THE SEISMIC WAVE SYSTEM FROM A SURFACE IMPACT

Geophysics ◽  
1976 ◽  
Vol 41 (2) ◽  
pp. 243-265 ◽  
Author(s):  
Harold M. Mooney
Keyword(s):  
Rayleigh Waves ◽  
Pulse Length ◽  
Wave System ◽  
P Waves ◽  
S Waves ◽  
Impact Surface ◽  
Seismic Waveforms ◽  
Detector Distance ◽  
Weight Drop ◽  
Drop Impacts

A theory presented in an earlier paper (Mooney, 1974) has been used to compute seismic waveforms produced by a surface impact. Surface detectors are assumed which measure displacement, velocity, acceleration, or strain in either vertical or horizontal components. A physically plausible source waveform is considered which is unidirectional, symmetrical about a peak, and with zero slopes at beginning and end. Theoretical waveforms are presented for models simulating projectile, hammer, and weight‐drop impacts onto granite, concrete, and soil. The waveforms show small but clear P arrivals, large Rayleigh pulses, and no recognizable S waves. P waves are larger on the horizontal sensors, Rayleigh on the vertical. The waveforms differ markedly from one detector type to another and show little resemblance to the source waveform. Distinctive pulse length and amplitude pulse paramaters are selected. Pulse lenths are shown to be relatively insensitive to detector distance, hence conversion factors can be obtained from which to infer source pulse length. These factors were applied to accelerometer waveforms obtained experimentally from steel pellet impacts onto granite, yielding a source pulse length of 30 μsec. This value was used to compute theoretical waveforms which show satisfactory agreement with the experimental waveforms. The measured amplitude parameters are shown to depend upon detector distance r and source pulse length T and amplitude H as [Formula: see text]where n = 1, 1/2 for P and Rayleigh waves, respectively; p = 0, 1/2 for P and Rayleigh waves; and m = 0,1,2,1 for detectors which measure displacement, particle velocity, acceleration, and horizontal strain. An increase in Poisson’s ratio v for the medium produces increased time separation between P and Rayleigh arrivals, and increase in P pulse length and amplitude, no changes in Rayleigh pulse length, and a decrease in Rayleigh amplitude as [Formula: see text].

4. Seismic waves

2018 ◽  
pp. 53-61
Author(s):  
Mike Goldsmith
Keyword(s):  
Seismic Wave ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Shear Waves ◽  
Free Vibrations ◽  
Love Waves ◽  
Sound Waves ◽  
P Waves ◽  
Tectonic Plates ◽  
S Waves

Sound waves travel very easily underground, often for many thousands of kilometres. These are usually referred to as a kind of seismic wave and are most often triggered by earthquakes, which result from a sudden slip of tectonic plates, down to about 700 kilometres below the Earth’s surface. ‘Seismic waves’ describes the four types of seismic wave generated by earthquakes: P-waves (primary waves), S-waves (shear waves), Love waves (usually the most powerful and destructive of seismic waves), and Rayleigh waves, which are created when P and S waves reach the Earth’s surface together, combining to form undulating ground rolls. Free vibrations and star waves are also described.

Numerical simulation of azimuthal acoustic logging in a borehole penetrating a rock formation boundary

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. D283-D291 ◽  
Author(s):  
Peng Liu ◽  
Wenxiao Qiao ◽  
Xiaohua Che ◽  
Xiaodong Ju ◽  
Junqiang Lu ◽  
...  
Keyword(s):  
Domain Model ◽  
P Wave ◽  
S Wave ◽  
Angle Variation ◽  
P Waves ◽  
Acoustic Logging ◽  
S Waves ◽  
Rock Formation ◽  
Logging Tool ◽  
Difference Time

We have developed a new 3D acoustic logging tool (3DAC). To examine the azimuthal resolution of 3DAC, we have evaluated a 3D finite-difference time-domain model to simulate a case in which the borehole penetrated a rock formation boundary when the tool worked at the azimuthal-transmitting-azimuthal-receiving mode. The results indicated that there were two types of P-waves with different slowness in waveforms: the P-wave of the harder rock (P1) and the P-wave of the softer rock (P2). The P1-wave can be observed in each azimuthal receiver, but the P2-wave appears only in the azimuthal receivers toward the softer rock. When these two types of rock are both fast formations, two types of S-waves also exist, and they have better azimuthal sensitivity compared with P-waves. The S-wave of the harder rock (S1) appears only in receivers toward the harder rock, and the S-wave of the softer rock (S2) appears only in receivers toward the softer rock. A model was simulated in which the boundary between shale and sand penetrated the borehole but not the borehole axis. The P-wave of shale and the S-wave of sand are azimuthally sensitive to the azimuth angle variation of two formations. In addition, waveforms obtained from 3DAC working at the monopole-transmitting-azimuthal-receiving mode indicate that the corresponding P-waves and S-waves are azimuthally sensitive, too. Finally, we have developed a field example of 3DAC to support our simulation results: The azimuthal variation of the P-wave slowness was observed and can thus be used to reflect the azimuthal heterogeneity of formations.

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.

An analytical solution to separate P‐waves and S‐waves in VSP wavefields

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 955-967 ◽  
Author(s):  
Hiroshi Amano
Keyword(s):  
Analytical Solution ◽  
Formal Solution ◽  
Seismic Profile ◽  
Synthetic Seismograms ◽  
Third Order ◽  
P Waves ◽  
Practical Applications ◽  
S Waves ◽  
The Third ◽  
Z Domain

An analytical solution to separate P‐waves and S‐waves in vertical seismic profile (VSP) wavefields is derived using combinations of certain terms of the formal solution for forward VSP modeling. Some practical applications of this method to synthetic seismograms and field data are investigated and evaluated. Little wave distortion is recognized, and the weak wavefield masked by dominant wavetrains can be extracted with this method. The decomposed wavefield is expressed in the frequency‐depth (f-z) domain as a linear combination of up to the third‐order differential of traces, which is approximated by trace differences in the practical separation process. In general, five traces with single‐component data are required in this process, but the same process is implemented with only three traces in the acoustic case. Two‐trace extrapolation is applied to each edge of the data gather to enhance the accuracy of trace difference. Since the formulas are developed in the f-z domain, the influence of anelasticity can be taken into account, and the calculation is carried out fast enough with the benefit of the fast Fourier transform (FFT).

scholarly journals Explicit Q expressions for inhomogeneous P- and SV-waves in isotropic viscoelastic media

2019 ◽  
Vol 17 (2) ◽  
pp. 300-312 ◽  
Author(s):  
Xu Liu ◽  
Stewart Greenhalgh ◽  
Bing Zhou ◽  
Huijian Li
Keyword(s):  
Energy Density ◽  
Dissipation Factor ◽  
Energy Balance Equation ◽  
Dissipated Energy ◽  
P Waves ◽  
S Waves ◽  
Viscoelastic Media ◽  
Inhomogeneous Waves ◽  
Inhomogeneity Parameter ◽  
P And Sv Waves

Abstract We derive explicit expressions for the dissipation factors of inhomogeneous P and SV-waves in isotropic viscoelastic media. The Q−1 values are given as concise and simple functions of material parameters and the wave inhomogeneity parameter using two different definitions. Unlike homogenous waves, inhomogeneous waves may have significant differences in the values of dissipation factors because of different definitions. For example, under one of the three dissipation factor definitions that Q−1 is equal to the time-averaged dissipated-energy density divided by twice the time-averaged strain-energy density, it is found and proved that the dissipation factor of SV-waves is totally independent of the inhomogeneity parameter. For materials in which P-waves are normally more dissipative than S-waves (e.g. a porous reservoir), the dissipation factors of P-waves tend to decrease with increasing degree of inhomogeneity. Based on Buchan's classic real value energy balance equation, a parallel investigation is conducted for each step similar to that based on the Carcione equations, including derivation of explicit formulas (with inhomogeneity angle representing the degree of inhomogeneity of a plane wave), and dissipation curves calculations. We also obtain an inhomogeneity independent formula of $Q_{\, SV}^{ - 1}$, and exactly the same phase velocity and attenuation dispersion results for the example material.

Shallow near-surface effects

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. T221-T231 ◽  
Author(s):  
Christine E. Krohn ◽  
Thomas J. Murray
Keyword(s):  
Time Delay ◽  
Velocity Gradient ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
P Waves ◽  
Large Computer ◽  
Near Surface ◽  
S Waves ◽  
High Attenuation ◽  
Pulse Broadening

The top 6 m of the near surface has a surprisingly large effect on the behavior of P- and S-waves. For unconsolidated sediments, the P-wave velocity gradient and attenuation can be quite large. Computer modeling should include these properties to accurately reproduce seismic effects of the near surface. We have used reverse VSP data and computer simulations to demonstrate the following effects for upgoing P-waves. Near the surface, we have observed a large time delay, indicating low velocity ([Formula: see text]), and considerable pulse broadening, indicating high attenuation ([Formula: see text]). Consequently, shallowly buried geophones have greater high-frequency bandwidth compared with surface geophones. In addition, there is a large velocity gradient in the shallow near surface (factor of 10 in 5 m), resulting in the rotation of P-waves to the vertical with progressively smaller amplitudes recorded on horizontal phones. Finally, we have found little indication of a reflection or ghost from the surface, although downgoing reflections have been observed from interfaces within the near surface. In comparison, the following have been observed for upgoing S-waves: There is a small increase in the time delay or pulse broadening near the surface, indicating a smaller velocity gradient and less change in attenuation. In addition, the surface reflection coefficient is nearly one with a prominent surface ghost.

Australian national ocean bottom seismograph fleet advances conventional exploration

2017 ◽  
Vol 57 (2) ◽  
pp. 738
Author(s):  
Alexey Goncharov ◽  
Michal Malinowski ◽  
Dejan Sekulic ◽  
Ashby Cooper ◽  
Peter Chia ◽  
...  
Keyword(s):  
Regional Scale ◽  
Seismic Survey ◽  
Ocean Bottom ◽  
P Waves ◽  
Crust And Upper Mantle ◽  
Seismic Surveys ◽  
S Waves ◽  
Industry Standard ◽  
Ocean Bottom Seismographs ◽  
Obs Data

A fleet of new Australian ocean bottom seismographs (OBSs) have broadband frequency range, and similar instruments are available at only five or six institutions globally. These OBSs are multi-purpose devices able to record passive-source seismic data (earthquakes, ambient noise) as well as active-source (airgun generated) data and, at the same time, to monitor seismic survey noise and whale calls for environmentally responsible exploration. OBS data collected during commercial seismic surveys in Australian waters prove that it is possible to image the velocity distribution of the whole crust and upper mantle from analysis of both reflected and refracted phases generated by an industry-standard broadband airgun array. This means that valuable information on a regional scale can be obtained as a by-product of commercial seismic surveys. Three-component recording capability of OBSs allows analysis of S-waves in addition to the P-waves that are conventionally used in marine reflection surveys.

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