Extraction of the surface waves and waveguide modes of the Green's function in layered anisotropic dielectrics between two ground planes

Radio Science ◽  
2002 ◽  
Vol 37 (4) ◽  
pp. 15-1-15-8 ◽  
Author(s):  
Ben Song ◽  
Wei Hong
Keyword(s):  
Green’S Function ◽  
Surface Waves ◽  
Green's Function ◽  
Waveguide Modes ◽  
Anisotropic Dielectrics

The Search of Diffusive Properties in Ambient Seismic Noise

2021 ◽  
Author(s):  
José Piña-Flores ◽  
Martín Cárdenas-Soto ◽  
Antonio García-Jerez ◽  
Michel Campillo ◽  
Francisco J. Sánchez-Sesma
Keyword(s):  
Green’S Function ◽  
Surface Waves ◽  
Green's Function ◽  
Seismic Noise ◽  
Elastic Field ◽  
Spectral Ratio ◽  
Ambient Seismic Noise ◽  
Data Sets ◽  
Original Experiment ◽  
Imaging Theory

ABSTRACT Ambient seismic noise (ASN) is becoming of interest for geophysical exploration and engineering seismology, because it is possible to exploit its potential for imaging. Theory asserts that the Green’s function can be retrieved from correlations within a diffuse field. Surface waves are the most conspicuous part of Green’s function in layered media. Thus, the velocities of surface waves can be obtained from ASN if the wavefield is diffuse. There is widespread interest in the conditions of emergence and properties of diffuse fields. In the applications, useful approximations of the Green’s function can be obtained from cross correlations of recorded motions of ASN. An elastic field is diffuse if the background illumination is azimuthally uniform and equipartitioned. It happens with the coda waves in earthquakes and has been verified in carefully planned experiments. For one of these data sets, the 1999 Chilpancingo (Mexico) experiment, there are some records of earthquake pre-events that undoubtedly are composed of ASN, so that the processing for coda can be tested on them. We decompose the ASN energies and study their equilibration. The scheme is inspired by the original experiment and uses the ASN recorded in an L-shaped array that allows the computation of spatial derivatives. It requires care in establishing the appropriate ranges for measuring parameters. In this search for robust indicators of diffusivity, we are led to establish that under certain circumstances, the S and P energy equilibration is a process that anticipates the diffusion regime (not necessarily isotropy), which justifies the use of horizontal-to-vertical spectral ratio in the context of diffuse-field theory.

Rupture directivity and slip distribution for the Ms 6.8 earthquake of 6 April 1992, Offshore British Columbia: An application of the empirical Green's function method using surface waves

1995 ◽  
Vol 85 (3) ◽  
pp. 736-746
Author(s):  
John F. Cassidy
Keyword(s):  
Green’S Function ◽  
Surface Waves ◽  
Green's Function ◽  
Function Method ◽  
Slip Distribution ◽  
Rupture Directivity ◽  
Aftershock Activity ◽  
Empirical Green’S Function ◽  
Rupture Model ◽  
Empirical Green's Function

Abstract On 6 April 1992 at 13:55 UT, an earthquake of Ms = 6.8 occurred along the Revere-Dellwood-Wilson (RDW) fault, in the triple-junction region at the northern end of the Cascadia subduction zone. This was the first significant event in this region recorded by modern digital broadband seismic networks, thus providing the first opportunity to examine the rupture process of a major earthquake along this young oceanic transform fault. In this article, an empirical Green's Function technique is applied to regional and teleseismic surface waves to estimate the rupture directivity, the extent of rupture, and the slip distribution along the Revere-Dellwood-Wilson fault associated with this earthquake. The 20-sec low-pass-filtered relative source time functions (RSTF's) are single pulses with an azimuthal variation in the pulse width. This suggests that the rupture propagated to the NW (315° ± 20°), along the Revere-Dellwood-Wilson fault (striking 326°). Higher frequency RSTF's reveal two discrete subevents. The clear azimuthal variation in the time separation of these subevents requires that relative to the first subevent, the second is located 13 to 20 km in the direction 345° ± 20°. Using the RSTF at HRV (perpendicular to the rupture direction), a total rupture length of 35 km is estimated, with the bulk of the slip concentrated in a 20-km-long segment of the RDW fault to the northwest of the epicenter. Two peaks are observed in the estimated slip distribution, with maximum values of 1.8 and 1.1 m, respectively. The rupture model derived from this analysis is similar to that obtained from the analysis of body waves and is consistent with the results of aftershock studies. The latter indicate a paucity of aftershock activity (and low moment release) in the 20-km-long segment of the RDW fault to the NW of the epicenter. A distinct peak in aftershock activity 30 to 40 km to the NW of the epicenter likely represents the termination of rupture. The good agreement between the results of this study, the rupture model estimated from body-wave analysis, and the aftershock distribution bode well for the application of the empirical Green's function method using surface waves. It suggests that this method could be applied to large, historic earthquakes in this region, for which regional and teleseismic surface waves are often the most reliable data set.

scholarly journals Modeling P waves in seismic noise correlations: Application to fault monitoring using train traffic sources

2021 ◽  
Author(s):  
Korbinian Sager ◽  
Victor Tsai ◽  
Yixiao Sheng ◽  
Florent Brenguier ◽  
Pierre Boué ◽  
...  
Keyword(s):  
Green’S Function ◽  
Surface Waves ◽  
Green's Function ◽  
Seismic Waves ◽  
Low Frequency ◽  
Body Waves ◽  
Noise Sources ◽  
P Waves ◽  
Promising Alternative ◽  
Fault Monitoring

The theory of Green's function retrieval essentially requires homogeneously distributed noise sources. Even though these conditions are not fulfilled in nature, low-frequency (<1 Hz) surface waves generated by ocean-crust interactions have been used successfully to image the crust with unprecedented spatial resolution. In contrast to low-frequency surface waves, high-frequency (>1 Hz) body waves have a sharper, more localized sensitivity to velocity contrasts and temporal changes at depth. In general, their retrieval using seismic interferometry is challenging, and recent studies focus on powerful, localized noise sources. They have proven to be a promising alternative but break the assumptions of Green's function retrieval. In this study, we present an approach to model correlations between P waves for these scenarios and analyze their sensitivity to 3D Earth structure. We perform a series of numerical experiments to advance our understanding of these signals and prepare for an application to fault monitoring. In the considered cases, the character of the signals strongly diverges from Green's function retrieval, and the sensitivity to structure has significant contributions in the source direction. An accurate description of the underlying physics allows us to reproduce observations made in the context of monitoring the San Jacinto Fault in California using train-generated seismic waves. This approach provides new perspectives for detecting and localizing temporal velocity changes previously unnoticed by commonly exploited surface-wave reconstructions.

Short surface waves in the presence of a finite dock. II

1964 ◽  
Vol 60 (4) ◽  
pp. 985-1012 ◽  
Author(s):  
R. L. Holford
Keyword(s):  
Green’S Function ◽  
Surface Waves ◽  
Green's Function ◽  
High Frequency ◽  
Short Waves ◽  
High Frequency Oscillations

AbstractThe generalized wave-making problem for the forced high-frequency oscillations of a finite dock is solved through use of the Green's function obtained in the first part of this paper. The specific cases of heave and roll are considered with particular reference to the forces on the dock and the amplitude and phase of the radiated waves. These results are then utilized to solve the problem of transmission of short waves under a fixed dock.

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