An investigation of discriminants for events in Western USSR based on regional phases recorded at station Kabul

1981 ◽  
Vol 71 (1) ◽  
pp. 263-274
Author(s):  
Indra N. Gupta ◽  
J. A. Burnetti
Keyword(s):  
Group Velocity ◽  
Rayleigh Waves ◽  
Amplitude Ratio ◽  
Vertical Component ◽  
Maximum Amplitude ◽  
Amplitude Ratios ◽  
Nuclear Explosions ◽  
Short Period ◽  
Regional Phases ◽  
Group Velocities

abstract Short-period, vertical-component records at the WWSSN station, Kabul for 13 earthquakes and 8 nuclear explosions occurring within a region of efficient propagation of Lg are examined to explore the possibility of using ratios of amplitudes in different group velocity windows as a discriminant. Each seismogram is divided into 10 windows with boundaries representing Pn and group velocities of 6.0, 5.0, 4.5, 4.0, 3.8, 3.6, 3.4, 3.2, 3.0, and 2.8 km/sec. The first three windows include crustal phases Pn, Pg, and Sn, respectively, whereas the six windows from 4.0 to 2.8 km/sec encompass the expected group velocity of higher mode Rayleigh waves that include Lg. The ratio of the maximum amplitude before the arrival of Sn to the maximum amplitude thereafter is significantly larger for explosions than for earthquakes and provides the largest separation between earthquake and explosion populations. Considerable separation is also shown by amplitude ratios Pn/Lg and Pn/Pg. Amplitude ratios based on earlier- and later-arriving Lg phases and the amplitude ratio Sn/Lg show insignificant discrimination. The ratio (maximum before Sn)/(maximum after Sn) is expected to be a useful regional discriminant for events in the Western USSR.

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.

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.

scholarly journals Worldwide distribution of group velocity of mantle Rayleigh waves as determined by spherical harmonic inversion

1982 ◽  
Vol 72 (4) ◽  
pp. 1185-1194 ◽  
Author(s):  
Ichiro Nakanishi ◽  
Don L. Anderson
Keyword(s):  
Group Velocity ◽  
Rayleigh Waves ◽  
Least Squares Method ◽  
Active Regions ◽  
Northwestern Pacific ◽  
Regional Studies ◽  
Worldwide Distribution ◽  
Tectonically Active ◽  
Harmonic Inversion ◽  
Group Velocities

abstract We have determined the worldwide distribution of group velocity of mantle Rayleigh waves for periods between 100 and 300 sec without assuming any regionalization. Group slowness 1/u(θ, φ) is expressed by spherical harmonics, and the coefficients, up to angular order 7, have been determined from travel times of Rayleigh waves by a least-squares method. From these, u(θ, φ) has been synthesized. Since we cannot obtain information about the odd terms of the expansion from one circuit measurements around the world, we have used group velocities of mainly R2 and R3. The overall pattern of u(θ, φ) for periods between 100 and 200 sec is consistent with results of previous pure-path and regional studies. Group velocities for tectonically active regions are low, and those of the shields and the northwestern Pacific are high.

scholarly journals Ambient Seismic Noise Cross - correlation of Ambon Island and Surrounding Area, Eastern Indonesia: Preliminary Result

2021 ◽  
Vol 873 (1) ◽  
pp. 012023
Author(s):  
Muhammad Fachrul Rozi Kurniawan ◽  
Shindy Rosalia ◽  
Andri Dian Nugraha ◽  
Zulfakriza ◽  
David P Sahara ◽  
...  
Keyword(s):  
Green’S Function ◽  
Group Velocity ◽  
Green's Function ◽  
Rayleigh Waves ◽  
Cross Correlation ◽  
Vertical Component ◽  
Data Series ◽  
Surrounding Area ◽  
Empirical Green’S Function ◽  
Empirical Green's Function

Abstract The island of Ambon lies on complex tectonics, part of Banda Arc which is driven by the Australia – Eurasia collision. Historical earthquake data show that an earthquake resulting the greatest tsunami in Indonesia had occurred at Ambon Island. On 26 September 2019, Ambon was shaken by an M 6.5 earthquake at a depth of 10 km (BMKG). In this study, we use ambient noise data from 11 temporary stations deployed by ITB and 4 permanent stations owned BMKG which are recorded from October until December 2019. Here, we purely use the vertical component of seismogram to retrieve the Empirical Green’s Function of Rayleigh waves. Cross-correlations were obtained from the daily data series and stacked the day-by-day cross-correlation data into one inter-station cross-correlation. The Empirical Green’s Function is seen at the band period 1-15 s. As a part of our study, we analyze the Green’s Function with frequency-time analysis (FTAN) to get Rayleigh wave group velocity. The group velocity of Rayleigh waves varies from 1.04 km/s – 3.75 km/s. Low group velocity might be indicated the presence of sediment or volcanic deposits and high group velocity might be indicated metamorphic rocks. The result of this study might give a finer velocity model of the shallow crustal beneath Ambon Island and the surrounding area.

scholarly journals Group Velocity Measurements of Earthquake Rayleigh Wave by S Transform and Comparison with MFT

2020 ◽  
Vol 24 (1) ◽  
pp. 91-95
Author(s):  
Chanjun Jiang ◽  
Youxue Wang ◽  
Gaofu Zeng
Keyword(s):  
Rayleigh Wave ◽  
Group Velocity ◽  
Rayleigh Waves ◽  
Accurate Method ◽  
Gaussian Filter ◽  
Velocity Measurements ◽  
Filter Parameter ◽  
S Transform ◽  
Real Earthquake ◽  
Group Velocities

Based upon the synthetic Rayleigh wave at different epicentral distances and real earthquake Rayleigh wave, S transform is used to measure their group velocities, compared with the Multiple Filter Technique (MFT) which is the most commonly used method for group-velocity measurements. When the period is greater than 15 s, especially than 40 s, S transform has higher accuracy than MFT at all epicenter distances. When the period is less than or equal to 15 s, the accuracy of S transform is lower than that of MFT at epicentral distances of 1000 km and 8000 km (especially 8000 km), and the accuracy of such two methods is similar at the other epicentral distances. On the whole, S transform is more accurate than MFT. Furthermore, MFT is dominantly dependent on the value of the Gaussian filter parameter α, but S transform is self-adaptive. Therefore, S transform is a more stable and accurate method than MFT for group velocity measurement of earthquake Rayleigh waves.

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.

Rayleigh waves in short-period seismic noise

1964 ◽  
Vol 54 (4) ◽  
pp. 1197-1212
Author(s):  
E. J. Douze
Keyword(s):  
Rayleigh Waves ◽  
Seismic Noise ◽  
Vertical Component ◽  
Density Functions ◽  
Power Spectral ◽  
Short Period ◽  
Seismic Surface Waves ◽  
Spectral Density Functions ◽  
Unique Variation ◽  
Good Agreement

Abstract Operation of short-period vertical seismometers at depths down to 3000 m in abandoned oil wells provides a new method of studying seismic surface waves. Power spectral density functions and the cross-products of simultaneous noise samples at the surface and at depth are used to obtain the change in amplitude and phase with depth. The vertical component of the noise is shown to be caused mainly by fundamental and higher mode Rayleigh waves. The fundamental, first, and third Rayleigh modes are identified in the noise. Each higher mode can be identified by its unique variation in displacement with depth and the 180-deg phase shifts that occur at the nodal points. The experimentally determined displacement of the different Rayleigh modes with depth is in good agreement with the theoretical displacement.

ESTIMATION OF SEISMIC NOISE STRUCTURE USING ARRAYS

Geophysics ◽  
1969 ◽  
Vol 34 (1) ◽  
pp. 21-38 ◽  
Author(s):  
R. T. Lacoss ◽  
E. J. Kelly ◽  
M. N. Toksöz
Keyword(s):  
Spectral Density ◽  
Fundamental Mode ◽  
Rayleigh Waves ◽  
Seismic Noise ◽  
Body Wave ◽  
Asymptotic Properties ◽  
Vertical Component ◽  
Body Waves ◽  
Low Frequencies ◽  
Short Period

A theoretical study of the use of arrays for the analysis of seismic noise fields has been completed. The frequency‐wavenumber power spectral density [Formula: see text] is defined and techniques for estimating it are given. The estimates require that the auto‐ and crosspower spectral densities be estimated for all elements in the array. Subject to certain asymptotic properties of these auto‐ and crosspower spectral density estimates, expressions for both the mean and variance of the estimates of [Formula: see text] have been obtained. It has been demonstrated that if [Formula: see text] is estimated by the Frequency Domain Beamforming Method, then the estimate has the same stability as the estimates of auto‐ and crosspower spectral density. [Formula: see text] has been estimated from both long‐ and short‐period noise recorded by the Large Aperture Seismic Array in Montana. At frequencies higher than 0.3 Hz, a compressional body‐wave component which correlates with atmospheric disturbances over distant oceans has been detected. In the frequency range of 0.2 and 0.3 Hz both body waves and higher mode Rayleigh waves are observed. At frequencies below 0.15 Hz the organized vertical component of microseisms consists primarily of fundamental mode Rayleigh waves. Appreciable amounts of fundamental mode Love wave energy may also be present on horizontal instruments at these low frequencies.

scholarly journals Free Short-Period Internal Waves in the Arctic Seas of Russia

2020 ◽  
Vol 37 (6) ◽  
Author(s):  
А. A. Bukatov ◽  
N. M. Solovei ◽  
E. A. Pavlenko ◽  
◽  
◽  
...  
Keyword(s):  
Internal Waves ◽  
Vertical Structure ◽  
Barents Sea ◽  
World Ocean ◽  
Vertical Component ◽  
Maximum Amplitude ◽  
Liouville Theory ◽  
The Arctic ◽  
Arctic Seas ◽  
Short Period

Purpose. The aim of the work is to investigate vertical structure and phase characteristics of free shortperiod internal waves (IW), and to assess their dependence on density stratification in the Barents, Kara, Laptev and East Siberian seas. © Букатов А. А., Соловей Н. М., Павленко Е. А., 2021 МОРCКОЙ ГИДРОФИЗИЧЕСКИЙ ЖУРНАЛ том 37 № 6 2021 645 Methods and Results. Solving the main boundary problem of the Sturm-Liouville theory has resulted in calculating the amplitudes of velocity vertical component, own frequencies and periods of the first mode of internal waves. The density field was calculated using the reanalysis data (World Ocean Atlas 2018) on temperature and salinity for 1955–2017 with a resolution 0.25°× 0.25°. The relation between the internal waves’ vertical structure and dispersion features, and the density depth distribution was analyzed. It is shown that the averaged over the sea area depth of the maximum amplitude of the IW velocity vertical component in the Barents and Kara seas is ∼ 90 m in the mid winter and ∼ 75–80 m in summer, and in the Laptev and East Siberian seas – ∼ 60 m throughout the whole year. Conclusions. In the months when the density gradients are maximal, the internal waves of the highest frequency and the shortest period are observed. The maximum water stability in the Barents Sea takes place in July – August, in the Kara Sea – in July – September and November, in the Laptev Sea – in June, November, and in the East Siberian Sea – in July. Just in the same months, the maximum values of the averaged own frequencies, and the minimum values of the averaged own periods and amplitudes of the vertical component of the internal waves’ velocity are observed.

Rayleigh wave synthetic seismograms from multi-dimensional simulations of underground explosions

1982 ◽  
Vol 72 (1) ◽  
pp. 15-28
Author(s):  
Thomas C. Bache ◽  
Steven M. Day ◽  
Henry J. Swanger
Keyword(s):  
Free Surface ◽  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Material Behavior ◽  
Earth Model ◽  
Far Field ◽  
Two Dimensional ◽  
Nuclear Explosions ◽  
Short Period ◽  
Source Wave

abstract A general method is presented for coupling the near-source wave fields, obtained from time-stepping numerical calculations, with analytically formulated methods for continuing the wave field to larger ranges. The source calculation may include a free surface and other material boundaries as well as arbitrary material behavior, as long as it is carried into a region where the material response is linearly elastic. The method, which is based on an elastodynamic representation theorem, is worked out in detail for the Rayleigh wave modes for an axisymmetric source in a plane-layered earth model and is demonstrated by a sample calculation for which the exact solution is known. Two realistic, axisymmetric simulations of nuclear explosions (20 and 150 kt at 1-km depth) are studied to estimate the effect of nonlinear interactions with the free surface on the far-field Rayleigh waves. The importance of these two-dimensional phenomena is quantified by comparing far-field Rayleigh waves computed from these simulations with Rayleigh waves computed from analogous one-dimensional (spherically symmetric) simulations. While the two-dimensional simulations exhibit substantial spallation associated with the free surface, the predicted effect on the Rayleigh wave peak amplitudes is negligible. Two-dimensional effects also alter the waveform very little, apart from some enhancement of very short-period components for the larger explosion.

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