Teleseismic p-wave transmission through slabs

1973 ◽  
Vol 63 (4) ◽  
pp. 1349-1373
Author(s):  
Norman H. Sleep
Keyword(s):  
P Wave ◽  
P Waves ◽  
Nuclear Explosions ◽  
Velocity Models ◽  
Shallow Earthquakes ◽  
Short Period ◽  
Systematic Effects ◽  
First Motion ◽  
Low Amplitude ◽  
Good Agreement

abstract Theoretical ray paths through velocity models constructed from numerically calculated thermal models of slabs were computed. The results were in good agreement with observed travel times. First motion amplitudes of P waves at teleseismic distances were measured from long- and short-period WWSSN records of intermediate focus earthquakes in the Tonga, Kermadec, and Kurile regions and of nuclear explosions and shallow earthquakes in the Aleutian region. These amplitudes were corrected for source mechanism. The Aleutian data were sufficient to show that intermediate focus earthquakes in that region occur in the colder regions of the slab. At short periods, for regions other than the Aleutians, shadowing effects which could be associated with the slab were not very marked, less than a factor of 2 reduction for epicentral distances between 30° and 50°. No systematic effects due to plates were found in the long-period data. Some stations in the predicted shadow zone of a Tonga earthquake recorded low amplitude precursors which probably were greatly defocused waves which ran the full length of the slab. Simple diffraction is incapable of explaining the short-period results.

Radial Velocity Variations in Cool Supergiants

1984 ◽  
Vol 88 ◽  
pp. 283-288
Author(s):  
Hugh C. Harris
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Short Period ◽  
Cool Stars ◽  
Synchronous Rotation ◽  
Red Supergiants ◽  
Velocity Variations ◽  
Orbital Periods ◽  
Low Amplitude ◽  
Good Agreement

AbstractA survey of F, G, and W supergiants has been carried out with the DAO radial velocity spectrometer, an efficient instrument for detecting low-amplitude velocity variations in cool stars. Observations of 78 stars over five seasons show generally good agreement with OORAVEL results for spectroscopie binaries. The majority of supergiants show low-amplitude variability, with amplitudes typically 1 to 2 km s−1. The width of the cross-correlation profile has been measured for 58 supergiants. It reveals 14 stars with unusually broad lines, indicative of rotation velocities of 15 to 35 km s−1. Several have short-period binary companions and may be in synchronous rotation. The other broad-lined stars are apparently single or with long orbital periods; they may be making their first transition from the main sequence to become red supergiants.

WIDE‐BAND EXTRACTION OF MANTLE P WAVES FROM AMBIENT NOISE

Geophysics ◽  
1964 ◽  
Vol 29 (5) ◽  
pp. 672-692 ◽  
Author(s):  
Milo Backus ◽  
John Burg ◽  
Dick Baldwin ◽  
Ed Bryan
Keyword(s):  
Ambient Noise ◽  
Wide Band ◽  
P Wave ◽  
Cumberland Plateau ◽  
P Waves ◽  
Single Output ◽  
Short Period ◽  
Multichannel Filtering ◽  
On Line ◽  
Element Array

The spatial correlation characteristics of ambient short‐period (0.5 to 5 cps) noise at Ft. Sill, Oklahoma, and on the Cumberland Plateau in Tennessee were investigated on “permanent” arrays with 3–4 kilometer diameter. Dominant ambient noise at the two locations is spatially organized, and to first order may be treated as a combination of seismic propagating wave trains. At the Tennessee location noise energy above one cps is dominantly propagating with velocities from 3.5 to 4.5 km/sec, and must be carried in deeply trapped, high‐order modes. Generalized multichannel filtering (Burg) can be used to preserve a large class of mantle P‐wave signals, wide‐band, in a single output trace, while at the same time specifically rejecting ambient noise on the basis of its organization. Results of generalized multichannel filtering applied on‐line at the nineteen‐element array in Tennessee and applied off‐line are discussed.

scholarly journals The effects of tectonic release on short-period P waves from NTS explosions

1984 ◽  
Vol 74 (3) ◽  
pp. 819-842
Author(s):  
Thorne Lay ◽  
Terry C. Wallace ◽  
Don V. Helmberger
Keyword(s):  
Frequency Component ◽  
Temporal Variations ◽  
P Wave ◽  
High Frequency Component ◽  
Stress Regime ◽  
P Waves ◽  
Underground Nuclear Explosions ◽  
Long Period ◽  
Short Period ◽  
Amplitude Pattern

Abstract The first cycle (ab amplitude) of teleseismic short-period P waves from underground nuclear explosions at Pahute Mesa (NTS) show a systematic azimuthal amplitude pattern that can possibly be explained by tectonic release. The amplitudes vary by a factor of three, with diminished amplitudes being recorded at azimuths around N25°E. This azimuthal pattern has a strong sin(2φ) component and is observed, to varying degrees, for 25 Pahute Mesa events, but not for events at other sites within the NTS. Events that are known to have large tectonic release have more pronounced sin(2φ) amplitude variations. A synthesis of long-period body and surface wave investigations of tectonic release for Pahute Mesa events shows that, in general, the nonisotropic radiation is equivalent to nearly vertical, right-lateral strike-slip faulting trending from N20°W to due north. Long-period P waves at upper mantle distances demonstrate that there is a significant high-frequency component to the tectonic release. Using the long-period constraints on orientation, moment, and frequency content of the tectonic release, the expected short-period P wave effects are predicted. For models in which the downgoing P wave from the explosion triggers tectonic release within a few kilometers below the shot point, a factor of 2.5 amplitude variation with azimuth is predicted for the short-period ab amplitudes, with the lowest amplitudes expected near N25°E. Rather subtle azimuthal variations in the waveforms are expected, particulary for downward propagating ruptures, which is consistent with the absence of strong variations in the data. The occurrence of the azimuthal pattern, albeit with varying strength, for all of the Pahute Mesa events suggests a tectonic release model in which the shatterzone surrounding the explosion cavity is extended preferentially downward by driving a distributed network of faults and joints underlying the Mesa several kilometers beneath the surface. In this model, all events could have a component of tectonic release which would reflect the regional stress regime, although there may be slight spatial and temporal variations in the tectonic release contribution. Some events may trigger slip on larger throughgoing faults as well. While it is shown that tectonic release can affect teleseismic short-period signals significantly, and may contribute to the Pahute Mesa amplitude pattern, other possible explanations are considered.

The El Asnam, Algeria, earthquake of 10 October 1980: Multiple-source mechanism determined from long-period records

1982 ◽  
Vol 72 (4) ◽  
pp. 1111-1128
Author(s):  
A. Deschamps ◽  
Y. Gaudemer ◽  
A. Cisternas
Keyword(s):  
Main Shock ◽  
Body Wave ◽  
P Wave ◽  
P Waves ◽  
Small Component ◽  
Long Period ◽  
The North ◽  
Complex Source ◽  
Dip Angle ◽  
Good Agreement

abstract We present a study of the El Asnam, Algeria, earthquake of 10 October 1980 from a large collection of long-period surface and body wave records. The focal mechanism of the main shock is well constrained by the P-wave first motions at teleseismic distances and field observations: it was a thrust event on a plane striking N45°E, and a dip angle of 54° to the north. It had a small component of left-lateral motion (λ = 83°) (Ouyed et al., 1981; Gaudemer et al., 1981). This earthquake was very well recorded on WWSSN stations and on GDSN and IDA digital stations, with a good azimuthal distribution. From these records, we confirm the focal solution and obtain a seismic moment Mo = 5 × 1026 dyne-cm. The P-wave seismograms indicate a complex source. We show that it is not sufficient to model the source by a multiple event, but it is also necessary to include a propagation effect in order to explain accurately the waveform. With assumptions based on field observation of the surface breaks, we model the P waves, including two discontinuities of the propagation, along the fault plane and obtain a good agreement of the waveform.

A source theory for complex earthquakes

1975 ◽  
Vol 65 (5) ◽  
pp. 1385-1405 ◽  
Author(s):  
R. R. Blandford
Keyword(s):  
Fault Plane ◽  
Amplitude Ratio ◽  
P Wave ◽  
Corner Frequency ◽  
Transform Faults ◽  
Shallow Earthquakes ◽  
Short Period ◽  
Wave Forms ◽  
The Moment ◽  
Third Moment

Abstract Earthquake source theories of Haskell, Brune, and Savage have been drawn upon to develop a description of an earthquake as a major slip accompanied by many smaller tensional and slip events. We find natural explanations of several previously unexplained observations, such as: Robustness of the MS: mb discriminant, P corner frequency higher than S corner frequency for shallow earthquakes, High-frequency P/S amplitude ratio higher for shallow earthquakes than previous theories predict, Increase of complexity as a function of third moment, Small mb relative to MS for transform faults. (This can also be explained by emergent short-period P wave forms or by a low-Q region underlying the source). The theory predicts that MS:mb populations of earthquakes and explosions will not converge at small magnitudes. The theory also suggests that the standard interpretations of corner-frequency measurements can provide only a lower limit to fault-plane dimensions and, in combination with the moment, only an upper limit on stress drop.

Seismic magnitudes of underground nuclear explosions

1973 ◽  
Vol 63 (1) ◽  
pp. 105-131 ◽  
Author(s):  
P. W. Basham ◽  
R. B. Horner
Keyword(s):  
Computational Procedure ◽  
Test Site ◽  
P Wave ◽  
Nevada Test Site ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Novaya Zemlya ◽  
Yield Information ◽  
Short Period ◽  
Propagation Effects

abstract Using an Ms computational procedure that minimizes path-propagation effects, and with Ms values found to be empirically independent of test site and detonation medium among consolidated rock explosions, available yield information is employed to illustrate that the seismic scaling of explosions in realistic detonation environments produces teleseismic Rayleigh-wave displacements proportional to the 1.2-power of yield over the range from low yields to greater than three megatons. Ms values independent of network, path, and site can be employed to estimate unknown yields at uncalibrated test sites to within average errors judged to be about 20 per cent. P-wave magnitudes, in the form of a calibrated teleseismic measure of short-period P-wave displacements, show a theoretically supported dependence of displacement on the 1.1-power of yield over the range from 6 kt to 1 mt. Studied explosions separate into two categories: the Nevada Test Site granite explosions, LONG SHOT, the Sahara February 1965 explosion and (by empirical inference) Novaya Zemlya and Eastern Kazakh explosions exhibit P-wave displacements about a factor of 3 greater than explosions of the same yield in tuff, rhyolite, and shale. P-wave magnitudes of explosions are subject to such a diversity of source, propagation, and measurement phenomena that any estimation of unknown yields without a closely controlled site and network calibration can be subject to large errors.

Multivariate autoregressive representation of seismic P-wave signals with application to short-period discrimination

1978 ◽  
Vol 68 (3) ◽  
pp. 735-756 ◽  
Author(s):  
Ottar Sandvin ◽  
Dag Tjøstheim
Keyword(s):  
Time Series ◽  
Parametric Models ◽  
P Wave ◽  
Separate Analysis ◽  
Wave Signal ◽  
Nuclear Explosions ◽  
Spectral Density Matrix ◽  
Short Period ◽  
Vector Time Series ◽  
Multivariate Autoregressive

abstract It is shown that seismic P-wave vector signals as recorded by selected NORSAR subarrays can be described by multivariate parametric models of autoregressive type. These are models having the form X ¯ ( t ) − A 1 X ¯ ( t − 1 ) − ... − A p X ¯ ( t − p ) = W ¯ ( t ) Where X¯(t) (t) is the digitized short-period vector time series defined by the P-wave signal and W¯(t) (t) is a white noise vector time series. The multivariate autoregressive analysis is undertaken for 83 nuclear explosions and 72 earthquakes from Eurasia. For each event a separate analysis of the main signal and of the coda has been carried through. It is found that in most cases a reasonable statistical fit is obtained using a low-order autoregressive model. The autoregressive parameters characterize the spectral density matrix of the P-wave signal and therefore form a convenient basis for constructing short-period discriminants between earthquakes and explosions. Based on the classification results for our data base of Eurasian events, we find that the multivariate autoregressive parameters have a substantially larger discrimination potential than the short-period parameters suggested earlier in the literature. In fact our results indicate that, based on autoregressive parameters, it may now be possible to construct purely short-period discriminants which are comparable, if not superior, to the mb:Ms criterion.

Spectral and magnitude characteristics of anomalous Eurasian earthquakes

1977 ◽  
Vol 67 (2) ◽  
pp. 463-478
Author(s):  
So Gu Kim ◽  
Otto W. Nuttli
Keyword(s):  
Focal Mechanism ◽  
Rayleigh Waves ◽  
Main Shock ◽  
Focal Depth ◽  
P Wave ◽  
Wave Spectra ◽  
P Waves ◽  
Aftershock Sequences ◽  
Short Period ◽  
Amplitude Spectra

Abstract A number of main shock-aftershock sequences in the Eurasian interior contain some aftershocks whose mb:MS values are close to those of underground explosions. This paper is concerned with a study of the amplitude spectra of the P waves and Rayleigh waves for earthquakes of those main shock-aftershock sequences. It is found that for any given sequence studied, there is little if any variation in focal depth or focal mechanism. This rules out variations in these quantities as being the cause of anomalous mb:MS values. A study of the P-wave spectra establishes that one or both of the corner periods of anomalous earthquakes are smaller than those of non-anomalous earthquakes of the same moment. Thus the cause of anomalous mb:MS values of the earthquakes studied is a relative enrichment of the short-period portion of the spectrum of the anomalous events, which cannot be attributed to focal depth or focal mechanism.

The relative performance of mb and alternative measures of elastic energy in estimating source size and explosion yield

1984 ◽  
Vol 74 (5) ◽  
pp. 1863-1882
Author(s):  
J. T. Bullitt ◽  
V. F. Cormier
Keyword(s):  
Elastic Energy ◽  
P Wave ◽  
Reference Station ◽  
Small Data ◽  
Federal Republic Of Germany ◽  
Underground Nuclear Explosions ◽  
Nuclear Explosions ◽  
Short Period ◽  
Alternative Measures ◽  
The Stability

Abstract A comparison has been made of the relative scatter of classical mb and alternative measures of P-wave energy from underground nuclear explosions at test sites in East Kazakh, USSR. The scatter of the energy measures is observed in teleseismic arrays of short-period Global Digital Seismic Network (GDSN) stations and the local broadband array at Graefenburg, Federal Republic of Germany. Four measures of A in log(A/T), spectral magnitudes, peak velocity, rms coda, and integrated velocity-squared are compared. The measures are constructed to be in equivalent units of the flux rate of radiated elastic energy. All measures are assumed to have the same slope in a linear regression of log(yield) versus log(measure). Three independent tests were made of the stability of the yield estimators: the scatter of the measures using: (1) Graefenburg array data; (2) GDSN data normalized to a reference station; and (3) GDSN data normalized to a reference event. The differences among the standard deviations are small (≦ 0.1 mb units), making it difficult using a small data base to conclude whether the performance of one estimator is significantly better than another. The relative order in the performance of the yield estimators, however, is preserved in each of the three tests. The coda measure is the most stable, followed by the spectral and time-domain A/T measures. The relations observed at Graefenburg between (1) the amplitude of direct P versus P coda, (2) the apparent azimuth of direct P, and (3) complexity, suggest that amplitude variations across an array are a product of scattering along the entire ray path as well as scattering, focusing, and defocusing localized in the lithosphere beneath the source and receiver sites.

Identification of multiple underground explosions using the relative amplitude method

1988 ◽  
Vol 78 (2) ◽  
pp. 885-897
Author(s):  
R. A. Clark ◽  
R. G. Pearce
Keyword(s):  
Body Wave ◽  
The Body ◽  
P Wave ◽  
Relative Amplitude ◽  
Time Data ◽  
Large Measure ◽  
Source Discrimination ◽  
Nuclear Explosions ◽  
Short Period ◽  
Wave Forms

Abstract The relative amplitude method is applied to the few available good quality teleseismic P-wave seismograms from five presumed double nuclear explosions and one known multiple chemical explosion, under the “naive” assumption that the observed multiple arrivals correspond to P, pP, and sP from a single earthquake—an interpretation which is indeed consistent with the body-wave arrival time data in most cases. The purpose is to investigate the ability of relative amplitudes to identify correctly such multiple events for which established discrimination criteria may give earthquake-like or ambiguous results. For five of the examples, observed relative amplitudes from only four azimuthally well-distributed array seismograms are sufficient to exclude the single-earthquake interpretation. Deliberate attempts to simulate earthquake teleseismic P wave-forms using multiple explosions are restricted to simulation studies, and one of these is analyzed here using the same approach. We conclude that relative amplitudes can act as a valuable aid to source discrimination in cases where complexity gives rise to fallibility of conventional discriminants, even where only a small number of well-distributed teleseismic short-period array seismograms are available, their signal-to-noise ratios being maximized by suitable array design and careful choice of array site. The network need not be dense, since closely spaced observations of the focal sphere generally embody a large measure of redundancy.

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