The origin of resonance in the vertical component of earthquakes recorded on soft soil at Wainuiomata, New Zealand

2011 ◽  
Vol 44 (1) ◽  
pp. 19-30
Author(s):  
W. R. Stephenson
Keyword(s):  
New Zealand ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Soft Soil ◽  
Vertical Component ◽  
Soft Water ◽  
Saturated Layer ◽  
Water Saturated

Occasionally-observed resonances in the vertical components of earthquakes recorded at the Wainuiomata, New Zealand, soft site, are likely to be manifestations of the Airy phase of fundamental-mode Rayleigh waves which traverse the site. These packets of waves exist only when a soft, water-saturated layer of soil overlies a substrate with a much higher velocity. Other soft sites in Wellington also show the phenomenon, which may have implications for hazard estimates.

ESTIMATION OF SEISMIC NOISE STRUCTURE USING ARRAYS

Geophysics ◽  
1969 ◽  
Vol 34 (1) ◽  
pp. 21-38 ◽  
Author(s):  
R. T. Lacoss ◽  
E. J. Kelly ◽  
M. N. Toksöz
Keyword(s):  
Spectral Density ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Wave ◽  
Asymptotic Properties ◽  
Vertical Component ◽  
Body Waves ◽  
Low Frequencies ◽  
Short Period

A theoretical study of the use of arrays for the analysis of seismic noise fields has been completed. The frequency‐wavenumber power spectral density [Formula: see text] is defined and techniques for estimating it are given. The estimates require that the auto‐ and crosspower spectral densities be estimated for all elements in the array. Subject to certain asymptotic properties of these auto‐ and crosspower spectral density estimates, expressions for both the mean and variance of the estimates of [Formula: see text] have been obtained. It has been demonstrated that if [Formula: see text] is estimated by the Frequency Domain Beamforming Method, then the estimate has the same stability as the estimates of auto‐ and crosspower spectral density. [Formula: see text] has been estimated from both long‐ and short‐period noise recorded by the Large Aperture Seismic Array in Montana. At frequencies higher than 0.3 Hz, a compressional body‐wave component which correlates with atmospheric disturbances over distant oceans has been detected. In the frequency range of 0.2 and 0.3 Hz both body waves and higher mode Rayleigh waves are observed. At frequencies below 0.15 Hz the organized vertical component of microseisms consists primarily of fundamental mode Rayleigh waves. Appreciable amounts of fundamental mode Love wave energy may also be present on horizontal instruments at these low frequencies.

Quantification of Effects of Ridge and Valley Topography on the Rayleigh Wave Characteristics

2018 ◽  
Vol 12 (03) ◽  
pp. 1850007 ◽  
Author(s):  
J. P. Narayan ◽  
A. Kumar
Keyword(s):  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Large Scale ◽  
Research Work ◽  
Vertical Component ◽  
Staggered Grid ◽  
Long Span ◽  
Shape Ratio ◽  
Day By Day ◽  
Ridge And Valley

The effects of ridge and valley on the characteristics of Rayleigh waves are presented in this paper. The research work carried out has been stimulated by the day by day increase of long-span structures in the hilly areas which are largely affected by the spatial variability in ground motion caused by the high-frequency Rayleigh waves. The Rayleigh wave responses of the considered triangular and elliptical ridge and valley models were computed using a fourth-order accurate staggered-grid viscoelastic P-SV wave finite-difference (FD) program. The simulated results revealed very large amplification of the horizontal component and de-amplification of the vertical component of Rayleigh wave at the top of a triangular ridge and de-amplification of both the components at the base of the triangular valley. The observed amplification of both the components of Rayleigh wave in front of elliptical valley was larger than triangular valley models. A splitting of the Rayleigh wave wavelet was inferred after interaction with ridge and valley. It is concluded that the large-scale topography acts as a natural insulator for the surface waves and the insulating capacity of the valley is more than that of a ridge. This insulation phenomenon is arising due to the reflection, diffraction and splitting of the surface wave while moving across the topography. It is concluded that insulating potential of the topography for the Rayleigh waves largely depends on their shape and shape-ratio.

Detection of interfering Rayleigh waves at LASA

1971 ◽  
Vol 61 (4) ◽  
pp. 807-849
Author(s):  
Jack Capon ◽  
Jack F. Evernden
Keyword(s):  
Rayleigh Wave ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Detection Method ◽  
Wave Number ◽  
Continental Margins ◽  
S Waves ◽  
Analysis Technique ◽  
Multiple Paths ◽  
Back Azimuth

abstract The problem of detecting one Rayleigh wave in the presence of the coda of another larger Rayleigh wave is considered. A detection method is proposed in which a high-resolution, wave number analysis technique is applied to prefiltered data from the Large Aperture Seismic Array (LASA) to determine the direction of arrival of the 40-sec-period Rayleigh-wave group at the appropriate arrival time. The performance of this detection method is considered in great detail. A necessary concomitant of the study of the detection method is the determination of the phases which comprise the coda. It is shown that one component of the coda consists of fundamental-mode Rayleigh waves which propagate along multiple paths and may be caused by either reflections at continental margins or diffraction effects. As has been demonstrated many times, the coda is shown to consist also of fundamental-mode Rayleigh waves which have propagated around the Earth in the direction of the back azimuth. Multiply reflected P and S waves, which propagate primarily in the upper mantle, are detected easily.

Enhancing Signal-to-Noise Ratios of High-Frequency Rayleigh Waves Extracted from Ambient Seismic Noises in Topographic Region

2020 ◽  
Vol 110 (2) ◽  
pp. 793-802
Author(s):  
Ping Ping ◽  
Risheng Chu ◽  
Yu Zhang ◽  
Jun Xie
Keyword(s):  
Free Surface ◽  
Correlation Functions ◽  
High Frequency ◽  
Rayleigh Waves ◽  
Vertical Component ◽  
Noise Correlation ◽  
Surface Boundary ◽  
Elastic Wedge ◽  
Signal To Noise ◽  
Surface Boundary Conditions

ABSTRACT High-frequency Rayleigh waves can be extracted from ambient seismic noises through noise correlation functions (NCFs), which provides a useful tool to image shallow structures in topographic regions, for example, landslides. Topography may affect signal-to-noise ratios (SNRs) of extracted Rayleigh waves. It is necessary to investigate the propagation features of Rayleigh waves passing a 3D topography. Based on the incident and scattered waves satisfying the free surface boundary conditions, we first derive the displacement responses of Rayleigh waves across a 3D elastic wedge. The results show that the particle motions of Rayleigh waves are an ellipse whose longer axis is always perpendicular to the topographic free surface. Therefore, the Qg component, perpendicular to the topographic free surface, is a better choice to extract high-frequency Rayleigh waves than the conventional vertical component. To verify the choice, we carry out numerical simulations to extract high-frequency NCFs for a typical 3D massif model. Finally, we apply this approach to extract high-frequency Rayleigh-wave NCFs on the Xishancun landslide in southwestern China. The NCFs obtained using the Qg component have more coherent waveforms and higher SNRs than those using the vertical component. We conclude that the Qg component has advantages in extracting high-frequency Rayleigh waves over the conventional vertical component.

scholarly journals Characteristics of the horizontal component of Rayleigh waves in multimode analysis of surface waves

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. EN1-EN11 ◽  
Author(s):  
Tatsunori Ikeda ◽  
Toshifumi Matsuoka ◽  
Takeshi Tsuji ◽  
Toru Nakayama
Keyword(s):  
Surface Waves ◽  
Wave Velocity ◽  
Rayleigh Waves ◽  
Field Data ◽  
Vertical Component ◽  
Dispersion Curves ◽  
Horizontal Component ◽  
S Wave ◽  
Higher Modes ◽  
Explosive Source

In surface-wave analysis, S-wave velocity estimations can be improved by the use of higher modes of the surface waves. The vertical component of P-SV waves is commonly used to estimate multimode Rayleigh waves, although Rayleigh waves are also included in horizontal components of P-SV waves. To demonstrate the advantages of using the horizontal components of multimode Rayleigh waves, we investigated the characteristics of the horizontal and vertical components of Rayleigh waves. We conducted numerical modeling and field data analyses rather than a theoretical study for both components of Rayleigh waves. As a result of a simulation study, we found that the estimated higher modes have larger relative amplitudes in the vertical and horizontal components as the source depth increases. In particular, higher-order modes were observed in the horizontal component data for an explosive source located at a greater depth. Similar phenomena were observed in the field data acquired by using a dynamite source at 15-m depth. Sensitivity analyses of dispersion curves to S-wave velocity changes revealed that dispersion curves additionally estimated from the horizontal components can potentially improve S-wave velocity estimations. These results revealed that when the explosive source was buried at a greater depth, the horizontal components can complement Rayleigh waves estimated from the vertical components. Therefore, the combined use of the horizontal component data with the vertical component data would contribute to improving S-wave velocity estimations, especially in the case of buried explosive source signal.

scholarly journals Rayleigh Waves Transformation in Liquefying Water-saturated Sands

2016 ◽  
Vol 63 (2-3) ◽  
pp. 173-190
Author(s):  
Ryszard Staroszczyk
Keyword(s):  
Rayleigh Waves ◽  
Granular Media ◽  
Ground Motions ◽  
Soil Liquefaction ◽  
Saturated Sand ◽  
Rayleigh Surface Waves ◽  
Pore Pressures ◽  
Sand Deposit ◽  
Water Saturated ◽  
Excess Pore Pressures

AbstractThe behaviour of a water-saturated sand deposit subjected to dynamic loads induced by the propagation of Rayleigh surface waves is analysed. Cyclic shearing of the saturated sand matrix due to ground motions results in the development of excess pore pressures in the soil and its subsequent liquefaction. The phenomena of pore pressure generation and soil liquefaction are investigated within the framework of a compaction theory for saturated granular media. The results of calculations, carried out by a finite-element method, illustrate the evolution of pore pressures and the development of liquefaction zones in the soil, and show the variation of surface wave parameters with the progressive degradation of the strength of the subsoil.

A new method to determine phase velocities of Rayleigh waves from microseisms

Geophysics ◽  
2004 ◽  
Vol 69 (6) ◽  
pp. 1535-1551 ◽  
Author(s):  
Ikuo Cho ◽  
Taku Tada ◽  
Yuzo Shinozaki
Keyword(s):  
Rayleigh Waves ◽  
Vertical Component ◽  
Field Tests ◽  
Spectral Ratio ◽  
New Method ◽  
Phase Velocities ◽  
Seismic Sensors ◽  
Time Histories ◽  
Theoretical Considerations ◽  
Incoherent Noise

We have developed a new method to determine phase velocities from the vertical component of microseisms recorded with an array of seismic sensors spaced around the circumference of a circle. We calculate two different time histories by taking the average of the seismograms with differing sets of weights for the sensor stations. The spectral ratio of these two time histories contains no information on the arrival directions or on the amplitudes of the incoming waves but depends solely on the phase velocities of the arriving modes. Theoretical considerations indicate that the effects of directional aliasing caused by the use of a finite number of sensors in the field implementation of our method are small in most situations except for short wavelengths. The presence of incoherent noise limits the efficacy of our method for long wavelengths. In field tests using arrays of three seismic sensors, we obtained appropriate estimates of phase velocities in the wavelength range from 5r to 30r where r, the array radius, was on the order of a few meters.

Structure of microseismic waves: estimation of direction of approach by comparison of vertical and horizontal components

1954 ◽  
Vol 223 (1152) ◽  
pp. 96-111 ◽  
Keyword(s):  
Rayleigh Waves ◽  
Vertical Component ◽  
Correlation Coefficients ◽  
Love Waves ◽  
The North ◽  
Wave Interference ◽  
Rayleigh And Love Waves ◽  
The Mean ◽  
East West ◽  
Phase Differences

Analysis of microseisms recorded at Kew Observatory on 8 to 10 October 1951 affords further confirmation of the wave-interference theory of microseism generation, and allows those of 8 to 10 October to be attributed to a fast-moving depression between the Azores and Iceland. Although the bearing of the microseism-generating area changes by more than 90° during the period investigated, there is no appreciable difference in the ratio of the mean ampli­tudes of the north-south and east-west horizontal components as would be expected if the microseisms consisted entirely of Rayleigh waves. An investigation of the phase differences between the three components, using Lee’s method, suggests that the microseisms consist of Rayleigh and Love waves in comparable proportions. Making use of this assumption, the vertical component, which is not affected by the Love waves, is correlated with the two horizontal components with an electronic correlating device, and the bearing of the microseism area can be deduced from the correlation coefficients. The calculated bearings agree reasonably well with those obtained from the meteorological charts. The bearing of a storm on 12 to 15 November 1945, studied in a previous paper, was also calculated satisfactorily.

scholarly journals Frequency dependent amplification of weak ground motions in Porirua and Lower Hutt, New Zealand

1992 ◽  
Vol 25 (4) ◽  
pp. 303-331 ◽  
Author(s):  
J. John Taber ◽  
Euan G. C. Smith
Keyword(s):  
New Zealand ◽  
Frequency Band ◽  
Spectral Ratio ◽  
Silty Sand ◽  
Peak Ground Velocity ◽  
Soft Sediment ◽  
Spectral Ratios ◽  
Near Surface ◽  
Fine Grained ◽  
Water Saturated

The relative ground response due to microearthquakes has been examined at a total of 36 sites in the Porirua and Lower Hutt regions of New Zealand, as part of a multi-disciplinary microzoning project conducted with the Wellington Regional Council. The sites were studied in two separate experiments and were chosen to sample a variety of soil types and depths ranging from strong rock to thick sections of alluvial gravels and sands to soft water-saturated fine-grained deposits. The amplitude response of each site relative to a bedrock reference site has been determined as a function of frequency. Fourier spectral ratios (Fsr) were calculated for each earthquake and then between three and twenty-six earthquakes were averaged together at each of the sites. Spectral ratios of individual earthquakes varied significantly from the average spectral ratio. In the Hutt Valley there is a gradual down-valley increase in shaking in a similar pattern to the down-valley increase of the depth to bedrock and thickness of near-surface soft sediment. The response at the upper-most valley sites, underlain by less than 50 m of alluvial gravel and silty sand, is similar to the response at the rock sites on the side of the valley (Fsr = 2.4) while the Fourier spectral ratios reach 14 at the lower-most valley sites, which are underlain by greater than 20 m of soft sediment. The highest amplifications were recorded at two sites on soft flexible sediments (10 to 35 m thick) in an enclosed valley (Fsr = 16 to 18) and a site on an apparently drained and filled swamp (Fsr = 15). A spectral ratio of 18 corresponds to an increase in peak ground velocity by a factor of 5. The amplification at most Lower Hutt sites occurred over a broad frequency band from 0.5 Hz to up to 5 Hz, with the high frequency limit of the band decreasing as the spectral ratio in the band increased. Two of the flexible sediment sites exhibited a very narrow frequency response with a peak in the 1-2 Hz range, similar to three flexible sediment sites in the Porirua basin where the amplification was in the 1-3 Hz frequency band. These flexible sediment sites had Fourier spectral ratios of up to 18 relative to a hard rock site. Three other Porirua sites had spectral ratios greater than 5 at some frequency. Two of these sites were on fan alluvium and fine grained sediment, while the third was on siltly sand on a topographic ridge. The remaining five sites were on weathered gravels and showed little amplification.

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