A comparison of the anelasticity structure beneath western South America and Japan

Sacks, I. Selwyn; Okada, Hiroo

doi:10.1016/0031-9201(74)90139-3

Cited by 73 publications

(21 citation statements)

References 10 publications

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“…We used an S-wave atenuation structure for the upper mantle beneath Japan (Okada 1977). This mantle Qs is in accord with that of other studies (Anderson, Ben-Menahem & Archambeau 1965;Sacks & Okada 1974;Choy & Cormier 1986;Bowman 1988 Figure 14 shows the ray paths for MAT and SHK. We computed t* for both phases beginning at a depth of 450 km.…”

Section: Attenuationsupporting

confidence: 92%

Study of the structure of the slab-mantle interface using reflected and converted seismic waves

Helffrich

Stein

1993

Geophysical Journal International

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Seismic waves reflected and converted at the interface between a downgoing slab and the mantle above it can provide important constraints on the velocity contrast at the interface and hence on the properties of the downgoing lithosphere. Modelling studies suggest that different physical mechanisms may contribute to the velocity contrast at different depths along the interface. To explore the possible mechanisms, we examine the amplitudes of seismic waves reflected and converted at the slab-mantle interface in Japanese subduction zones. Slab-face P-reflection amplitudes suggest a velocity contrast ranging upwards to -10 per cent at depths of between 300 and 400 km. PIS amplitude ratios from ScS-to-P conversions at the slab-mantle interface depend on the depth of conversion and are large, 0.14 and 0.12, at stations SHK and MAT.The size of the velocity contrasts and amplitude ratios suggests that a model of the interface more complicated than one involving merely temperature and/or compositional effects is required. We use these observations to constrain layered models of the slab-mantle interface using Thomson-Haskell matrix modelling, comparing observations with calculated amplitude ratios. The results suggest that the crustal layer of basaltic composition, persisting to depth during subduction, plays a role in the generation of the shallow converted waves. The deeper conversions appear t o require layering as well, perhaps involving eclogite at the slab surface in addition t o oriented olivine in the overlying mantle and the a-p (and a-y) phase transformations in olivine within the slab.

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Section: Attenuationsupporting

confidence: 92%

Study of the structure of the slab-mantle interface using reflected and converted seismic waves

Helffrich

Stein

1993

Geophysical Journal International

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“…The east side of the circum-Pacific belt is considered to be a more structurally stable massif than the west side, which is considered as a multibranch area, as it was supported by the results of previous studies (KARIG, 1971;MOLNAR and OLIVER, 1969;SACKS and OKADA, 1975;TSAPANOS, 1990). The present study contributes to previous results by examining the parameter of the Gumbel's third asymptotic distribution of extreme values.…”

Section: Discussionsupporting

confidence: 75%

Regional Variation of the ω Values in the Circum-Pacific Belt

Tsapanos

1997

Pure appl. geophys.

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A data set of earthquakes which occurred in the circum-Pacific regions has been used to compute the values. This parameter is obtained through Gumbel's third asymptotic distribution of extreme values and is well known as upper bound magnitude. The results show relatively higher values in South America, Central America and Mexico, than in the western part of the circum-Pacific belt. The results are interpreted in terms of the different mechanical structure (heterogeneity) of the materials in the eastern and western parts of the examined area.

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“…Unfortunately, there are no studies of ScS that could be clearly associated with purely shield type paths and none under the eastern United States. Nevertheless, the average Qscs values of 600 for the whole mantle by Kovach & Anderson (1964) and 580 by Sat0 & Espinosa (1 967) may be indicative of Q values in regions above the downgoing slab in South America that may have Q characteristics similar to shields (Sacks & Okada 1974). These Q values are considerably higher than those obtained from multiple ScS studies elsewhere (Sipkin & Jordan 1980), but the corresponding t: at teleseismic distances in such structures would still be 0.4-0.5 s, twice the $ from spectral ratios in the short-period band along similar paths.…”

Section: Z a Der T W Mcelfresh And A O'donnellmentioning

confidence: 99%

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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A comparison of the anelasticity structure beneath western South America and Japan

Cited by 73 publications

References 10 publications

Study of the structure of the slab-mantle interface using reflected and converted seismic waves

Study of the structure of the slab-mantle interface using reflected and converted seismic waves

Regional Variation of the ω Values in the Circum-Pacific Belt

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

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