Complex P-Wave Seismograms from Simple Earthquake Sources

Douglas, A.; Young, J. B.; Hudson, John

doi:10.1111/j.1365-246x.1974.tb02448.x

Cited by 18 publications

(13 citation statements)

References 8 publications

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“…This shows that, in general, it is impossible to generate a complex coda of reasonable amplitude by a single thin heterogeneous layer, or even by single scattering. It has already been demonstrated (Douglas, Young & Hudson 1974) that complex horizontal layering will not produce a significantly complex signal, and it is expected that the combination of layering and single scattering will also fail. The main contenders for the generation of complex signals (apart from complex sources) Q 1997 RAS, GJI 128,[197][198][199][200][201][202][203] Scattering from a heterogeneous layer 203 are therefore multiple scattering, and a mechanism whereby the main P signal, but not the scattering, is drastically reduced in amplitude (Douglas, Hudson & Barby 1981), for instance by observations in the neighbourhood of a node of P radiation from the source.…”

Section: And Thenmentioning

confidence: 99%

Time-domain computation of scattering from a heterogeneous layer

Hudson

1997

Geophysical Journal International

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S U M M A R YAdopting Born and ray approximations, time-domain synthetic seismograms for P-P and P-S scattering from a plane wave incident on a thin, laterally heterogeneous layer are presented in this paper. The time-domain P coda is a convolution between a structure function and the second-order derivative of the time function of the incident P wave. Examples of synthetic seismograms are given using a time function from a computed short-period seismogram for a point explosive source in a half-space. These show that it is impossible, with realistic values of the parameters involved, to generate significant codas when only single scattering is involved.

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Section: And Thenmentioning

confidence: 99%

Time-domain computation of scattering from a heterogeneous layer

Hudson

1997

Geophysical Journal International

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“…Many studies of seismic signal complexity focused on examining the physical mechanisms behind simple and complex waveforms (e.g., DOUGLAS et al, 1973;1974;BARLEY, 1977;BOWERS, 1996). Typically shallow earthquakes present complex P-wave signatures relative to singlecharge explosions.…”

Section: Introductionmentioning

confidence: 99%

Rediscovering Signal Complexity as a Teleseismic Discriminant

Taylor

Anderson

2009

Pure appl. geophys.

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We re-examine the utility of teleseismic seismic complexity discriminants in a multivariate setting using United Kingdom array data. We measure a complexity discriminant taken on array beams by simply taking the logarithm of the ratio of the P-wave coda signal to that of the first arriving direct P wave (b CF ). The single station complexity discriminant shows marginal performance with shallow earthquakes having more complex signatures than those from explosions or deep earthquakes. Inclusion of secondary phases in the coda window can also degrade performance. However, performance improves markedly when two-station complexity discriminants are formed showing false alarm rates similar to those observed for network m b -M s . This suggests that multistation complexity discriminants may ameliorate some of the problems associated with m b -M s discrimination at lower magnitudes. Additionally, when complexity discriminants are combined with m b -M s there is a tendency for explosions, shallow earthquakes and deep earthquakes to form three distinct populations. Thus, complexity discriminants may follow a logic that is similar to m b -M s in terms of the separation of shallow earthquakes from nuclear explosions, although the underlying physics of the two discriminants is significantly different.

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“…(The term 'depth phase' denotes arrivals due to the reflection of energy at seismic discontinuities above a hypocentre.) Many shallow earthquakes (especially those beneath oceans) appear to produce P-wave seismograms of this type, probably because high-impedance contrasts due to shallow low-velocity layers are present (Douglas, Young & Hudson 1974). As an aid to interpretation, we compute seismograms using a model of the velocity structure above the hypocentre, and compare them with the observed seismograms.…”

Section: Introductionmentioning

confidence: 99%

A fault plane solution using theoretical P seismograms

Barley¹,

Pearce²

1977

Geophysical Journal International

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We use the method of Hudson and Douglas, Hudson & Blamey to compute seismograms which simulate the codas of 10 short period P-wave seismograms from a shallow earthquake. The polarities and relative amplitudes of P and pP measured from seven of the observed seismograms are used to compute a fault plane solution with confidence limits, assuming that the source radiates as a double couple. This solution is in approximate agreement with that given for the same earthquake by Sykes & Sbar, who used only the onset polarities of short-period P waves. The small difference between the two solutions can be explained by interference between the true first motion of P and microseismic noise at two stations.The results show that, for some shallow earthquakes, the relative amplitude method has the following advantages over the first motions method. First, a P/pP amplitude ratio (with appropriate confidence limits) can always be measured, even in seismograms which are so noisy that the first motion of P is uncertain. Second, the fault plane solutions obtained from relative amplitudes have known confidence limits. Finally, by using more information from each seismogram, the relative amplitude method requires considerably fewer seismograms than the first motions method.

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Complex P-Wave Seismograms from Simple Earthquake Sources

Cited by 18 publications

References 8 publications

Time-domain computation of scattering from a heterogeneous layer

Time-domain computation of scattering from a heterogeneous layer

Rediscovering Signal Complexity as a Teleseismic Discriminant

A fault plane solution using theoretical P seismograms

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