EFFECT OF SEDIMENTARY THICKNESS ON SHORT‐PERIOD RAYLEIGH‐WAVE DISPERSION

Geophysics ◽  
1965 ◽  
Vol 30 (2) ◽  
pp. 198-203 ◽  
Author(s):  
T. V. McEvilly ◽  
William Stauder
Keyword(s):  
Rayleigh Waves ◽  
Wave Dispersion ◽  
Illinois Basin ◽  
Well Control ◽  
Short Period ◽  
Single Station ◽  
Basement Depth ◽  
Basin Area ◽  
Rayleigh Wave Dispersion ◽  
Group Velocities

Large differences in group velocities of short‐period Rayleigh waves from stripmine blasts for different propagation paths in the Ozark Uplift‐Illinois Basin area have been observed. Good well control in the area makes possible the construction of structural models of the sediments‐basement system for these paths. Theoretical group velocities computed for these models agree well with observations, thus explaining the large variations in velocities in terms of basement‐depth differences. This sensitivity of short‐period surface waves to sedimentary thickness suggests an inexpensive, single‐station technique of basin reconnaissance where commercial blasting is available.

scholarly journals Crustal structure of the Andes from Rayleigh wave dispersion

1961 ◽  
Vol 51 (3) ◽  
pp. 381-388 ◽  
Author(s):  
Armando Cisternas
Keyword(s):  
Rayleigh Waves ◽  
Theoretical Models ◽  
Wave Dispersion ◽  
Pass Filter ◽  
Low Pass Filter ◽  
The Andes ◽  
Short Period ◽  
Low Pass ◽  
Empirical Curve ◽  
Rayleigh Wave Dispersion

Abstract Records from a Benioff short-period seismograph located at Huancayo, Peru, are digitalized and then passed through a low-pass filter to get the long-period waves. In this way the dispersion curves of Rayleigh waves for paths along the Andes can be computed from seismograms which otherwise would be unusable. The comparison with the empirical curve for a “normal” continental crust (Press 1960) and with specially computed theoretical models indicates a crustal thickness of the order of 50 km. For periods between 20 and 25 sec., the observed group velocity shows abnormally low values.

Short-period Rayleigh-wave dispersion across the Tibetan Plateau

1975 ◽  
Vol 65 (5) ◽  
pp. 1051-1057 ◽  
Author(s):  
W. P. Chen ◽  
P. Molnar
Keyword(s):  
Tibetan Plateau ◽  
Simple Wave ◽  
Wave Dispersion ◽  
New Delhi ◽  
The Tibetan Plateau ◽  
Period Range ◽  
Short Period ◽  
Wave Forms ◽  
Wave Trains ◽  
Rayleigh Wave Dispersion

Abstract Well-dispersed Rayleigh waves within the period range of 4 to 11 sec are observed at New Delhi (NDI) and Shillong (SHL), India, for seven earthquakes near and in the Tibetan Plateau from 1963 to 1971. The dispersion curves and the simply dispersed wave forms suggest a prominent overlying wave guide, probably sediments, in the Tibetan area. The thickness of such sediments is most likely between 2.5 and 7.0 km. The simple wave trains, without much distortion due to multipathing, are consistent with a relatively inert, recent tectonism in Tibet.

Surface-wave dispersion computations

1970 ◽  
Vol 60 (2) ◽  
pp. 321-344 ◽  
Author(s):  
Fred Schwab ◽  
Leon Knopoff
Keyword(s):  
Half Space ◽  
Rayleigh Waves ◽  
Wave Dispersion ◽  
Reduction Technique ◽  
Surface Wave Dispersion ◽  
Single Precision ◽  
Homogeneous Half Space ◽  
Full Control ◽  
Significant Figures ◽  
Rayleigh Wave Dispersion

abstract Fundamental-mode Love- and Rayleigh-wave dispersion computations for multilayered, perfectly-elastic media were studied. The speed of these computations was improved, and the accuracy brought under full control. With sixteen decimal digits employed in these computations, fifteen significant-figure accuracy was found possible with Love waves and twelve to thirteen figure accuracy with Rayleigh waves. In order to ensure that the computed dispersion is correct to a specified accuracy, say σ significant figures, (σ + 1)/4 wavelengths of layered structure must be retained above a homogeneous half-space. To this accuracy, the homogeneous half-space is a sufficient model of the true layering it replaces. Using this result, it was possible to refine the usual layer-reduction technique so as to ensure retention of the specified accuracy while employing reduction. With this reduction technique in effect, and with σ specified below single-precision accuracy, the program can be run entirely in single precision; the specified accuracy is maintained without overflow or loss-of-precision problems being encountered during calculations.

scholarly journals Automated detection and association of surface waves

1994 ◽  
Vol 37 (3) ◽  
Author(s):  
R. G. North ◽  
C. R. D. Woodgold
Keyword(s):  
Surface Waves ◽  
Group Velocity ◽  
Rayleigh Waves ◽  
Arrival Time ◽  
Narrow Band ◽  
Broad Band ◽  
Detection Algorithm ◽  
Automated Detection ◽  
Short Period ◽  
Group Velocities

An algorithm for the automatic detection and association of surface waves has been developed and tested over an 18 month interval on broad band data from the Yellowknife array (YKA). The detection algorithm uses a conventional STA/LTA scheme on data that have been narrow band filtered at 20 s periods and a test is then applied to identify dispersion. An average of 9 surface waves are detected daily using this technique. Beamforming is applied to determine the arrival azimuth; at a nonarray station this could be provided by poIarization analysis. The detected surface waves are associated daily with the events located by the short period array at Yellowknife, and later with the events listed in the USGS NEIC Monthly Summaries. Association requires matching both arrival time and azimuth of the Rayleigh waves. Regional calibration of group velocity and azimuth is required. . Large variations in both group velocity and azimuth corrections were found, as an example, signals from events in Fiji Tonga arrive with apparent group velocities of 2.9 3.5 krn/s and azimuths from 5 to + 40 degrees clockwise from true (great circle) azimuth, whereas signals from Kuriles Kamchatka have velocities of 2.4 2.9 km/s and azimuths off by 35 to 0 degrees. After applying the regional corrections, surface waves are considered associated if the arrival time matches to within 0.25 km/s in apparent group velocity and the azimuth is within 30 degrees of the median expected. Over the 18 month period studied, 32% of the automatically detected surface waves were associated with events located by the Yellowknife short period array, and 34% (1591) with NEIC events; there is about 70% overlap between the two sets of events. Had the automatic detections been reported to the USGS, YKA would have ranked second (after LZH) in terms of numbers of associated surface waves for the study period of April 1991 to September 1992.

scholarly journals Rayleigh Wave Dispersion for a Single Layer on an Elastic Half Space

1960 ◽  
Vol 13 (3) ◽  
pp. 498 ◽  
Author(s):  
BA Bolt ◽  
JC Butcher
Keyword(s):  
Numerical Solutions ◽  
Single Layer ◽  
Wave Dispersion ◽  
Elastic Half Space ◽  
Seismic Parameters ◽  
Period Equation ◽  
Phase And Group Velocities ◽  
The University ◽  
Rayleigh Wave Dispersion ◽  
Group Velocities

Numerical solutions of the period equation for Rayleigh waves in a single surface layer were calculated using the SILLIAC computer at the University of Sydney. Values of the phase and group velocities for both the fundamental and first higher mode are tabulated against period for eleven models. These related models allow a sensitivity analysis of the effect of variation in the seismic parameters.

Rayleigh wave group velocities in central California

1968 ◽  
Vol 58 (3) ◽  
pp. 881-890
Author(s):  
D. J. Sutton
Keyword(s):  
Rayleigh Wave ◽  
Group Velocity ◽  
Sierra Nevada ◽  
Wave Dispersion ◽  
Wave Group ◽  
Period Range ◽  
Central California ◽  
Great Valley ◽  
Rayleigh Wave Dispersion ◽  
Group Velocities

abstract Experimentally determined Rayleigh-wave dispersion curves of group velocity are given for five paths from NTS to stations in the network operated by the Seismographic Station at U.C. Berkeley. Periods observed range from 4 to 14 seconds. Although, as expected, two different paths from NTS to the western edge of the Sierra Nevada resulted in similar curves, efforts to find empirical curves appropriate to the Great Valley and the Coast Ranges on the assumption of provinces with parallel boundaries were not successful. Estimates of group velocity across the Great Valley along the path NTS to BRK indicate velocities, in the period range 5–9 seconds, considerably lower than would be expected from crustal models so far suggested.

Leaking modes and the PL phase

1960 ◽  
Vol 50 (2) ◽  
pp. 165-180
Author(s):  
Jack Oliver ◽  
Maurice Major
Keyword(s):  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Wave Train ◽  
Wave Dispersion ◽  
P Wave ◽  
Wave Guide ◽  
Mode Propagation ◽  
Near Surface ◽  
Surface Particle ◽  
Rayleigh Wave Dispersion

ABSTRACT The PL phase is a normally dispersed train of waves of periods greater than about 10 seconds beginning at or near the time of the initial P wave and sometimes continuing at least to the time of the beginning of the Rayleigh-wave train. With adequate instrumentation the PL phase is commonly observed at distances less than about 25° from shallow shocks. In general, surface particle motion is elliptical and progressive, and amplitudes are not greater than about one-quarter those of Rayleigh waves of the same period. Comparison of PL- and Rayleigh-wave dispersion shows that both waves propagate in roughly the same near-surface wave guide. Whereas Rayleigh waves correspond to normal- (nonleaking-) mode propagation, PL waves appear to correspond to leakingmode propagation within this wave guide.

Estimating the Hypocenter and Mechanism of the August 15, 1991 Centre Hall, Pennsylvania Earthquake Using Single-Station Data

1992 ◽  
Vol 63 (4) ◽  
pp. 541-555 ◽  
Author(s):  
Robert H. Clouser
Keyword(s):  
Wave Dispersion ◽  
Velocity Model ◽  
P Wave ◽  
Digital Data ◽  
Source Depth ◽  
Axis Orientation ◽  
Station Data ◽  
Short Period ◽  
Single Station ◽  
Back Azimuth

Abstract On August 15, 1991 a small (mbLg = 3.0) earthquake occurred near the town of Centre Hall, Pennsylvania. Based on early reports of felt effects and earthquake-generated sounds, the epicenter was placed somewhere ENE of State College, Pennsylvania. Three-component short-period digital data from the DWWSSN station SCP were analyzed to determine the hypocenter. Often, for small earthquakes in regions without dense seismic networks, information about an event must be obtained from single-station data. In this case, since no shallow velocity model exists for the area, simple ideas of wave propagation are invoked to estimate the distance and back-azimuth to the event. The horizontal P-wave particle motion constrained the back-azimuth, after calibrating the horizontal components by measuring the back-azimuth of quarry blast P-waves of known location. Distance determination was hampered by lack of a detailed upper crustal velocity model. Using iterative forward waveform modeling, a velocity model was generated that fit the observed S-minus-P and Rg-minus-P times and Rg-wave dispersion, and which was consistent with known upper crustal velocities in the area. A source depth of less than 1 km was inferred from the Rg-to-S ratio, the depth phase sP, and reports of earthquake-generated sounds. Estimates of the focal mechanism were obtained by a grid search procedure using Green’s functions computed with wavenumber integration for shear dislocation sources. Theoretical and observed amplitudes of sP, direct SH and SV (taken as ratios to the direct P), along with P polarity were compared for all possible combinations of strike, dip, and rake. Though fault plane orientation is poorly constrained, E-W to WNW-ESE P-axis orientation is a robust result of the search. Normal-faulting mechanisms are inconsistent with the data. However, the theoretical SV-to-P ratio is up to a factor of two larger than the observed ratio. This is probably related to an inadequate structure model and waveform sensitivity to source depth. Mechanism P-axis trends are consistent with other regional stress field indicators in the area.

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