Frequency dependence of Q in the mantle underlying the shield areas of Eurasia, Part I: analyses of long period data

Der, Zoltan A.; Lees, Alison C.; Cormier, Vernon F.; Anderson, Lisa M.

doi:10.1111/j.1365-246x.1986.tb01983.x

Cited by 16 publications

(11 citation statements)

References 25 publications

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“…Compared in the same table are short period results obtained for P-wave spectral shapes cited from various studies (e.g. Der & Lees 1985;Der & McElfresh 1977;Der et al , 1986). The regional variation in the long-and short-period bands assume a similar pattern to long-period ScS results where the t* is higher in the tectonically active regions and lower in the more stable shield regions.…”

Section: Discussionmentioning

confidence: 84%

Attenuation of multiple ScS in various parts of the world

Chan

Der

1988

Geophysical Journal International

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A waveform and amplitude matching scheme is used to study regional variations of Qscs at low-frequency band between 0.02 and 0.1 Hz for paths across various parts of the world. The scheme estimates attenuation by convolving the first well-recorded, clear SCS, phase with multiples of trial t* operators until the phases so derived match the amplitude decay-rates and waveform characteristics of the observed later multiples.Thirty-five intermediate-to-deep focus earthquakes recorded at seismographic stations throughout the world were used in this study. The regions sampled are the tectonic and shield areas of Eurasia, tectonic regions of North America, shield regions of South America, and tectonic portions of NW, SW and E Pacific Ocean. In general, the regional differentials in t* between successive multiples of ScS are similar to those reported in earlier studies (Nakanishi 1979; Spikin & Jordan 1980). For the tectonic regions of Eurasia, tgcs are 5.0 f 1.1 s for a double passage through the mantle, whereas for the shield areas, they are around 2.8 f 0.4 s. For the tectonic regions of North America, our estimates of t& are 4.8 f 1.6 s. A mean t& of 6.3 f 0.9 s has been obtained for paths across the E Pacific while the N W and SE Pacific are characterized by moderate attenuation with average t& values of 4.4 f 0.7 and 4.2 f 0.8 s respectively. For central South America, the estimated tics is 2.7 f 0.7 s. Assuming that the lateral variations in Q observed using the ScS data are confined to a 200-300 km thick layer in the upper mantle, where the lateral velocity variations are also the most pronounced, these results imply lateral variations in shear wave Q of about an order of magnitude. The lateral variations of mantle Q in the upper mantle derived from these analyses of long-period ScS phases correlate well with mantle Q estimates from short period data. It is therefore unlikely that Q ( f ) appropriate to various types of upper-mantle structures converge at low frequencies of 0.02 to 0.1 Hz as required by the 'absorption-band shift' models.

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Section: Discussionmentioning

confidence: 84%

Attenuation of multiple ScS in various parts of the world

Chan

Der

1988

Geophysical Journal International

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“…The shear loss mechanism of attenuation translates into the approximate relationship t* s = 4 t* p when the typical mantle velocities for P and S waves are considered. The approximate validity of the relationship between shear wave and P-wave attenuation makes it possible to merge and jointly interpret P-and S-wave atenuation measurements (DER et al, 1986a;LEES et al, 1986) and thus make use of the greater sensitivity of S waves to build attenuation models (DER et al, 1986b).…”

Section: Teleseismic Energy Loss In the Short-period Bandmentioning

confidence: 99%

“…Thus the function t*( f ) must be constructed for each path by piecing together various types of information consisting of spectral ratios between assumed source spectra and absolute Q estimates derived from source independent amplitude decay measurements. Additional constraints may be provided from S-wave measurements, making the assumption that most losses occur in shear deformation (DER and LEES, 1985;DER et al, 1986a).…”

Section: Figurementioning

confidence: 99%

High-frequency

Der

1998

Pure appl. geophys.

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Investigations of the spectral characteristics of teleseismic body waves revealed that the spectral falloff rate between 1 Hz and 10 Hz is primarily controlled by anelastic attenuation along the path. In addition, the amount of high-frequency energy in teleseismic body waves is far above the level expected on the basis of Q estimates at low frequencies, thus leading to the idea of frequency dependence in Q. Q variations in the earth's mantle can be investigated by mapping out the variations of high frequency (4-10 Hz) energy relative to the low frequency (1 -3 Hz) energy in teleseismic P waves, and similar ratios at lower frequencies in teleseismic S waves. Because of the extreme sensitivity of spectral content of short-period body waves to Q variations, large uncertainties in other factors affecting spectral content can be tolerated in such studies. With the increasing number and density of broadband seismic stations recording at high sampling rates, tomographic studies of Q at high frequencies become possible.

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“…Surface-wave studies allow observations of regional variations of the crustal and mantle attenuation down to about 400 km (e.g., PATTON, 1980;MITCHELL, 1995). However, short-period, body-wave attenuation measurements still remain very limited (DER et al, 1986a). Global attenuation models are dominated by oceanic areas, whereas mantle attenuation shows a wide range of regional variations, as well as with depth and frequency (e.g., MITCHELL, 1995;DER et al, 1986b).…”

Section: Introductionmentioning

confidence: 99%

2-D Image of Seismic Attenuation beneath the Deep Seismic Sounding Profile "Quartz," Russia

Morozov

Морозова

Smithson

et al. 1998

Pure and Applied Geophysics

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We present a 2-D image of the upper mantle attenuation using nuclear explosion data from the ultra-long refraction/reflection profile ''Quartz.'' Our analysis is based on a modified common spectrum technique followed by least-squares inversion for Q and iterative ray tracing in the velocity structure obtained earlier. The resulting attenuation structure corroborates the earlier model for northern Eurasia, as well as our recent estimate based on the analysis of the long-range P n phase, and provides significantly more detail than the existing models. The resulting upper mantle attenuation structure is characterised by Q values ranging from 400 to 1800. Down to the depths of 150-190, and probably 400 km, the attenuation increases horizontally in SE direction, away from the Baltic Shield. Our model exhibits strong 2-D, vertical and horizontal attenuation contrasts. A high-attenuation layer in the depth range of 120-150 to 160-180 km can apparently be associated with the presence of a partial melts within the base of the lithosphere.

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Frequency dependence of Q in the mantle underlying the shield areas of Eurasia, Part I: analyses of long period data

Cited by 16 publications

References 25 publications

Attenuation of multiple ScS in various parts of the world

Attenuation of multiple ScS in various parts of the world

High-frequency

2-D Image of Seismic Attenuation beneath the Deep Seismic Sounding Profile "Quartz," Russia

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