Higher modes of continental Rayleigh waves

1957 ◽  
Vol 47 (3) ◽  
pp. 187-204 ◽  
Author(s):  
Jack Oliver ◽  
Maurice Ewing
Keyword(s):  
Wave Equation ◽  
Particle Motion ◽  
High Frequency ◽  
Rayleigh Waves ◽  
Velocity Curve ◽  
Theoretical Studies ◽  
Higher Modes ◽  
Short Period ◽  
First Time ◽  
Rayleigh Mode

ABSTRACT A long dispersive train of waves corresponding to higher modes of the Rayleigh-wave equation (including Sezawa's M2 wave) for the continental crust-mantle system is positively identified, apparently for the first time. Observed particle motion is elliptical and retrograde, in agreement with theory. Although several theoretical studies have been published in which progressive elliptical particle motion was found, all of these involved values of the elastic constants unsuitable for the present problem. The beginnings of the short-period branches of the higher modes can account for the high-frequency longitudinal and vertical components of the continental surface-wave phase Lg. The large amplitudes and the peculiar appearance of Rg appear to depend on the broad flat minimum of the group velocity curve of the lowest or Rayleigh mode.

Seismic velocity and Q model for the shallow structure of the Arabian shield from short‐period Rayleigh waves

Geophysics ◽  
1988 ◽  
Vol 53 (11) ◽  
pp. 1379-1387 ◽  
Author(s):  
T. A. Mokhtar ◽  
R. B. Herrmann ◽  
D. R. Russell
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Rayleigh Waves ◽  
Text Structure ◽  
Arabian Shield ◽  
Higher Modes ◽  
Dirac Delta ◽  
Short Period ◽  
Band Pass

The shear velocity and [Formula: see text] structure for the upper 1 km in different tectonic regions of the Arabian shield have been investigated using high‐frequency vertical component records of Rayleigh waves (1–20 Hz), which were recorded at source‐to‐receiver separations 55–80 km during a deep seismic refraction survey. Group and phase velocities of the fundamental and first higher modes were inverted for the shear‐wave velocity structure; Rayleigh‐wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the [Formula: see text] structure. Models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface‐wave theory with a center of compression used to represent the source; both band‐pass filtered step and Dirac delta source time functions were tested. Modeling indicates that the shear‐wave velocity of the shield increases from 2.6 km/s to 3.4 km/s in the upper 400 m of the crust. [Formula: see text] increases from 30 in the upper 50 m to 150 at 500 m depth. The underlying material has a [Formula: see text] of 400–500 for the out‐cropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock. A band‐pass filtered Dirac delta source time function produces the synthetic that is the best fit with observations.

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.

scholarly journals Hearing from the ocean and into the river: the evolution of the inner ear of Platanistoidea (Cetacea: Odontoceti)

Paleobiology ◽  
2021 ◽  
pp. 1-21
Author(s):  
Mariana Viglino ◽  
Maximiliano Gaetán ◽  
Mónica R. Buono ◽  
R. Ewan Fordyce ◽  
Travis Park
Keyword(s):  
Inner Ear ◽  
High Frequency ◽  
Sound Production ◽  
Marine Species ◽  
Late Oligocene ◽  
Evolutionary Patterns ◽  
Ear Morphology ◽  
Cochlear Morphology ◽  
First Time ◽  
Hearing Abilities

Abstract The inner ear of the two higher clades of modern cetaceans (Neoceti) is highly adapted for hearing infrasonic (mysticetes) or ultrasonic (odontocetes) frequencies. Within odontocetes, Platanistoidea comprises a single extant riverine representative, Platanista gangetica, and a diversity of mainly extinct marine species from the late Oligocene onward. Recent studies drawing on features including the disparate tympanoperiotic have not yet provided a consensus phylogenetic hypothesis for platanistoids. Further, cochlear morphology and evolutionary patterns have never been reported. Here, we describe for the first time the inner ear morphology of late Oligocene–early Miocene extinct marine platanistoids and their evolutionary patterns. We initially hypothesized that extinct marine platanistoids lacked a specialized inner ear like P. gangetica and thus, their morphology and inferred hearing abilities were more similar to those of pelagic odontocetes. Our results reveal there is no “typical” platanistoid cochlear type, as the group displays a disparate range of cochlear anatomies, but all are consistent with high-frequency hearing. Stem odontocete Prosqualodon australis and platanistoid Otekaikea huata present a tympanal recess in their cochlea, of yet uncertain function in the hearing mechanism in cetaceans. The more basal morphology of Aondelphis talen indicates it had lower high-frequency hearing than other platanistoids. Finally, Platanista has the most derived cochlear morphology, adding to evidence that it is an outlier within the group and consistent with a >9-Myr-long separation from its sister genus Zarhachis. The evolution of a singular sound production morphology within Platanistidae may have facilitated the survival of Platanista to the present day.

Direct measurement of air and precipitation particle motion by very high frequency Doppler radar

Nature ◽  
1985 ◽  
Vol 316 (6030) ◽  
pp. 712-714 ◽  
Author(s):  
S. Fukao ◽  
K. Wakasugi ◽  
T. Sato ◽  
S. Morimoto ◽  
T. Tsuda ◽  
...  
Keyword(s):  
Direct Measurement ◽  
Particle Motion ◽  
High Frequency ◽  
Doppler Radar ◽  
Very High Frequency ◽  
Very High

Estimating contribution of high-frequency sea-level oscillations to the extreme sea levels in the Adriatic Sea

2021 ◽  
Author(s):  
Krešimir Ruić ◽  
Jadranka Šepić ◽  
Maja Karlović ◽  
Iva Međugorac
Keyword(s):  
Time Series ◽  
Sea Level ◽  
High Frequency ◽  
Adriatic Sea ◽  
Tide Gauge ◽  
Data Series ◽  
Sea Levels ◽  
Short Period ◽  
Extreme Sea Levels ◽  
Sea Level Oscillations

<p>Extreme sea levels are known to hit the Adriatic Sea and to occasionally cause floods that produce severe material damage. Whereas the contribution of longer-period (T > 2 h) sea-level oscillations to the phenomena has been well researched, the contribution of the shorter period (T < 2 h) oscillations is yet to be determined. With this aim, data of 1-min sampling resolution were collected for 20 tide gauges, 10 located at the Italian (north and west) and 10 at the Croatian (east) Adriatic coast. Analyses were done on time series of 3 to 15 years length, with the latest data coming from 2020, and with longer data series available for the Croatian coast. Sea level data were thoroughly checked, and spurious data were removed. </p><p>For each station, extreme sea levels were defined as events during which sea level surpasses its 99.9 percentile value. The contribution of short-period oscillations to extremes was then estimated from corresponding high-frequency (T < 2 h) series. Additionally, for four Croatian tide gauge stations (Rovinj, Bakar, Split, and Dubrovnik), for period of 1956-2004, extreme sea levels were also determined from the hourly sea level time series, with the contribution of short-period oscillations visually estimated from the original tide gauge charts.  </p><p>Spatial and temporal distribution of contribution of short-period sea-level oscillations to the extreme sea level in the Adriatic were estimated. It was shown that short-period sea-level oscillation can significantly contribute to the overall extremes and should be considered when estimating flooding levels. </p>

Short-period seismic noise

1967 ◽  
Vol 57 (1) ◽  
pp. 55-81
Author(s):  
E. J. Douze
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Waves ◽  
Deep Hole ◽  
Period Range ◽  
Short Period ◽  
The Subject ◽  
Hole Arrays

abstract This report consists of a summary of the studies conducted on the subject of short-period (6.0-0.3 sec period) noise over a period of approximately three years. Information from deep-hole and surface arrays was used in an attempt to determine the types of waves of which the noise is composed. The theoretical behavior of higher-mode Rayleigh waves and of body waves as measured by surface and deep-hole arrays is described. Both surface and body waves are shown to exist in the noise. Surface waves generally predominate at the longer periods (of the period range discussed) while body waves appear at the shorter periods at quiet sites. Not all the data could be interpreted to define the wave types present.

The structure of the Cincinnati arch as determined by short period Rayleigh waves

1969 ◽  
Vol 59 (1) ◽  
pp. 399-407
Author(s):  
Robert B. Herrmann
Keyword(s):  
Experimental Data ◽  
Theoretical Model ◽  
Layer Thickness ◽  
Rayleigh Waves ◽  
Layer Model ◽  
Depth Data ◽  
Short Period ◽  
Best Fitting ◽  
Good Agreement

Abstract The propagation of Rayleigh waves with periods of 0.4 to 2.0 seconds across the Cincinnati arch is investigated. The region of investigation includes southern Indiana and Ohio and northern Kentucky. The experimental data for all paths are fitted by a three-layer model of varying layer thickness but of fixed velocity in each layer. The resulting inferred structural picture is in good agreement with the known basement trends of the region. The velocities of the best fitting theoretical model agree well with velocity-depth data from a well in southern Indiana.

Higher Modes of Rayleigh Waves and Upper Mantle Structure

1972 ◽  
pp. 93-100 ◽  
Author(s):  
V. I. Frantsuzova ◽  
A. L. Levshin ◽  
G. V. Shkadinskaya
Keyword(s):  
Upper Mantle ◽  
Rayleigh Waves ◽  
Mantle Structure ◽  
Higher Modes ◽  
Upper Mantle Structure

scholarly journals Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952*

1954 ◽  
Vol 44 (3) ◽  
pp. 471-479
Author(s):  
Maurice Ewing ◽  
Frank Press
Keyword(s):  
Internal Friction ◽  
Rayleigh Waves ◽  
Shear Velocity ◽  
Velocity Curve ◽  
The Core ◽  
Long Period ◽  
A Value ◽  
The Earth ◽  
Dispersion Data ◽  
Kamchatka Earthquake

Abstract Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952, are analyzed. The new Palisades long-period vertical seismograph recorded orders R6–R15, the corresponding paths involving up to seven complete passages around the earth. The dispersion data for periods below 400 sec. are in excellent agreement with earlier results and can be explained in terms of the known increase of shear velocity with depth in the mantle. Data for periods 400-480 sec. indicate a tendency for the group velocity curve to level off, suggesting that these long waves are influenced by a low or vanishing shear velocity in the core. Deduction of internal friction in the mantle from wave absorption gives a value 1/Q = 370 × 10−5 for periods 250-350 sec. This is a little over half the value reported earlier for periods 140-215 sec.

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