scholarly journals Attenuation of shear waves in the upper and lower mantle

1964 ◽  
Vol 54 (6A) ◽  
pp. 1855-1864 ◽  
Author(s):  
Robert L. Kovach ◽  
Don L. Anderson
Keyword(s):  
Lower Mantle ◽  
Seismic Waves ◽  
Wave Amplitude ◽  
Body Wave ◽  
Shear Waves ◽  
Normal Incidence ◽  
Frequency Range ◽  
Spectral Ratios ◽  
The Earth ◽  
Deep Focus

abstract The attenuation of seismic waves is a direct measure of the absorption due to nonelastic processes in the earth. The well known difficulties in obtaining body wave amplitude decrement data have been avoided by studying the spectral ratios of multiple ScS and sScS phases from two deep focus earthquakes recorded at near normal incidence. The average Q, for shear, in the mantle is about 600 for the frequency range 0.015 to 0.07 cps. Assuming that equal radiation occurs upwards and downwards from the source the average Q for the upper 600 km of the mantle is determined to be about 200 and about 2200 for the rest of the mantle. The value for Q at the base of the mantle is at least 5000 for shear waves.

Two-parameter scaling of source spectra: Love waves from deep-focus Bonin Islands earthquakes

1977 ◽  
Vol 67 (2) ◽  
pp. 285-300
Author(s):  
R. James Brown
Keyword(s):  
Body Wave ◽  
Scaling Law ◽  
Spectral Ratio ◽  
Love Waves ◽  
Corner Frequency ◽  
Spectral Ratios ◽  
Bonin Islands ◽  
Deep Focus ◽  
Two Parameter ◽  
Fault Length

Abstract Starting with the one-parameter scaling law of Aki, a two-parameter expression is developed to model the source factor of the far-field spectrum from a dislocation fault source for both ω−2 and ω−3 high-frequency asymptotic types. Aki's assumption of similarity is relaxed in two respects: it is neither here assumed that wD0 ∞ L2 (L = fault length, w = fault width, D0 = average dislocation) nor that kT = v kL (kT−1 = correlation time, kL−1 = correlation length, v = velocity of rupture propagation), the latter being equivalent to allowing for Brune's fractional stress drop. From this two-parameter model a four-parameter model of spectral ratio is obtained and fitted to observed spectral ratios by computer optimization of the four parameters. Observed spectral ratios have been determined from the Love waves recorded at NORSAR from six deep-focus Bonin Islands earthquakes using a common-path method. From the optimal values of the four parameters, values are determined for corner frequency (f ≈ 0.2 Hz for m 6.0; f ≈ 0.3 Hz for m = 5.3; m = PDE body-wave magnitude), relative fault length, relative seismic moment (and magnitudes), and p, the slope of the corner-frequency locus. Values found for p are all greater than 3 and such p, in combination with an ω−3 scaling law, can yield a reasonable m:M relation, i.e., with no ceiling imposed on m. A slightly better fit is obtained by starting with an ω−3 model than with ω−2.

scholarly journals Sir Harold Jeffreys, 2 April 1891 - 18 March 1989

1990 ◽  
Vol 36 ◽  
pp. 301-333 ◽  
Keyword(s):  
Small Group ◽  
20Th Century ◽  
Lower Mantle ◽  
Seismic Waves ◽  
Classical Mechanics ◽  
The Core ◽  
New Methods ◽  
The Earth ◽  
Physical Study ◽  
Primitive Condition

Harold Jeffreys stood out among the small group of pioneers who developed the physical study of the Earth from its primitive condition at the beginning of the 20th century to its state at the launch of the first Sputnik . He, above all, applied classical mechanics to investigate the interior of the Earth. He showed that the core of the Earth is liquid and that there is a substantial difference between the upper and lower mantle, as we now call them. His massive analyses of travel times of seismic waves (with K.E. Bullen, F.R.S.) are still standards of reference and are currently being brought up to date. Jeffreys retired from his Chair at Cambridge (but certainly not from active study) just after the first Sputnik had been launched, and as powerful new methods in seismology and marine geophysics were coming into use. Geophysics has since expanded out of all recognition so that it is easy to lose sight of Jeffreys’s earlier contributions. There have been considerable changes in the concepts and methods of geophysics from some that he established, yet the major spherically symmetrical elements of the structure of the Earth that he did so much to elucidate, are the basis for all subsequent elaboration, and generations of students learnt their geophysics from his book The Earth .

P-wave amplitude variation with epicentral distance and the magnitude relations

1975 ◽  
Vol 65 (4) ◽  
pp. 915-926
Author(s):  
K. L. Kaila ◽  
Dipankar Sarkar
Keyword(s):  
Lower Mantle ◽  
Wave Amplitude ◽  
Epicentral Distance ◽  
P Wave ◽  
Amplitude Variation ◽  
Distance Range ◽  
Nuclear Explosions ◽  
The Earth ◽  
Shallow Earthquakes ◽  
Discontinuous Nature

Abstract Investigation of the variation of P-wave amplitudes and d2T/dΔ2 with epicentral distance reveals that the amplitudes in the distance range up to 100° can be represented by seven discontinuous curves. The discontinuous nature of the amplitude curves can be explained due to the possible existence of first- or second-order velocity discontinuities in the upper and lower mantle of the Earth. Seven magnitude relations corresponding to these amplitude curves are given, which yield consistent magnitudes for nuclear explosions as well as for shallow earthquakes.

SEISMIC WAVES FROM A HORIZONTAL FORCE

Geophysics ◽  
1956 ◽  
Vol 21 (3) ◽  
pp. 715-723 ◽  
Author(s):  
J. E. White ◽  
S. N. Heaps ◽  
P. L. Lawrence
Keyword(s):  
Surface Waves ◽  
Shear Wave ◽  
Qualitative Agreement ◽  
Seismic Waves ◽  
Shear Waves ◽  
Earth Surface ◽  
Horizontal Force ◽  
The Earth ◽  
Fundamental Research ◽  
The Waves

As part of a program of fundamental research on seismic waves, a generator was built for applying a transient horizontal force at the surface of the ground and the resulting seismic waves were observed in some detail. The force is applied when a mass swinging through an arc strikes a target anchored to the earth. Surface geophones along a line in the direction of the force register vertically polarized shear waves refracted back up to the surface, whereas geophones on a line perpendicular to the force register horizontally polarized shear waves. The speeds of the two types of shear waves are often different, indicating anisotropy. Geophones buried below the target show a down‐going shear wave. Variation of amplitude with angle, and other features, are in qualitative agreement with the results given by Rayleigh and others for the waves due to a force at a point in an infinite solid. Love waves and other surface waves were observed, which of course would not be expected from an nterior force.

scholarly journals Rapid estimation of tsunami earthquake magnitudes at local distance

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Akio Katsumata ◽  
Masayuki Tanaka ◽  
Takahito Nishimiya
Keyword(s):  
Magnitude Estimation ◽  
Seismic Wave ◽  
Seismic Waves ◽  
Wave Amplitude ◽  
Amplitude Distribution ◽  
Distribution Method ◽  
Finite Fault ◽  
Tsunami Earthquakes ◽  
Tsunami Earthquake ◽  
The Moment

AbstractA tsunami earthquake is an earthquake event that generates abnormally high tsunami waves considering the amplitude of the seismic waves. These abnormally high waves relative to the seismic wave amplitude are related to the longer rupture duration of such earthquakes compared with typical events. Rapid magnitude estimation is essential for the timely issuance of effective tsunami warnings for tsunami earthquakes. For local events, event magnitude estimated from the observed displacement amplitudes of the seismic waves, which can be obtained before estimation of the seismic moment, is often used for the first tsunami warning. However, because the observed displacement amplitude is approximately proportional to the moment rate, conventional magnitudes of tsunami earthquakes estimated based on the seismic wave amplitude tend to underestimate the event size. To overcome this problem, we investigated several methods of magnitude estimation, including magnitudes based on long-period displacement, integrated displacement, and multiband amplitude distribution. We tested the methods using synthetic waveforms calculated from finite fault models of tsunami earthquakes. We found that methods based on observed amplitudes could not estimate magnitude properly, but the method based on the multiband amplitude distribution gave values close to the moment magnitude for many tsunami earthquakes. In this method, peak amplitudes of bandpass filtered waveforms are compared with those of synthetic records for an assumed source duration and fault mechanism. We applied the multiband amplitude distribution method to the records of events that occurred around the Japanese Islands and to those of tsunami earthquakes, and confirmed that this method could be used to estimate event magnitudes close to the moment magnitudes.

Damping and Inertia Coefficients for a Rolling or Swaying Vertical Strip

1963 ◽  
Vol 7 (04) ◽  
pp. 19-23
Author(s):  
J. Kotik
Keyword(s):  
Wave Amplitude ◽  
Added Mass ◽  
Frequency Range ◽  
Entire Frequency Range ◽  
Vertical Strip ◽  
Amplitude Coefficient

Ursell's exact expression3 for the wave-amplitude coefficient for a swaying or rolling vertical strip is evaluated numerically over the entire frequency range. The added-mass and inertia coefficients are then obtained numerically, also over the entire frequency range, via the Kramers-Kronig relations.

Focal mechanism and source depth of earthquakes from body- and surface-wave data

1971 ◽  
Vol 61 (5) ◽  
pp. 1369-1379 ◽  
Author(s):  
Nezihi Canitez ◽  
M. Nafi Toksöz
Keyword(s):  
Surface Wave ◽  
Body Wave ◽  
Source Parameters ◽  
Focal Depth ◽  
Spectral Ratio ◽  
The Body ◽  
Spectral Ratios ◽  
Motion Data ◽  
Wave Data ◽  
Surface Wave Data

abstract The determination of focal depth and other source parameters by the use of first-motion data and surface-wave spectra is investigated. It is shown that the spectral ratio of Love to Rayleigh waves (L/R) is sensitive to all source parameters. The azimuthal variation of the L/R spectral ratios can be used to check the fault-plane solution as well as for focal depth determinations. Medium response, attenuation, and source finiteness seriously affect the absolute spectra and introduce uncertainty into the focal depth determinations. These effects are nearly canceled out when L/R amplitude ratios are used. Thus, the preferred procedure for source mechanism studies of shallow earthquakes is to use jointly the body-wave data, absolute spectra of surface waves, and the Love/Rayleigh spectral ratios. With this procedure, focal depths can be determined to an accuracy of a few kilometers.

Material Parameter Determination in Glass Wool Mat for Sound Absorption

2011 ◽  
Vol 148-149 ◽  
pp. 1271-1275 ◽  
Author(s):  
Cheng Dong Li ◽  
Zhao Feng Chen ◽  
Jie Ming Zhou ◽  
Bin Bin Li ◽  
Wang Ping Wu ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Prediction Error ◽  
Fiber Length ◽  
Normal Incidence ◽  
Glass Wool ◽  
Parameter Determination ◽  
Frequency Range ◽  
Material Parameters ◽  
Refrigeration Equipment ◽  
Building Engineering

Glass wool mat is widely used in the fields of building engineering, transport facilities and refrigeration equipment. In this paper, the effect of material parameters such as density, thickness, porosity, and flow resistivity on the normal incidence absorption coefficient has been studied. In addition, fiber length is also investigated to achieve appropriate strength. The prediction error of normal incidence absorption coefficient by modified Johnson–Allard model is less than 5% in the frequency range between 800 Hz and 5 kHz. We could use the modified Johnson–Allard model to determine the parameter of glass wool mat for better development.

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