The Instantaneous Amplitude, Phase and Frequency in Seismic Event Detection, Timing and Identification

Unger, Rudolf

doi:10.1007/978-94-009-8531-5_36

Cited by 3 publications

(1 citation statement)

References 3 publications

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“…The half-width was employed as a quantitative measure for the signal duration of a phase. It is defined as the separation time of the first and last arrival exceeding one-half of the maximum of the envelope function which can be calculated using the Hilbert transform (Unger 1981). An example of how the half-width was determined is given in Fig.…”

Section: U R a T I O Nmentioning

confidence: 99%

Short-period S-P conversion in the mantle at a depth near 700 km

Bock

1984

Geophysical Journal International

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Data from 16 deep earthquakes originating in the Tonga subduction zone and recorded at the Warramunga Seismic Array (WRA) in central Australia show the presence of a distinct later arrival in the coda of P.This phase which is not predicted by smooth velocity-depth models of the Earth has been called '*Y' in the paper. Slownesses and arrival azimuths o f X are similar to those of the P-wave. It is unlikely that X was radiated as the result of multiple focal activity because a corresponding phase was not observed, neither in the coda of ScP nor on seismograms of seismic stations located at close epicentral distances. Relative to P, the variation in arrival times with focal depth of the earthquakes indicates that S is produced by S-Pconversion below the source, at a depth near 700 km. Most of the observed X phases have approximately the same signal duration as the P-waves thus suggesting a transition zone near 700 km which is only a few kilometres thick. Synthetic seismograms calculated for a model with a first-order seismic discontinuity at a depth of 700km show reasonable agreement with the observations. As demonstrated by the synthetic seismogram modelling the amplitude of X depends on the radiation pattern of the earthquake source. Variations in the radiation pattern offer a plausible explanation that, first, X is only intermittently detected at WRA and, secondly, that X has most frequently been observed from the southern part of the Tonga subduction zone.

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Section: U R a T I O Nmentioning

confidence: 99%

Short-period S-P conversion in the mantle at a depth near 700 km

Bock

1984

Geophysical Journal International

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Seismic Active Monitoring System Concept

Unger

2010

Handbook of Geophysical Exploration: Seismic Exploration

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Maximum spectral energy for seismic magnitude estimation. Part I: Rayleigh-wave magnitude

Yacoub

1998

Bulletin of the Seismological Society of America

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A method for accurate estimation of surface-wave magnitudes is presented as an alternative to Ms, the classical time-domain magnitude. The salient features of the method are the use of velocity and frequency windows to isolate seismic phases and the use of maximum spectral energy to characterize ground motion for magnitude estimation. Rayleigh-wave ground motion estimated by the new method is generally consistent, but not identical, to that measured in the time domain. The estimated ground motion is used to determine Rayleigh-wave spectral magnitudes for 27 presumed nuclear explosions, from several test sites. These magnitudes are studied for their accuracy and for their transportability between nuclear explosion test sites. For accuracy, we compare spectral magnitudes MR with their corresponding time-domain-measured magnitudes Ms. The comparison encompasses network magnitudes and their standard deviations and magnitude residuals. For transportability, we studied the variations in mb (body-wave magnitude), Ms (time-domain magnitude), and MR (spectral magnitude) for network-averaged mb-equivalent presumed nuclear explosions at the Shagan River and the Qingger test sites. These studies showed that this spectral magnitude has a smaller error than classical time-domain Ms and that it is transportable between the two test sites.

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The Instantaneous Amplitude, Phase and Frequency in Seismic Event Detection, Timing and Identification

Cited by 3 publications

References 3 publications

Short-period S-P conversion in the mantle at a depth near 700 km

Short-period S-P conversion in the mantle at a depth near 700 km

Seismic Active Monitoring System Concept

Maximum spectral energy for seismic magnitude estimation. Part I: Rayleigh-wave magnitude

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