scholarly journals Identification of subsonic P‐waves

Geophysics ◽  
2002 ◽  
Vol 67 (3) ◽  
pp. 909-920 ◽  
Author(s):  
Paul Michaels
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
Rayleigh Waves ◽  
Field Trial ◽  
Water Saturation ◽  
Near Field ◽  
Plasticity Index ◽  
P Waves ◽  
Sandy Silt

A field trial was conducted to test the existence of subsonic (Vp < 331 m/s) P‐waves previously reported in the literature. A 1‐m‐long reverse profile was acquired with three‐component (3C) geophones on a sandy silt (unified classification ML). The silt had a porosity of 54%, a degree of water saturation of 63%, and a plasticity index of 10. No subsonic P‐waves were observed, although high‐frequency (up to 1200 Hz) Rayleigh waves were identified by hodogram analysis. These surface waves were observed with horizontal velocities that varied from 40 to 200 m/s. Hodogram observations and theory suggest that a portion of the data were also in the near‐field.

SIGNAL AND NOISE IN DEEP WELLS

Geophysics ◽  
1964 ◽  
Vol 29 (5) ◽  
pp. 721-732 ◽  
Author(s):  
Eduard J. Douze
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
Rayleigh Waves ◽  
Frequency Noise ◽  
Low Velocity ◽  
P Waves ◽  
High Frequency Noise ◽  
Deep Well ◽  
Velocity Wave ◽  
Deep Wells

Deep‐well measurements at Grapevine, Texas; Hobart, Oklahoma; and Orlando, Florida, show that the noise is composed of surface waves that decrease in amplitude with depth. At Hobart, a low‐velocity wave guide contains wave‐guided noise. Fundamental and higher mode Rayleigh waves appear to be present in the noise at each site. The amplitudes of incident P waves depend on the depth at which the deep‐well seismometer is operated. High‐frequency P waves from quarry blasts are clearly visible in recordings from the deep‐well seismometer because the high‐frequency noise is suppressed at depth.

Simultaneous body and surface wave retrieval from the seismic ambient field and discrimination from unavoidably arising spurious artifacts

2020 ◽  
Author(s):  
Ali Riahi ◽  
Zaher-Hossein Shomali ◽  
Anne Obermann ◽  
Ahmad Kamayestani
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Ambient Noise ◽  
Low Frequency ◽  
The Body ◽  
Body Waves ◽  
Apparent Velocity ◽  
Noise Sources ◽  
P Waves ◽  
Seismic Ambient Noise

&lt;p&gt;We simultaneously extract both, direct P-waves and Rayleigh waves, from the seismic ambient noise field recorded by a dense seismic network in Iran. With synthetics, we show that the simultaneous retrieval of body and surface waves from seismic ambient noise leads to the unavoidable appearance of spurious arrivals that could lead to misinterpretations.&lt;/p&gt;&lt;p&gt;We work with 2 months of seismic ambient noise records from a dense deployment of 119 sensors with interstation distances of 2 km in Iran. To retrieve body and surface waves, we calculate the cross-coherency in low-frequency ranges, i.e. frequencies up to 1.2 Hz, to provide the empirical Green&amp;#8217;s functions between each pair of stations. To separate the P and Rayleigh waves, we use the polarization method that also enhances the small amplitude body waves.&lt;/p&gt;&lt;p&gt;We observe both P and Rayleigh waves with an apparent velocity of 4.9&amp;#177;0.3 and 1.8&amp;#177;0.1 km/s in the studied area, respectively, as well as S or higher mode of Rayleigh waves, with an apparent velocity of 4.1&amp;#177;0.1 km/s. Besides these physical arrivals, we also observe two spurious arrivals with similar amplitudes before/after the P and/or Rayleigh waves that render the discrimination challenging.&lt;/p&gt;&lt;p&gt;To better understanding these arrivals, we perform synthetic tests. We show that simultaneously retrieving the body and surface waves from seismic ambient noise sources will unavoidably lead to the appearance of superior arrivals in the calculation of empirical Green&amp;#8217;s functions.&lt;/p&gt;

Weakly nonlinear surface waves in magnetohydrodynamics. I

2020 ◽  
pp. 1-35
Author(s):  
Olivier Pierre ◽  
Jean-François Coulombel
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
Rayleigh Waves ◽  
Three Dimensional ◽  
Type Equation ◽  
Approximate Solutions ◽  
Vortex Sheet ◽  
Solvability Conditions ◽  
Weakly Nonlinear ◽  
High Frequency Oscillations

This work is devoted to the construction of weakly nonlinear, highly oscillating, current vortex sheet solutions to the system of ideal incompressible magnetohydrodynamics. Current vortex sheets are piecewise smooth solutions that satisfy suitable jump conditions on the (free) discontinuity surface. In this article, we complete an earlier work by Alì and Hunter (Quart. Appl. Math. 61(3) (2003) 451–474) and construct approximate solutions at any arbitrarily large order of accuracy to the three-dimensional free boundary problem when the initial discontinuity displays high frequency oscillations. As evidenced in earlier works, high frequency oscillations of the current vortex sheet give rise to ‘surface waves’ on either side of the sheet. Such waves decay exponentially in the normal direction to the current vortex sheet and, in the weakly nonlinear regime which we consider here, their leading amplitude is governed by a nonlocal Hamilton–Jacobi type equation known as the ‘HIZ equation’ (standing for Hamilton–Il’insky–Zabolotskaya (J. Acoust. Soc. Amer. 97(2) (1995) 891–897)) in the context of Rayleigh waves in elastodynamics. The main achievement of our work is to develop a systematic approach for constructing arbitrarily many correctors to the leading amplitude. We exhibit necessary and sufficient solvability conditions for the corrector equations that need to be solved iteratively. The verification of these solvability conditions is based on mere algebra and arguments of combinatorial analysis, namely a Leibniz type formula which we have not been able to find in the literature. The construction of arbitrarily many correctors enables us to produce infinitely accurate approximate solutions to the current vortex sheet equations. Eventually, we show that the rectification phenomenon exhibited by Marcou in the context of Rayleigh waves (C. R. Math. Acad. Sci. Paris 349(23–24) (2011) 1239–1244) does not arise in the same way for the current vortex sheet problem.

scholarly journals Toggling Near‐Field Directionality via Polarization Control of Surface Waves

2021 ◽  
Vol 15 (4) ◽  
pp. 2000388
Author(s):  
Yuhan Zhong ◽  
Xiao Lin ◽  
Jing Jiang ◽  
Yi Yang ◽  
Gui‐Geng Liu ◽  
...  
Keyword(s):  
Surface Waves ◽  
Near Field ◽  
Polarization Control

scholarly journals The appearance of boundary layers and drift flows due to high-frequency surface waves

2012 ◽  
Vol 707 ◽  
pp. 482-495 ◽  
Author(s):  
Ofer Manor ◽  
Leslie Y. Yeo ◽  
James R. Friend
Keyword(s):  
Boundary Layer ◽  
Surface Waves ◽  
High Frequency ◽  
Slip Boundary Condition ◽  
Inertial Effects ◽  
Velocity Amplitude ◽  
Slip Boundary ◽  
Long Period ◽  
Bulk Waves ◽  
Schlichting Streaming

AbstractThe classical Schlichting boundary layer theory is extended to account for the excitation of generalized surface waves in the frequency and velocity amplitude range commonly used in microfluidic applications, including Rayleigh and Sezawa surface waves and Lamb, flexural and surface-skimming bulk waves. These waves possess longitudinal and transverse displacements of similar magnitude along the boundary, often spatiotemporally out of phase, giving rise to a periodic flow shown to consist of a superposition of classical Schlichting streaming and uniaxial flow that have no net influence on the flow over a long period of time. Correcting the velocity field for weak but significant inertial effects results in a non-vanishing steady component, a drift flow, itself sensitive to both the amplitude and phase (prograde or retrograde) of the surface acoustic wave propagating along the boundary. We validate the proposed theory with experimental observations of colloidal pattern assembly in microchannels filled with dilute particle suspensions to show the complexity of the boundary layer, and suggest an asymptotic slip boundary condition for bulk flow in microfluidic applications that are actuated by surface waves.

scholarly journals Measurement of high frequency conductivity of oxide-doped anti-ferromagnetic thin film with a near-field scanning microwave microscope

AIP Advances ◽  
2014 ◽  
Vol 4 (4) ◽  
pp. 047114 ◽  
Author(s):  
Z. Wu ◽  
A. D. Souza ◽  
B. Peng ◽  
W. Q. Sun ◽  
S. Y. Xu ◽  
...  
Keyword(s):  
Thin Film ◽  
High Frequency ◽  
Near Field ◽  
Microwave Microscope ◽  
Near Field Scanning

Application Of Elastic Layers To Register Pressure Field On The Model Surface In Supersonic Flow

2016 ◽  
Vol 11 (1) ◽  
pp. 23-33
Author(s):  
Maxim Golubev ◽  
Andrey Shmakov
Keyword(s):  
Surface Waves ◽  
High Frequency ◽  
High Speed ◽  
Pressure Pulsation ◽  
Pressure Field ◽  
Leading Edge ◽  
Supersonic Wind Tunnel ◽  
Register Pressure ◽  
Elastic Layers ◽  
Sharp Leading Edge

The work presents the results of application of panoramic interferential technique which is based on elastic layers (sensors) usage to obtain pressure distribution on the flat plate having sharp leading edge. Experiments were done in supersonic wind tunnel at Mach number M = 4. Sensitivity and response time are shown to be enough to register pressure pulsation against standing and traveling sensor surface waves. Applying high-frequency image acquiring is demonstrated to make possible to distinguish at visualization images high-speed disturbances propagating in the boundary layer from low-speed surface waves

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