Scattering of long-period Rayleigh waves in Western North America and the interpretation of coda Q measurements

1989 ◽  
Vol 79 (3) ◽  
pp. 774-789
Author(s):  
Charles A. Langston
Keyword(s):  
North America ◽  
Rayleigh Wave ◽  
Energy Flux ◽  
Rayleigh Waves ◽  
Western North America ◽  
Coda Q ◽  
Long Period ◽  
Anelastic Attenuation ◽  
Short Period ◽  
Flux Model

Abstract The codas of long-period Rayleigh waves recorded at WWSSN and Canadian network stations in Western North America from eight underground explosions at NTS are examined in an effort to separate scattering and anelastic attenuation effects. Coda behavior of 0.1 and 0.2 hz Rayleigh waves follows coda characteristics seen in studies of short-period S waves. Coda decay rate is seen to be a stable observation over most stations in Western North America and is consistent with the hypothesis that backscattered surface waves from heterogeneities contained within the western half of the continent form the Rayleigh wave coda. The basic data observables of coda level and decay are interpreted using several plausible models. The single scattering model yields a coda Q consistent with previously determined Rayleigh anelastic attenuation coefficients. Separation of anelastic and scattering Q is possible using an energy flux model and shows that scattering Q is one to two orders of magnitude higher than anelastic Q. However, an energy flux model that incorporates a layer of scatterers over a homogeneous half-space shows that all Rayleigh-wave attenuation can be explained purely by scattering effects which include Rayleigh- to body-wave conversion. Coda can be fit equally well by these mutually incompatible models. It is not likely that the mechanisms of scattering or anelastic attenuation can be addressed by coda observations of a single homogeneous data set.

Small Earthquakes and Explosions in Western North America recorded by New High Gain, Long Period Seismographs

Nature ◽  
1969 ◽  
Vol 224 (5226) ◽  
pp. 1268-1273 ◽  
Author(s):  
PETER MOLNAR ◽  
JOHN SAVINO ◽  
LYNN R. SYKES ◽  
ROBERT C. LIEBERMANN ◽  
GEORGE HADE ◽  
...  
Keyword(s):  
North America ◽  
High Gain ◽  
Western North America ◽  
Long Period

GULF COAST SURFACE WAVES

Geophysics ◽  
1953 ◽  
Vol 18 (1) ◽  
pp. 41-53 ◽  
Author(s):  
Lynn G. Howell ◽  
E. F. Neuenschwander ◽  
A. L. Pierson
Keyword(s):  
Rayleigh Wave ◽  
Surface Waves ◽  
Velocity Dispersion ◽  
Gulf Coast ◽  
Group Velocity Dispersion ◽  
Vertical Strain ◽  
Long Period ◽  
Short Period ◽  
Component Velocity ◽  
Wave Trains

Surface wave recordings were made with the following: a three‐component velocity seismometer, a long‐period displacement seismometer, six dynamic seismometers, an air‐actuated condenser microphone, and a vertical strain seismometer. Wave trains were recorded similar to those obtained by B. F. Howell in California. We have divided the surface waves into two trains instead of three. The early train seems to have properties of the M‐2 wave of Sezawa; the late train seems to be a Rayleigh wave. An air‐coupled wave is shown to be associated with the M‐2 wave. In the group velocity dispersion curve of the Rayleigh wave, the short‐period branch was found as predicted by theory as well as the usually observed long‐period branch. By making certain assumptions, the thickness of the top layer appears to be about 50 feet according to the theoretical curves of Kanai.

Surface-wave magnitudes of Eurasian earthquakes and explosions

1975 ◽  
Vol 65 (3) ◽  
pp. 693-709 ◽  
Author(s):  
Otto W. Nuttli ◽  
So Gu Kim
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Rayleigh Waves ◽  
Body Wave ◽  
Focal Depth ◽  
Vertical Component ◽  
P Waves ◽  
Long Period ◽  
Short Period ◽  
Continental Interior

abstract Body-wave magnitudes, mb, and surface-wave magnitudes, MS, were determined for approximately 100 Eurasian events which occurred during the interval August through December 1971. Body-wave magnitudes were determined from 1-sec P waves recorded by WWSSN short-period, vertical-component seismographs at epicentral distances greater than 25°. Surface-wave magnitudes were determined from 20-sec Rayleigh waves recorded by long-period, vertical-component WWSSN and VLPE seismographs. The earthquakes had mb values ranging from 3.6 to 5.7. Of 96 presumed earthquakes studied, 6 lie in or near the explosion portion of an mb:MS plot. The explosion mb:MS curve was obtained from seven Eurasian events which had mb values ranging from 5.0 to 6.2 and MS values from 3.2 to 5.1. All six anomalous earthquakes were located in the interior of Asia, in Tibet, and in Szechwan and Sinkiang provinces of China. In general, oceanmargin earthquakes were found to have more earthquake-like mb:MS values than those occurring in the continental interior. Neither focal depth nor focal mechanism can explain the anomalous events.

Surface-wave constraints on the August 1, 1975, Oroville earthquake

1977 ◽  
Vol 67 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Robert S. Hart ◽  
Rhett Butler ◽  
Hiroo Kanamori
Keyword(s):  
Surface Wave ◽  
Rayleigh Waves ◽  
Body Wave ◽  
Source Parameters ◽  
The Body ◽  
Wave Radiation ◽  
Spectral Amplitude ◽  
Surface Wave Magnitude ◽  
Long Period ◽  
Short Period

abstract Observations of Love and Rayleigh waves on WWSSN and Canadian Network seismograms have been used to place constraints upon the source parameters of the August 1, 1975, Oroville earthquake. The 20-sec surface-wave magnitude is 5.6. The surface-wave radiation pattern is consistent with the fault geometry determined by the body-wave study of Langston and Butler (1976). The seismic moment of this event was determined to be 1.9 × 1025 dyne-cm by both time-domain and long-period (T ≥ 50 sec) spectral amplitude determinations. This moment value is significantly greater than that determined by short-period studies. This difference, together with the low seismic efficiency of this earthquake, indicates that the character of the source is intrinsically different at long periods from those aspects which dominate the shorter-period spectrum.

Rayleigh wave dispersion in the Pacific Ocean for the period range 20 to 140 seconds

1962 ◽  
Vol 52 (2) ◽  
pp. 333-357 ◽  
Author(s):  
John Kuo ◽  
James Brune ◽  
Maurice Major
Keyword(s):  
Phase Velocity ◽  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Initial Phase ◽  
Velocity Curve ◽  
Period Range ◽  
Long Period ◽  
Phase Velocities ◽  
The Pacific ◽  
Group Velocities

ABSTRACT Rayleigh wave data obtained from Columbia long-period seismographs installed during the International Geophysical Year (I.G.Y.) at Honolulu, Hawaii; Suva, Fiji; and Mt. Tsukuba, Japan, are analyzed to determine group and phase velocities in the Pacific for the period range 20 to 140 seconds. Group velocities are determined by usual techniques (Ewing and Press, 1952, p. 377). Phase velocities are determined by assuming the initial phase to be independent of period and choosing the initial phase so that the phase velocity curve agrees in the long period range with the phase velocity curve of the mantle Rayleigh wave given by Brune (1961). Correlations of wave trains between the stations Honolulu and Mt. Tsukuba are used to obtain phase velocity values independent of initial phase. The group velocity rises from 3.5 km/sec at a period of about 20 see to a maximum of 4.0 km/sec at a period of about 40 sec and then decreases to 3.65 km/sec at a period of about 140 sec. Phase velocity is nearly constant in the period range 30–75 sec with a value slightly greater than 4.0 km/sec. Most of the phase velocity curves indicate a maximum and a minimum at periods of approximately 30 and 50 sec respectively. At longer periods the phase velocities increase to 4.18 km/sec at a period of 120 sec. Except across the Melanesian-New Zealand region, dispersion curves for paths of Rayleigh waves throughout the Pacific basin proper are rather uniform and agree fairly well with theoretical dispersion curves for models with a normal oceanic crust and a low velocity channel. Both phase and group velocities are comparatively lower for the paths of Rayleigh waves across the Melanesian-New Zealand region, suggesting a thicker crustal layer and/or lower crustal velocities in this region.

Energy-flux model of seismic coda: Separation of scattering and intrinsic attenuation

1987 ◽  
Vol 77 (4) ◽  
pp. 1223-1251
Author(s):  
Arthur Frankel ◽  
Leif Wennerberg
Keyword(s):  
Decay Rate ◽  
Energy Flux ◽  
Single Scattering ◽  
Coda Q ◽  
Scattering Attenuation ◽  
Seismic Coda ◽  
Wide Range ◽  
Flux Model ◽  
Strong Scattering ◽  
Q Values

Abstract A new model of seismic coda is presented, based on the balance between the energy scattered from the direct wave and the energy in the seismic coda. This energy-flux model results in a simple formula for the amplitude and time decay of the seismic coda that explicitly differentiates between the scattering and intrinsic (anelastic) attenuation of the medium. This formula is valid for both weak and strong scattering and implicitly includes multiple scattering. The model is tested using synthetic seismograms produced in finite difference simulations of wave propagation through media with random spatial variations in seismic velocity. Some of the simulations also included intrinsic dissipation. The energy-flux model explains the coda decay and amplitude observed in the synthetics, for random media with a wide range of scattering Q. In contrast, the single-scattering model commonly used in the analysis of microearthquake coda does not account for the gradual coda decay observed in the simulations for media with moderate or strong scattering attenuation (scattering Q ≦ 150). The simulations demonstrate that large differences in scattering attenuation cause only small changes in the coda decay rate, as predicted by the energy-flux model. The coda decay rate is sensitive, however, to the intrinsic Q of the medium. The ratio of the coda amplitude to the energy in the direct arrival is a measure of the scattering attenuation. Thus, analysis of the decay rate and amplitude of the coda can, in principle, produce separate estimates for the scattering and intrinsic Q values of the crust. We analyze the coda from two earthquakes near Anza, California. Intrinsic Q values determined from these seismograms using the energy-flux model are comparable to coda Q values found from the single-scattering theory. These results indicate that coda Q values are, at best, measures of the intrinsic Q of the lithosphere and are unrelated to the scattering Q.

Dispersion of Rayleigh waves for purely oceanic paths in the Pacific

1969 ◽  
Vol 59 (5) ◽  
pp. 1905-1925
Author(s):  
Rodolfo Piermattei ◽  
Ali A. Nowroozi
Keyword(s):  
San Francisco ◽  
Rayleigh Waves ◽  
Group Velocity Dispersion ◽  
Dispersion Curves ◽  
Easter Island ◽  
Ocean Bottom ◽  
Long Period ◽  
The Pacific ◽  
Starting Point ◽  
Short Period

abstract Thirty-five shallow, distant earthquakes located in the Pacific and recorded at the Ocean Bottom Geophysical station OBS III by a long-period vertical seismograph and a long-period crystal hydrophone were selected for analysis of the dispersion of Rayleigh waves. The sensors are part of the Lamont Geological Observatory's instrument package implanted in May 1966 approximately 200 km west of San Francisco at a water depth of 3.9 km. The location of the station and that of the epicenters, all in the ocean, give us for the first time the oppurtunity of studying purely oceanic paths. The group velocity dispersion curves in the period range 12-40 sec show minor regional differences in the oceanic crustal structure. For the comparison, dispersion curves were obtained for 24 of these earthquakes from the seismographs recorded at the Berkeley seismograph station, BKS. Most of the pairs of dispersion curves show no significant differences due to crossing the continental margin. However, the group velocities of Rayleigh waves from southern Alaska and Easter Island are higher at OBS III than at Berkeley by as much as 0.1 km/sec. Realizing that theoretical models based exclusively on surface-wave data are not unique, and taking Dorman's oceanic model 8099 as our starting point, we were able to fit our experimental dispersion curves using models characterized by a low-velocity zone starting at a depth of about 60 km. According to this type of solution the crust is thicker along the paths from south Alaska and Easter Island, parallel to the coast, than along the other paths examined. The pressure-to-displacement ratio (P/D) is not very sensitive to changes in the models for periods greater than 12 sec. It is, however, useful in determining the local sedimentary structure from short-period waves.

Rayleigh Wave Propagation in the Bighorn Mountains Region, Wyoming

2021 ◽  
Author(s):  
Jonas A. Kintner ◽  
K. Michael Cleveland ◽  
Ryan Modrak ◽  
Audrey Dunham
Keyword(s):  
Wave Propagation ◽  
Surface Wave ◽  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Sedimentary Basins ◽  
Near Surface ◽  
Retrograde Motion ◽  
Explosion Monitoring ◽  
Short Period ◽  
Surface Geology

ABSTRACT Short-period Rayleigh waves, Rg, provide strong constraints on the depth of shallow seismic events and are of interest for monitoring small explosions. Characterizing the seismic sources that generate Rg requires an understanding of how shallow crustal structure affects Rayleigh wave propagation. In support of these efforts, this study utilizes observed waveforms from small shallow explosions recorded on temporary seismic network deployments in the Bighorn region, Wyoming. We study regional near-surface geology by measuring changes in surface-wave amplitude and polarization during propagation through basins, foothills, and mountains. We develop additional insight by carrying out surface-wave eigenfunction analyses and numerical-wave simulations, which together reproduce many characteristics seen in the observed waveforms. Our results show how sedimentary basins in the Bighorn region allow for amplified prograde-polarized higher-mode and retrograde-polarized fundamental-mode Rayleigh waves, whereas adjacent mountains only support retrograde motion. These different modes provide distinct constraints on the Earth structure and source characteristics, potentially enabling targeted inversions in future studies. Our findings provide insight into Rg propagation through complex near-surface geology, improving our understanding of shallow propagation and source effects that are relevant to explosion monitoring efforts.

scholarly journals Body-wave amplitude and travel-time correlations across North America

1983 ◽  
Vol 73 (4) ◽  
pp. 1063-1076
Author(s):  
Thorne Lay ◽  
Donald V. Helmberger
Keyword(s):  
North America ◽  
Travel Time ◽  
Body Wave ◽  
Rocky Mountain ◽  
S Wave ◽  
Arrival Times ◽  
S Waves ◽  
Long Period ◽  
Amplitude Data ◽  
Short Period

abstract Relationships between travel-time and amplitude station anomalies are examined for short- and long-period SH waves and short-period P waves recorded at North American WWSSN and Canadian Seismic Network stations. Data for two azimuths of approach to North America are analyzed. To facilitate intercomparison of the data, the S-wave travel times and amplitudes are measured from the same records, and the amplitude data processing is similar for both P and S waves. Short-period P- and S-wave amplitudes have similar regional variations, being relatively low in the western tectonic region and enhanced in the shield and mid-continental regions. The east coast has intermediate amplitude anomalies and systematic, large azimuthal travel-time variations. There is a general correlation between diminished short-period amplitudes and late S-wave arrival times, and enhanced amplitudes and early arrivals. However, this correlation is not obvious within the eastern and western provinces separately, and the data are consistent with a step-like shift in amplitude level across the Rocky Mountain front. Long-period S waves show no overall correlation between amplitude and travel-time anomalies.

scholarly journals An investigation of mantle Rayleigh waves*

1954 ◽  
Vol 44 (2A) ◽  
pp. 127-147
Author(s):  
Maurice Ewing ◽  
Frank Press
Keyword(s):  
Internal Friction ◽  
Upper Mantle ◽  
Rayleigh Waves ◽  
Normal Pressure ◽  
Crystalline Rocks ◽  
Velocity Curve ◽  
Continental Margins ◽  
Long Period ◽  
Short Period ◽  
Small Scatter

abstract Dispersion of Rayleigh waves for a new range of periods ranging from 1 to 7 minutes is described. The group velocity curve shows a long-period and a short-period branch merging at a minimum value of 3.54 km/sec. with a corresponding period of about 225 sec. It is suggested that the known variation of velocity with depth in the mantle can account for the observed dispersion. The small scatter in the velocities and the absorption of these waves suggests that, unlike shorter-period surface waves, refraction and attenuation effects are negligible at the continental margins. From the absorption of mantle Rayleigh waves the internal friction in the upper mantle for periods of 140 and 215 sec. is found to be given by 1/Q = 670 × 10−5. This is of the same order as that reported from vibration measurements at audio frequencies on laboratory samples of crystalline rocks at normal pressure and temperature.

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