Comparison of least squares analyses of long and short period P wave amplitudes

Willey, G.; Cleary, John; Marshall, Peter

doi:10.1111/j.1365-246x.1970.tb06057.x

Cited by 10 publications

(5 citation statements)

References 10 publications

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“…The way in which the P-wave amplitude decays beyond 90" is determined partly by the spectrum of the P-wave; low frequencies are diffracted preferentially around the mantlecore boundary so low-frequency P-waves appear to decay less rapidly beyond 90" than hghfrequency P-waves. This effect was clearly observed by Willey, Cleary & Marshall (1970) and Booth et at. (1974); a theoretical discussion of the frequency dependence of P-wave propagation around the core is given by Phinney & Cathles (1969).…”

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confidence: 67%

An analysis of P-wave amplitudes recorded by seismological stations in the USSR

Marshall¹,

Bingham

Young³

1986

Geophysical Journal International

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Short period P-wave amplitudes at Soviet seismic stations are analysed to determine an amplitude-distance curve in the range 0"-180" from the USSR. Station amplitude terms, corrected for crustal amplification effects, are determined from seismic sources located between 30" and 90". A relationship between these station terms and regional P, wave speed and regional heat flow is determined and is found to be in close agreement with similar observations in North America. Station amplitude terms were found to be reasonably uniform across the continental portion of the USSR but the Baikal Rift valley is characterized by very low P-wave amplitudes and is the most significant feature discernible from the P-wave amplitude terms.

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supporting

confidence: 67%

An analysis of P-wave amplitudes recorded by seismological stations in the USSR

Marshall¹,

Bingham

Young³

1986

Geophysical Journal International

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“…For waves scattered from any small volume element S V in or near the crust, the effect of focusing or defocusing by the Earth's velocity structure would be similar to that for direct waves originating within SV. The amplitudes of direct P-wave first arrivals are virtually independent of distance from 30" to 80" (Cleary 1967;Willey, Cleary & Marshall 1970). It follows that for scattering distances in this range, the relative scattered wave amplitudes would not be significantly dependent on the focusing factor.…”

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confidence: 87%

P-Wave Scattering in the Earth's Crust and Upper Mantle

1975

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The codas which follow P-phase onsets on seismic records can be interpreted in terms of waves scattered from random inhomogeneities in the Earth's crust and upper mantle. In particular, the so-called precursors to PP have travel times and slownesses consistent with the interpretation of these signals as waves scattered from direct P-waves incident at the Earth's surface at distances greater than about 20" from either the source or receiver. Significant differences between recordings at the Warramunga array of PP precursors from two Novaya Zemlya explosions are extremely difficult to account for on any interpretation previously suggested, but are fully consistent with the random variations to be expected on the proposed scattering mechanism.The present interpretation accounts for the major observed features of P codas, including their durations and the variations in slowness along the trains. Precursors to P'P' can also be interpreted as scattering phenomena. Thus the interpretation removes the need to postulate sharp reflecting discontinuities in the uppermost few hundred kilometres of the upper mantle.

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“…For this reason in this analysis the LP and SP amplitudes are analysed separately. Willey, Cleary & Marshall (1970) have made some comparisons of LP and SP P amplitudes but the LP and SP observations they use are from different groups of earthquakes and few stations are common to both LP and SP analyses so a full comparison at the two periods is not possible. In this paper however we only use data from stations that have recorded both LP and SP signals from a given earthquake so that a LP and SP recording is obtained for every source-receiver path.…”

Section: Logo(a/t) = F?lb-b(a)-smentioning

confidence: 99%

Long and Short Period P-wave amplitudes from Earthquakes in the Range 0 -114

Booth

Marshall²,

Young³

1974

Geophysical Journal International

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Long period (16 s) and short period (1 s) P-wave amplitudes from shallow earthquakes recorded in the distance range 0"-114" are analysed to separate the effects of earthquake size, epicentral distance and station structure. The LP and SP vertical component amplitudes are analysed separately so that any period dependent effects can be determined.The results show that distance effects on both LP and SP amplitudes are significant when the whole range 0-114" is considered but between about 30" and 90" the distance effects are not significant. Further the distance effects do depend on period in the range 0-114" but again between 30" and 90" the distance effects are independent of period. In determining magnitude then a single constant correction for distance can be applied to both LP and SP recordings in the range 30"-90". Outside this range the correction depends on both distance and period.Station effects are significant for both the LP and SP analyses with little correlation between the LP and SP effects for individual stations. The SP effects can be attributed to variations in Q in the upper mantle; stations recording below average amplitude being underlain by lower Q than those recording amplitudes above average. The SP effects for a particular station will thus also be source effects for shallow events with epicentres near the station. The value of applying corrections for such source effects to magnitude estimates is demonstrated using data from two explosions of the same yield fired at two widely different test sites. Without corrections for source effects the magnitudes differ by 0.6 units, with source effects the difference is 0.02 units.The LP station effects are more difficult to interpret, but for one group of stations on the coastal plains of the Gulf of Mexico and Eastern USA which show large positive effects (above average amplitudes) it is demonstrated by modelling that these effects could be explained by the amplification effects of the large thicknesses of sediment underlying the stations.Comparing the estimates of magnitude (earthquake size) obtained from the LP and SP analyses shows that on average the LP and SP magnitudes are equal but correlation of LP and SP magnitudes for individual earthquakes is poor. This lack of correlation may simply be due to lack of data since only a small number of readings (1-4) contribute to each magnitude estimate, but this needs further study.

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Comparison of least squares analyses of long and short period P wave amplitudes

Cited by 10 publications

References 10 publications

An analysis of P-wave amplitudes recorded by seismological stations in the USSR

An analysis of P-wave amplitudes recorded by seismological stations in the USSR

P-Wave Scattering in the Earth's Crust and Upper Mantle

Long and Short Period P-wave amplitudes from Earthquakes in the Range 0 -114

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