Seismic radiation from a point source on the surface of a cylindrical cavity

Geophysics ◽  
1978 ◽  
Vol 43 (6) ◽  
pp. 1071-1082 ◽  
Author(s):  
Roy J. Greenfield
Keyword(s):  
Cylindrical Cavity ◽  
High Frequency ◽  
Seismic Source ◽  
P Wave ◽  
Point Force ◽  
Shielding Effect ◽  
S Wave ◽  
Source Data ◽  
Mine Roof ◽  
Direction Opposite

The presence of a void or cavity in the vicinity of a seismic source will modify the radiated signal from the classic solution for a point force in an infinite medium. To study this effect, solutions were obtained for the seismic fields from a point force applied to the surface of a cylindrical cavity in an elastic medium. The solutions were evaluated to give P‐ and S‐wave frequency domain radiation patterns. For P wavelengths less than about 3 times the cavity diameter, the cavity acts to decrease the P‐wave amplitude going outward in the direction opposite the source. Data taken in two coal mines show this shielding effect. High‐frequency energy was observed, with surface seismometers, for signals generated by hitting the mine roof, whereas the high‐frequency energy was much smaller on signals generated by hitting the floor. Time domain calculations show that the P‐wave signal is delayed by approximately the time it takes an S‐wave to propagate around the cylinder.

Shallow to very shallow, high‐resolution reflection seismic using a portable vibrator system

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1295-1309 ◽  
Author(s):  
Ranajit Ghose ◽  
Vincent Nijhof ◽  
Jan Brouwer ◽  
Yoshikazu Matsubara ◽  
Yasuhiro Kaida ◽  
...  
Keyword(s):  
High Resolution ◽  
High Frequency ◽  
Seismic Waves ◽  
Soft Soil ◽  
Geophysical Methods ◽  
Seismic Source ◽  
P Wave ◽  
Nondestructive Technique ◽  
Buried Objects ◽  
Reflection Seismic

In shallow engineering‐geophysical applications, there is a lack of controlled, nondestructive, high‐resolution mapping tools, particularly for the target depth that ground‐penetrating radar cannot reach but which is too shallow for other conventional geophysical methods. For soft soil, this corresponds to a depth of 2 to 30 m. We have developed a portable, high‐frequency P-wave vibrator system that is capable of bridging this gap. As far as the important contribution of the seismic source is concerned, penetration and resolution can be individually controlled through easy modulation of the sweep signal generated by this electromagnetic vibrator. The feasibility of this system has been tested in shallow (10–50 m) to very shallow (0–10 m) applications. Seven field data sets representing varying geology, site conditions, and exploration targets are presented to illustrate the applicability. The first three examples show the potential of this portable vibrator source in shallow applications. Under favorable situations, a maximum resolution of about 20 cm for events located at 15–30 m depth could be achieved. Because high‐frequency seismic waves suffer from severe attenuation in the dry, unsaturated weathered zone, the penetration is relatively limited when the water table is deeper than 4–5 m. The fourth to seventh field examples illustrate very shallow applications at noisy, asphalt‐paved urban sites that are often encountered in civil, geotechnical, and environmental engineering projects. The prospecting targets were thin soil layers or small buried objects. On asphalt, the vibrator can produce high‐frequency energy easily. The fourth example shows high‐resolution delineation of very shallow soil structures. The last three examples present successful location of buried bodies—often small and closely spaced—in soft soil at depths of 0.5 to 5 m. We observe well‐defined reflection events of frequency exceeding 200 Hz. These results suggest that high‐frequency seismic reflection imaging using the portable vibrator system can indeed serve as a powerful, nondestructive technique for shallow to very shallow underground prospecting.

Orbital vibrator seismic source for simultaneous P‐ and S‐wave crosswell acquisition

Geophysics ◽  
2001 ◽  
Vol 66 (5) ◽  
pp. 1471-1480 ◽  
Author(s):  
Thomas M. Daley ◽  
Dale Cox
Keyword(s):  
Seismic Energy ◽  
Seismic Source ◽  
P Wave ◽  
S Wave ◽  
Circularly Polarized ◽  
S Waves ◽  
Polarized Waves ◽  
Coordinate Rotation ◽  
Processing Algorithms ◽  
Borehole Seismic

A recently developed borehole seismic source, the orbital vibrator, was successfully deployed in a crosswell survey in a fractured basalt aquifer. This seismic source uses a rotating eccentric mass to generate seismic energy. Source sweeps with clockwise and counter‐clockwise rotations are recorded at each source location. Because this source generates circularly polarized waves, unique processing algorithms are used to decompose the recordings into two equivalent linearly oscillating, orthogonally oriented seismic sources. The orbital vibrator therefore generates P‐ and S‐waves simultaneously for all azimuths. A coordinate rotation based on P‐wave particle motion is used to align the source components from various depths. In a field experiment, both P‐ and S‐wave arrivals were recorded using fluid‐coupled hydrophone sensors. The processed field data show clear separation of P‐ and S‐wave arrivals for in‐line and crossline source components, respectively. A tensor convolutional description of the decomposition process allows for extension to multicomponent sensors.

The effects of near-source heterogeneity on shear-wave evolution

Geophysics ◽  
2014 ◽  
Vol 79 (4) ◽  
pp. T233-T241 ◽  
Author(s):  
Christopher S. Sherman ◽  
James Rector ◽  
Steven Glaser
Keyword(s):  
Wave Propagation ◽  
Wave Energy ◽  
Mode Conversion ◽  
Near Field ◽  
Seismic Source ◽  
Elastic Half Space ◽  
P Wave ◽  
S Wave ◽  
Rytov Approximation ◽  
Model Features

The Born and Rytov approximation, radiative transfer theory, and other related techniques are commonly used to model features of wave propagation through heterogeneous geologic media such as scattering, attenuation, and pulse-broadening. However, due to the underlying assumptions about the scattering direction and the reference Green’s function, these methods overlook important features of the wavefield such as mode conversion and near-field term coupling. These effects are particularly important within the predicted S-wave nodes of a seismic source, so we analyzed the problem of wave propagation beneath a vertical-point force on the surface of a heterogeneous, elastic half space. To do this, we generated a suite of 3D synthetic heterogeneous geologic models using fractal statistics and simulated the wave propagation using the finite-difference method. We derived an estimate for the effective source radiation patterns, and we used these to compare the results of the models. Our numerical results showed that, due to a combination of mode conversion and near-source coupling effects, S-wave energy on the order of 10% of the P-wave energy is generated within the shear-radiation node. In some cases, this S-wave energy may occur as a coherent pulse and may be used to enhance seismic imaging.

Relation between P- and S-wave corner frequencies in the seismic spectrum

1974 ◽  
Vol 64 (6) ◽  
pp. 1621-1627 ◽  
Author(s):  
J. C. Savage
Keyword(s):  
High Frequency ◽  
Body Wave ◽  
Fault Model ◽  
P Wave ◽  
Corner Frequency ◽  
Rupture Propagation ◽  
S Wave ◽  
P Waves ◽  
Fault Surface ◽  
S Waves

abstract A comprehensive set of body-wave spectra has been calculated for the Haskell fault model generalized to a circular fault surface. These spectra are used to show that in practice the P-wave corner frequency (ƒp) may exceed the S-wave corner frequency (ƒs) when near-sonic or transonic rupture propagation obtains. The explanation appears to be that in such cases ƒs is so large that it is not identified within the recorded band, but rather a secondary corner is mistaken for ƒs. As a consequence of failing to detect the true asymptotic trend, the high-frequency falloff of the spectrum with frequency is substantially less for S waves than for P waves. This explanation appears to be consistent with the demonstration by Molnar, Tucker, and Brune (1973) that ƒp may exceed ƒs.

scholarly journals A novel method for determining the small-strain shear modulus of soil using the bender elements technique

2017 ◽  
Vol 54 (2) ◽  
pp. 280-289 ◽  
Author(s):  
Yejiao Wang ◽  
Nadia Benahmed ◽  
Yu-Jun Cui ◽  
Anh Minh Tang
Keyword(s):  
Shear Modulus ◽  
Shear Wave ◽  
Shear Wave Velocity ◽  
High Frequency ◽  
Small Strain ◽  
P Wave ◽  
S Wave ◽  
Bender Elements ◽  
Small Strain Shear Modulus ◽  
First Arrival

Bender elements technique has become a popular tool for determining shear wave velocity, Vs, hence the small-strain shear modulus of soils, Gmax, thanks to its simplicity and nondestructive character among other advantages. Several methods were proposed to determine the first arrival of Vs. However, none of them can be widely adopted as a standard and there is still an uncertainty on the detection of the first arrival. In this study, bender elements tests were performed on lime-treated soil and both shear wave and compression wave velocities at various frequencies were measured. In-depth analysis showed that the S-wave received signal presents an identical travel time and opposite polarity compared with that of the S-wave components in P-wave received signal, especially at high frequency. From this observation, a novel interpretation method based on the comparison between the S-wave and P-wave received signals at high frequency is proposed. This method enables the determination of the arrival time of the S-wave objectively, avoiding a less reliable first arrival pick-up point. Furthermore, the “π-point” method and cross-correlation method were also employed and the obtained results agree well with those from the proposed method, indicating the accuracy and reliability of the latter. The effects of frequency on the shear wave velocity are also discussed.

Three-component seismic land streamer study of an esker architecture through S- and surface-wave imaging

Geophysics ◽  
2018 ◽  
Vol 83 (6) ◽  
pp. B339-B353 ◽  
Author(s):  
Bojan Brodic ◽  
Alireza Malehmir ◽  
André Pugin ◽  
Georgiana Maries
Keyword(s):  
Surface Wave ◽  
Seismic Source ◽  
Transverse Component ◽  
P Wave ◽  
Wave Component ◽  
Sh Wave ◽  
S Wave ◽  
Near Surface ◽  
Wave Velocities ◽  
Wave Nature

We deployed a newly developed 3C microelectromechanical system-based seismic land streamer over porous glacial sediments to delineate water table and bedrock in Southwestern Finland. The seismic source used was a 500 kg vertical impact drop hammer. We analyzed the SH-wave component and interpreted it together with previously analyzed P-wave component data. In addition to this, we examined the land streamer’s potential for multichannel analysis of surface waves and delineated the site’s stratigraphy with surface-wave-derived S-wave velocities and [Formula: see text] ratios along the entire profile. These S-wave velocities and [Formula: see text] ratios complement the interpretation conducted previously on P-wave stacked section. Peculiarly, although the seismic source used is of a vertical-type nature, the data inspection indicated clear bedrock reflection on the horizontal components, particularly the transverse component. This observation led us to scrutinize the horizontal component data through side-by-side inspection of the shot records of all the three components and particle motion analysis to confirm the S-wave nature of the reflection. Using the apparent moveout velocity of the reflection, as well as the known depth to bedrock based on drilling, we used finite-difference synthetic modeling to further verify its nature. Compared with the P-wave seismic section, bedrock is relatively well delineated on the transverse component S-wave section. Some structures connected to the kettle holes and other stratigraphic units imaged on the P-wave results were also notable on the S-wave section, and particularly on the surface-wave derived S-wave velocity model and [Formula: see text] ratios. Our results indicate that P-, SV-, and SH-wave energy is generated simultaneously at the source location itself. This study demonstrates the potential of 3C seismic for characterization and delineation of the near-surface seismics.

Seismic source spectrum of microearthquakes

1992 ◽  
Vol 82 (6) ◽  
pp. 2391-2409
Author(s):  
Yoshihisa Iio
Keyword(s):  
Wave Velocity ◽  
High Frequency ◽  
Hard Rock ◽  
Ground Surface ◽  
Seismic Source ◽  
P Wave ◽  
Source Spectrum ◽  
Anelastic Attenuation ◽  
P Wave Velocity ◽  
Source Spectra

Abstract The seismic source spectra of microearthquakes having seismic moments between 1014 and 1018 dyne cm were investigated by using local recordings from an excellent hard-rock site. The P-wave velocity near the site was estimated as about 6 km/sec, even immediately below the ground surface. The effect of anelastic attenuation was thought to be very small, since predominant frequencies of greater than 100 Hz were detected in seismograms recorded at focal distances greater 10 km. Many seismograms with S-P times of less than 0.6 sec were observed. The first cycle of the P-wave velocity seismogram was used in this study. The waveforms after the first cycle are likely formed near the site, since their periods are exactly the same for earthquakes that have different source processes. In the high-frequency portion of the estimated displacement source spectra, the slopes of the fall-off have values much greater than 2. The source process of microearthquakes is assumed to be very slow and smooth.

Krauklis wave initiation in fluid-filled fractures by seismic body waves

Geophysics ◽  
2014 ◽  
Vol 79 (1) ◽  
pp. T27-T35 ◽  
Author(s):  
Marcel Frehner
Keyword(s):  
Large Amplitude ◽  
Incidence Angle ◽  
Seismic Source ◽  
Body Waves ◽  
P Wave ◽  
Seismic Exploration ◽  
Fractured Reservoir ◽  
S Wave ◽  
Fracture Orientation ◽  
Seismic Body Waves

Krauklis waves are a special wave mode that is bound to and propagates along fluid-filled fractures. They can repeatedly propagate back and forth along a fracture and eventually fall into resonance emitting a seismic signal with a dominant characteristic frequency. They are of great interest because this resonant behavior can lead to strongly frequency-dependent propagation effects for seismic body waves and may explain seismic tremor generation in volcanic areas or affect microseismic signals in fractured fluid reservoirs. It has been demonstrated that Krauklis waves can be initiated by a seismic source inside the fracture, for example by hydrofracturing. Here, the aim is to study Krauklis wave initiation by an incident plane P- or S-wave in numerical simulations. Both seismic body waves are reflected and scattered at the fracture, but also, two Krauklis waves are initiated with significant amplitude, one at each fracture tip (i.e., at the diffraction-points of the fracture). Generally, the incident S-wave initiates larger-amplitude Krauklis waves compared to the incident P-wave case. For both incident wave modes, the initiation of Krauklis waves strongly depends on the fracture orientation. In the case of an incident P-wave, large-amplitude Krauklis waves are initiated at moderate (12°–40°) and high ([Formula: see text]) inclination angles of the fracture with a distinct gap at approximately 50°. The dependency of Krauklis wave initiation on fracture orientation is almost inversed in the case of an incident S-wave and the largest-amplitude Krauklis waves are initiated at an S-wave incidence angle of approximately 50°. The initiation of large-amplitude Krauklis waves by both P- and S-waves has important implications for earthquake signals propagating through fluid-bearing fractured rocks (volcanic areas, fluid-reservoirs) or for seismic exploration surveys in fractured reservoir situations.

scholarly journals SOURCE LOCATION MECHANISM OF MICROSEISMIC MONITORING USING P-S WAVES AND ITS EFFECT ANALYSIS

10.6036/10370 ◽  
2022 ◽  
Vol 97 (1) ◽  
pp. 39-45
Author(s):  
Zhigang Wang ◽  
Ji Li ◽  
Bo Li
Keyword(s):  
Monitoring Network ◽  
Seismic Source ◽  
Microseismic Monitoring ◽  
Source Location ◽  
P Wave ◽  
Monitoring Networks ◽  
Distributed Monitoring ◽  
S Wave ◽  
Location Accuracy ◽  
Seismic Source Location

Seismic source location is the most fundamental and most important problem in microseismic monitoring. However, only P wave has been mostly applied in the existing microseismic monitoring networks, with low location accuracy and poor stability of location result for the microseismic events occurring beyond monitoring networks. The seismic source location was implemented using P wave and S wave in this study to expand the effective monitoring area of a microseismic monitoring network and improve its location accuracy for microseismic events nearby the monitoring network. Then, the seismic source location mechanism using P-S wave was revealed through theoretical derivation and analysis. Subsequently, the program development and numerical simulation were combined to analyze and compare systematically the location effects of differently distributed monitoring networks, those consisting of different quantities of sensors, and those with S wave contained in some sensors under two circumstances: combination of P wave and S wave and single use of P wave. Results demonstrate that adding S wave in the plane enhances the accuracy control in the radius direction of the monitoring network. After S wave is included, the location accuracy within a certain area beyond the monitoring network is improved considerably, the effective monitoring area of the whole network is expanded, and the unstable location zones using only P wave are eliminated. The location results of differently distributed monitoring networks and the influence laws of the quantity of sensors constituting the networks on the location results are acquired. This study provides evidence for microseismic monitoring to realize accurate and stable location within a larger range. Keywords: seismic source location, P wave and S wave, mechanism, location effect

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