Study of teleseismic P II - amplitude data

Evernden, Jack F.; Clark, Don M

doi:10.1016/0031-9201(70)90026-9

Cited by 33 publications

(19 citation statements)

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“…This has been confirmed in several studies of magnitude variations across the US (Evernden & Clark 1970;Cleary 1967;North 1977;Booth, Marshall & Young 1974;Butler & Ruff 1980). All the various studies show a negative bias in amplitudes in most of the WUS relative to the EUS as a whole even though the methods of data selection and amplitude measurement vary, and the reported bias values for common stations also differ considerably.…”

Section: P -W a V E Amplitude Anomaliessupporting

confidence: 56%

An investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the United States in the 0.5-4 Hz band

Der

McElfresh

O’Donnell

1982

Geophysical Journal International

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Studies of teleseismic Pand S-wave amplitudes and spectra in the 0.5-4 Hz band show large variations in the attenuative properties of the upper mantle under the United States. The data indicate that attenuation is greatest under the south-western United States including, but not confined to, the Basin and Range province. The lowest attenuation prevails under the north central shield regions. The north-eastern part of the country, consisting of New England and possibly including a larger area along the eastern seaboard, is characterized by moderate attenuation in the mantle.The level of the high-frequency energy in short-period seismic waves and the differences between Q values derived from short-and long-period data indicate that Q is frequency dependent. The form of frequency dependence of t* compatible with the data in the 0.5-4 Hz range does not allow a rapid decrease of t * with increasing frequency. Rather it supports a gradual decrease covering the broader 0.1-4Hz range. The curves of t* versus frequency, for shield-to-shield and mixed shield-to-western United States type paths are parallel with an average difference of 0.2 s in t* in the short-period band, but may diverge towards the long-period band. For both curves t: is below 1 s. For shield-to-shield paths t: must be below 0.5 s at 1 Hz.

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Section: P -W a V E Amplitude Anomaliessupporting

confidence: 56%

An investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the United States in the 0.5-4 Hz band

Der

McElfresh

O’Donnell

1982

Geophysical Journal International

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“…The SP effects show the well-known pattern(Cleary 1967;Evernden & Clark 1970) of negative effects in the west of the continent and positive effects in the centre and east of the continent. Thus the recorded amplitudes are smaller in the west than in the east.…”

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confidence: 71%

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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“…In light of such findings, Butler's results are not substantially different from those of other studies, especially when the results are compared in the areas of common coverage (Cleary 1967;Evernden & Clark 1970;Booth, Marshall & Young 1974). However, larger magnitude differentials can be expected in some cases when very different tectonic regions are being compared, such as the Basin and Range region and the continental shield.…”

mentioning

confidence: 55%

Comments on 'P-wave amplitudes in the United States: east--west variations and variability', by Rhett Butler

Der¹

1985

Geophysical Journal International

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Study of teleseismic P II - amplitude data

Cited by 33 publications

References 1 publication

An investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the United States in the 0.5-4 Hz band

An investigation of the regional variations and frequency dependence of anelastic attenuation in the mantle under the United States in the 0.5-4 Hz band

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

Comments on 'P-wave amplitudes in the United States: east--west variations and variability', by Rhett Butler

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