridge and one in the Nicobar Island region. However, seven other earthquakes which occurred 150–200 km south of Kanyakumari in the ocean did not produceT phases. An analysis ofT-waves (tertiary waves) travel time reveals the zone ofP-wave toT-wave conversion (i.e.,PT phase) region to coincide with the western continental slope of Srilanka. Further, it is observed that the disposition of the bathymetry between Srilanka and southern India strongly favours the downslope propagation mechanism ofT-wave travel to the southern coast of India through SOFAR channel. These observations are reported for the first time from India. 相似文献
9.
K. A. Berteussen 《Pure and Applied Geophysics》1977,115(3):707-719
Using simulated data, it is demonstrated that one may estimate the body wave velocity in the crust by measuring the angle of incidence ofP-waves provided only the very first part of the signal is used. This angle has been measured for a set ofP-waves at the NORSAR long period instrument sites. Combining these observations with measurements of apparent velocities, we find that the data indicates a crust velocity of 6.1±0.4 km/sec. While it is somewhat uncertain to what depth the value is representative, the observations are in obvious disagreement with previous authors who concluded that long periodP-waves were not affected by the earth's crust. Because of difficulties in separating the effects of real velocity variations from measurement errors, the details of the observedP-wave variation across the array are difficult to interpret. The consistent behavior of the data does, however, indicate that variations of approximately 3% must exist in the crustalP-wave velocity across the array. 相似文献
10.
Leonardo Alvarez Julio García Franco Vaccari Giuliano F. Panza Bertha González Carmen Reyes Bárbara Fernández Ramón Pico José A. Zapata Enrique Arango 《Pure and Applied Geophysics》2004,161(5-6):1041-1059
— The expected ground motion in Santiago de Cuba basin from earthquakes which occurred in the Oriente fault zone is studied. Synthetic SH-waves seismograms have been calculated along four profiles in the basin by the hybrid approach (modal summation for the path source-profile and finite differences for the profile) for a maximum frequency of 1 Hz. The response spectra ratio (RSR) has been determined in 49 sites, distributed along all considered profiles with a spacing of 900 m. The corresponding RSR versus frequency curves have been classified using a logical-combinatorial algorithm. The results of the classification, in combination with the uppermost geological setting (geotechnical information and geological geometry of the subsoil) are used for the seismic zoning of the city. Three different main zones are identified, and a small sector characterized by major resonance effects, due to the particular structural conditions. Each zone is characterized in terms of its expected ground motion parameters for the most probable strong earthquake (MS=7), and for the maximum possible (MS=8). 相似文献
11.
Summary Underwater sound waves from earthquakes or so-calledT-waves are investigated for the Atlantic-Arctic area for the years 1953–1968, mainly from Swedish seismograph records, and for comparison also from an earthquake in the equatorial Atlantic withT-waves recorded on both sides of the ocean. The waves travel as sound waves through water, and asPg, Sg andRg over the land path. The North Atlantic source area of theT-waves, recorded at Scandinavian stations, is very well limited in extent with a strong concentration northeast of Jan Mayen, probably due to favourable bottom topography. The calculated sound velocities in water are 1.43 km/sec for the Arctic case and 1.52 km/sec for the equatorial one. TheT-waves exhibit a clear inverse dispersion. The dispersion explains their long duration. The duration of theT-phase increases logarithmically with the maximum amplitudes within theT-wave group and decreases linearly with distance over the land path, corresponding to a quality factor of about 700. Propagation across the ocean by multiple reflections between surface and bottom appears as the most probable mechanism. The particle motion ofT Sg is dominantly transverse horizontal, which is explained by refraction when the waves are transmitted to land. TheT-wave spectra at two different localities show clear relations, depending upon the ocean depths. 相似文献
12.
Jayanta Bhattacharya 《Pure and Applied Geophysics》1969,72(1):61-71
Summary The conditions under which Love type ofSH waves can propagate in a non-homogeneous internal stratum of finite depth lying between two semi-infinite isotropic elastic media are considered in this paper. Two types of non-homogeneity have been studied, in one case the rigidity is supposed to vary exponentially with depth while the density remains constant and in the other both rigidity and density are assumed to vary linearly with depth. 相似文献
13.
Propagation of magneto-elastic waves in a perfectly conducting plate extending to infinity in vacuum
C. M. Purushothama 《Pure and Applied Geophysics》1965,61(1):60-68
Summary The effects of a uniform external magnetic field on the propagation of waves in a homogeneous, infinitely conducting flat plate with free boundaries have been studied. It has been found that in general all the three types of waves —P, SV andSH waves—are coupled and the influence may be more pronounced in coupling the symmetric and antisymmetric types of motions in every mode.When the magnetic field is parallel to the plane faces and transverse to the direction of wave propagation, the shear wave polarized parallel to the field is purely elastic whereas the coupledP andS V waves are magnetoelastic and exhibit dispersion strikingly similar to the non-magnetic case, provided the electro-magnetic radiation into the surrounding free space is neglected.The results reported in an earlier communication [1]2) are also confirmed. 相似文献
14.
We present an efficient scheme to compute high-frequency seismograms (up to 10 Hz) forSH-waves in a horizontally stratified medium with the mode summation method. The formalism which permits the computation of eigenvalues, eigenfunctions and related integral quantities is discussed in detail. Anelasticity is included in the model by using the variational method. Phase velocity, group velocity, energy integral and attenuation spectra of a structure enable the computation of complete strong motion seismograms, which are the basic tool for the interpretation of near-source broad-band data.Different examples computed for continental structures are discussed, where one example is the comparison between the observed transversal displacement recorded at station IVC for the November 4, Brawley 1976 earthquake and synthetic signals. In the case of a magnitudeM
L
=5.7 earthquake in the Friuli seismic area we apply the mode summation method to infer from waveform modeling of all three components of motion of observed data some characteristics of the source.On leave from Institute of Geophysics, ETH, Zürich, Switzerland. 相似文献
15.
Marijan Dravinski 《地震工程与结构动力学》2003,32(5):653-670
Scattering of plane harmonic waves by a three‐dimensional basin of arbitrary shape embedded within elastic half‐space is investigated by using an indirect boundary integral equation approach. The materials of the basin and the half‐space are assumed to be the most general anisotropic, homogeneous, linearly elastic solids without any material symmetry (i.e. triclinic). The unknown scattered waves are expressed in terms of three‐dimensional triclinic time harmonic full‐space Green's functions. The results have been tested by comparing the surface response of semi spherical isotropic and transversely isotropic basins for which the numerical solutions are available. Surface displacements are presented for a semicircular basin subjected to a vertical incident plane harmonic pseudo‐P‐, SV‐, or SH‐wave. These results are compared with the motion obtained for the corresponding equivalent isotropic models. The results show that presence of the basin may cause significant amplification of ground motion when compared to the free‐field displacements. The peak amplitude of the predominant component of surface motion is smaller for the anisotropic basin than for the corresponding isotropic one. Anisotropic response may be asymmetric even for symmetric geometry and incidence. Anisotropic surface displacement generally includes all three components of motion which may not be the case for the isotropic results. Furthermore, anisotropic response strongly depends upon the nature of the incident wave, degree of material anisotropy and the azimuthal orientation of the observation station. These results clearly demonstrate the importance of anisotropy in amplification of surface ground motion. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
16.
Biot's theory is employed to study the reflection and transmission ofSH waves in a sandy layer lying over a fluid-saturated porous solid half-space. The entire medium is considered under constant initial stress. Effects of sandiness, initial stress, anelasticity and viscosity of the interstitial fluid on the partitioning of energy are studied. In the presence of initial stress the incident wave starts attenuating when incider beyond a certain angle (depending upon the amount of initial stress), even if the medium is perfectly clastic. Anelasticity of the solid layer results in the dissipation of energy during transmission. The direction of attenuation vector of incident wave affects the dissipation energy to a large extent. Effect on partitioning of energy reverse at incidence after the critical angle. A complete account of energy returmed back to the underlying half-space and that which is dissipated in the overlying layer has been discussed analytically as well as numerically. 相似文献
17.
Subhas Dutta 《Pure and Applied Geophysics》1966,64(1):9-13
Summary The effect on the propagation of love waves in a density stratified crust of finite thickness lying on a homogeneous half space is studied in this paper. Variations of phase and group velocities with wave number are obtained and the result is compared with that ofWilson. 相似文献
18.
We theoretically study the scattering ofP, SV andSH waves by a zonal distribution of cracks, which simulates a fault fracture zone. An investigation is conducted how the geometrical properties of the crack distribution and the frictional characteristics of the crack surface are reflected in the attenuation and dispersion of incident waves, as well as in the amplitudes of the transmitted and reflected waves from the zone. If the crack distribution within the fault zone changes temporally during the preparation process of the expected earthquake, it will be important for earthquake prediction to monitor it, utilizing the scattering-induced wave phenomena.We consider the two-dimensional problem. Aligned cracks with the same length are assumed to be randomly distributed in a zone with a finite width, on which elastic waves are assumed to be incident. The distribution of cracks is assumed to be homogeneous and sparse. The crack surface is assumed to be stress-free, or to undergo viscous friction; the latter case simulates fluid-filled cracks. The opening displacement of the crack is assumed to be negligibly small. The idea of the mean wave formalism is employed in the analysis, and Foldy's approximation is assumed.When the crack surface is stress-free, it is commonly observed for every wave mode (P, SV andSH) that the attenuation coefficientQ
–1 peaks aroundka1, the phase velocity is almost independent ofk in the rangeka<1 and it increases monotonically withk in the rangeka>1, wherek is the intrinsicS wavenumber anda is the half length of the crack. The effect of the friction is to shift the peak ofQ
–1 and the corner of the phase velocity curve to the low wavenumber range. The high wavenumber asymptote ofQ
–1 is proportional tok
–1 independently of model parameters and the wave modes. If the seismological observation thatQ
–1 ofS waves has a peak at around 0.5 Hz in the earth's crust is combined with our results, the upper limit of crack size within the crust is estimated about 4 km. The information regarding the transmitted and reflected waves, such as the high wavenumber limit of the amplitude of the transmitted wave etc., allows estimation of the strength of the friction. 相似文献
19.
A. R. Banghar 《Pure and Applied Geophysics》1970,82(1):46-54
Summary The dispersion ofSH body waves in a continously stratified isotropic medium is studied theoretically. Limiting forms of the displacement are given for zero, small and large values of the horizontal component of the wave number. It has been shown that below a certain characteristic frequency the dependence of the displacement on the distance from the free surface is monotonic instead of periodic. 相似文献
20.
The dynamic response of a finite number of flexible surface foundations subjected to harmonic incident Rayleigh or SH waves is presented. The foundations are assumed to be resting on an elastic half-space. The results show that the foundation stiffness has a marked effect on the vertical response, while there is only a minor effect on the horizontal displacements. In general, the dynamic response decreases with increasing foundation stiffness. In cases of Rayleigh wave incidence, the existence of an adjacent foundation generates a certain amount of horizontal response in the direction perpendicular to the incident wave and subsequently causes the system to undergo a torsional motion; while in cases of horizontally incident SH waves, a vertical response has been observed and its magnitude is comparable to the response in the direction of the incident wave. 相似文献