Worldwide variations in the attenuative properties of the upper mantle as determined from spectral studies of short-period body waves

Der, Zoltan A.; Rivers, W.D.; McElfresh, T.W.; O’Donnell, Anne E.; Klouda, P.; Marshall, Mark D.

doi:10.1016/0031-9201(82)90124-8

Cited by 38 publications

(21 citation statements)

References 32 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: 82%

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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: 82%

“…The large variations in the mantle-averaged Q values imply much larger proportional changes in the upper-mantle Q in this layer. This means that the lateral Q differentials in the long-period band are just as pronounced as in the short-period band (Der et al 1982).…”

Section: Discussionmentioning

confidence: 96%

Attenuation of multiple ScS in various parts of the world

Chan

Der

1988

Geophysical Journal International

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“…The bands vary with depth (ANDERSON and GIVEN, 1982) and correlate with tectonic structures McELFRESH, 1976, 1980;DER et al, 1986). Across a broad range of surface-and body-wave frequencies from *0.01 to *100 Hz (e.g., DER et al, 1982DER et al, , 1986LEES et al, 1986;ABERCROMBIE, 1998), Q values consistently increase with frequency in a vast majority of observations. However, attenuation is also always measured indirectly and in the background of strong amplitude variations, and the difficulty of differentiating its apparent attributes from the true in situ properties is well known (DER and LEES, 1985;WHITE, 1992).…”

Section: Introductionmentioning

confidence: 84%

On the Causes of Frequency-Dependent Apparent Seismological Q

Morozov

2010

Pure Appl. Geophys.

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Variability of the Earth's structure makes a firstorder impact on attenuation measurements which often does not receive adequate attention. Geometrical spreading (GS) can be used as a simple measure of the effects of such structure. The traditional simplified GS compensation is insufficiently accurate for attenuation measurements, and the residual GS appears as biases in both Q 0 and g parameters in the frequency-dependent attenuation law Q(f) = Q 0 f g . A new interpretation approach bypassing Q(f) and using the attenuation coefficient v(f) = c ? pf/Q e (f) resolves this problem by directly measuring the residual GS, denoted c, and effective attenuation, Q e . The approach is illustrated by re-interpreting several published datasets, including nuclear-explosion and local-earthquake codas, Pn, and synthetic 50-300-s surface waves. Some of these examples were key to establishing the Q(f) concept.In all examples considered, v(f) shows a linear dependence on the frequency, c = 0, and Q e can be considered frequency-independent. Short-period crustal body waves are characterized by positive c SP values of (0.6-2.0) 9 10 -2 s -1 interpreted as related to the downward upper-crustal reflectivity. Long-period surface waves show negative c LP & -1.9 9 10 -5 s -1 , which could be caused by insufficient modeling accuracy at long periods. The above c values also provide a simple explanation for the absorption band observed within the Earth. The band is interpreted as apparent and formed by levels of Q e & 1,100 within the crust decreasing to Q e & 120 within the uppermost mantle, with frequencies of its flanks corresponding to c LP and c SP . Therefore, the observed absorption band could be purely geometrical in nature, and relaxation or scattering models may not be necessary for explaining the observed apparent Q(f). Linearity of the attenuation coefficient suggests that at all periods, the attenuation of both Rayleigh and Love waves should be principally accumulated at the sub-crustal depths (*38-100 km).

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“…Observations, as well as very general theoretical considerations, suggest that the quality factors and body wavespeeds are frequency dependent, but several aspects of dispersion are still controversial issues (DUREK and EKSTRÖ M 1997;ABERCROMBIE 1998;ROMANOWICZ 1998;WARREN and SHEARER 2002;FORD et al 2010;MOROZOV 2010MOROZOV , 2011XIE 2010). The debate hinges on the magnitude, and spatial as well as frequential variability (DER et al 1982;DREGER et al 2008;YOSHIMOTO and OKADA 2009) of attenuation, with it being generally accepted (WARREN and SHEARER 2002;YOSHIMOTO and OKADA 2009) that attenuation is: (a) intrinsic (due to conversion of wave energy into heat within the materials of the Earth), (b) due to scattering (a spatial redistribution of wavelike energy resulting from small-scale heterogeneity of the medium traversed by the seismic wave), and (c) linked to geometrical spreading of the wavefront emerging from the seismic source. More specifically, even if one accepts this vision [which has recently been enlarged to include 'fluctuation' attenuation (MOROZOV and BA-HARVAND AHMADI 2015)] of these types of attenuation, how can he accurately measure them and how to describe mathematically their relation to what is observed?…”

Section: Introductionmentioning

confidence: 99%

Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval

Wirgin

2016

Pure Appl. Geophys.

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The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.

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Worldwide variations in the attenuative properties of the upper mantle as determined from spectral studies of short-period body waves

Cited by 38 publications

References 32 publications

Attenuation of multiple ScS in various parts of the world

Attenuation of multiple ScS in various parts of the world

On the Causes of Frequency-Dependent Apparent Seismological Q

Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval

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