ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties (2005)

Stackhouse, Stephen ; Kendall, J-Michael ; Brodholt, John ; [et al.]

[s.l.] : Nature Publishing Group

Nature 438 (2005), S. 1004-1007

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] Constraining the chemical, rheological and electromagnetic properties of the lowermost mantle (D″) is important to understand the formation and dynamics of the Earth's mantle and core. To explain the origin of the variety of characteristics of this layer observed with seismology, a ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/nature04345

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2

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Effect of eight outer continental shelf drilling muds on the calcification rate and free amino acid pool of the coralAcropora cervicornis (1984)

Powell, E. N. ; Kendall, J. J. ; Connor, S. J. ; [et al.]

Springer

Bulletin of environmental contamination and toxicology 33 (1984), S. 362-372

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ISSN: 1432-0800

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01625556

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3

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Recovery by the coralAcropora cervicornis after drilling mud exposure. The free amino acid pool (1984)

Powell, E. N. ; Connor, S. J. ; Kendall, J. J. ; [et al.]

Springer

Archives of environmental contamination and toxicology 13 (1984), S. 243-258

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ISSN: 1432-0703

Source: Springer Online Journal Archives 1860-2000

Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine

Notes: Abstract Corals were exposed to drilling mud for 24 hr and then allowed to recover for 48 hr in clean seawater. Depending on the concentration and the mud used, exposure produced either an increase or decrease in free amino acid (FAA) pool size. Aspartate was affected to a greater degree than other amino acids. No clear instance of recovery could be ascertained after 48 hr in clean seawater. In several cases, corals, apparently unaffected by a 24 hr exposure, nevertheless suffered significant changes in the FAA pool during the 48 hr recovery period. Thus, the degree of toxicity of the drilling mud could not be accurately predicted from the 24 hr exposure data. In many cases, the choice of a normalizing parameter determined whether two sets of data were significantly different or not. Accurate effects assessment depends on a comparison of several methods of normalization to confirm statistical results.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01055883

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4

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Magma-assisted rifting in Ethiopia (2005)

Stuart, G. W. ; Ebinger, C. J. ; Bastow, I. D. ; [et al.]

[s.l.] : Macmillian Magazines Ltd.

Nature 433 (2005), S. 146-148

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The rifting of continents and evolution of ocean basins is a fundamental component of plate tectonics, yet the process of continental break-up remains controversial. Plate driving forces have been estimated to be as much as an order of magnitude smaller than those required to rupture thick ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/nature03161

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5

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The importance of monitoring metabolic recovery in the coral Acropora cervicornis after short-term exposure to drilling muds: Calcification rate and protein concentration (1984)

Kendall, J. J. ; Powell, E. N. ; Connor, S. J. ; [et al.]

Springer

Coral reefs 2 (1984), S. 215-225

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ISSN: 1432-0975

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract The effect of used drilling muds on coral health was examined by monitoring changes in calcification rate and soluble tissue protein concentration in the coral Acropora cervicornis. Exposure to 25 ppm (v/v) of one mud for 24 h reduced calcification rate in the growing tips by as much as 62%. In recovery experiments, corals were exposed to drilling muds for 24 h; some of them were allowed to recover in clean seawater for 48 h. After the 24-hour exposure, calcification rates were significantly less than those of the controls. After a 48-hour recovery period, calcification rates returned to control levels for one mud but were still significantly below control levels for another. The results indicate that the capacity for recovery after exposure cannot be predicted from the results of experiments on exposure only. Recovery capacity must be independently verified for all studies on the effects of short-term exposure to drilling muds.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00263575

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Petrofabric-derived seismic properties of a mylonitic quartz simple shear zone: implications for seismic reflection profiling (2007)

Lloyd, G. E. ; Kendall, J. M.

In: Geological Society Special Publication 240: 75-94.

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Publication Date: 2007-10-08

Description: The link between petrofabric (LPO) and seismic properties of an amphibolite-facies quartzo-feldspathic shear zone is explored using SEM/EBSD. The shear-zone LPO develops by a combination of slip systems and dauphine twinning, with a-maximum parallel to lineation (X) and c-maximum normal to mylonitic foliation (XY). The LPO are used to predict elastic parameters, from which the three-dimensional seismic properties of different shear-zone regions are derived. Results suggest that LPO evolution is reflected in the seismic properties but the precise impact is not simple. In general, the P-wave velocity (VP) minimum is parallel to the a-axis maximum; the direction of maximum shear-wave splitting (AVS) is parallel to mylonitic foliation; and the VP maximum and AVS minimum are parallel to the c-axis maximum. The seismic anisotropy predicted is significant and increases from shear zone wallrock to mature mylonite. The P-wave anisotropy ranges from 11 to 13%, fast and slow shear waves' anisotropies range from 6 to 15% and the magnitude of shear-wave splitting ranges from 9 to 16%. Nevertheless, such anisotropy requires a considerable thickness of rock with this LPO before it becomes seismically visible (i.e. 100s of m for local earthquakes; 10s of m for controlled source experiments). However, reflections and mode conversions provide much better resolution, particularly across tectonic boundaries. The low symmetry and strong anisotropy due to the LPO suggest that multi-azimuth wide-angle reflection data may be useful in the determination of the deformation characteristics of deep shear zones.

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Mantle upwellings, melt migration and the rifting of Africa: insights from seismic anisotropy (2007)

Kendall, J.-M. ; Pilidou, S. ; Keir, D. ; [et al.]

In: Geological Society Special Publication 259: 55-72.

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Publication Date: 2007-10-08

Description: The rifting of continents and eventual formation of ocean basins is a fundamental component of plate tectonics, yet the mechanism for break-up is poorly understood. The East African Rift System (EARS) is an ideal place to study this process as it captures the initiation of a rift in the south through to incipient oceanic spreading in north-eastern Ethiopia. Measurements of seismic anisotropy can be used to test models of rifting. Here we summarize observations of anisotropy beneath the EARS from local and teleseismic body-waves and azimuthal variations in surface-wave velocities. Special attention is given to the Ethiopian part of the rift where the recent EAGLE project has provided a detailed image of anisotropy in the portion of the Ethiopian Rift that spans the transition from continental rifting to incipient oceanic spreading. Analyses of regional surface-waves show sub-lithospheric fast shear-waves coherently oriented in a north-eastward direction from southern Kenya to the Red Sea. This parallels the trend of the deeper African superplume, which originates at the core-mantle boundary beneath southern Africa and rises towards the base of the lithosphere beneath Afar. The pattern of shear-wave anisotropy is more variable above depths of 150 km. Analyses of splitting in teleseismic phases (SKS) and local shear-waves within the rift valley consistently show rift-parallel orientations. The magnitude of the splitting correlates with the degree of magmatism and the polarizations of the shear-waves align with magmatic segmentation along the rift valley. Analysis of surface-wave propagation across the rift valley confirms that anisotropy in the uppermost 75 km is primarily due to melt alignment. Away from the rift valley, the anisotropy agrees reasonably well within the pre-existing Pan-African lithospheric fabric. An exception is the region beneath the Ethiopian plateau, where the anisotropy is variable and may correspond to pre-existing fabric and ongoing melt-migration processes. These observations support models of magma-assisted rifting, rather than those of simple mechanical stretching. Upwellings, which most probably originate from the larger superplume, thermally erode the lithosphere along sites of pre-existing weaknesses or topographic highs. Decompression leads to magmatism and dyke injection that weakens the lithosphere enough for rifting and the strain appears to be localized to plate boundaries, rather than wider zones of deformation.

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Seismic anisotropy as an indicator of reservoir quality in siliciclastic rocks (2008)

Kendall, J.-M. ; Fisher, Q. J. ; Crump, S. Covey ; [et al.]

In: Geological Society Special Publication 292: 123-136.

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Publication Date: 2008-01-02

Description: Improving the accuracy of subsurface imaging is commonly the main incentive for including the effects of anisotropy in seismic processing. However, the anisotropy itself holds valuable information about rock properties and, as such, can be viewed as a seismic attribute. Here we summarize results from an integrated project that explored the potential to use observations of seismic anisotropy to interpret lithological and fluid properties (the SAIL project). Our approach links detailed petrofabric analyses of reservoir rocks, laboratory based measurements of ultrasonic velocities in core samples, and reservoir-scale seismic observations. We present results for the Clair field, a CarboniferousDevonian reservoir offshore Scotland, west of the Shetland Islands. The reservoir rocks are sandstones that are variable in composition and exhibit anisotropy on three length-scales: the crystal, grain and fracture scale. We have developed a methodology for assessing crystal-preferred-orientation (CPO) using a combination of electron back-scattered diffraction (EBSD), X-ray texture goniometry (XRTG) and image analysis. Modal proportions of individual minerals are measured using quantitative X-ray diffraction (QXRD). These measurements are used to calculate the intrinsic anisotropy due to CPO via Voigt-Reuss-Hill averaging of individual crystal elasticities and their orientations. The intrinsic anisotropy of the rock is controlled by the phyllosilicate content and to a lesser degree the orientation of quartz and feldspar; the latter can serve as a palaeoflow indicator. Our results show remarkable consistency in CPO throughout the reservoir and allow us to construct a mathematical model of reservoir anisotropy. A comparison of CPO-predicted velocities and those derived from laboratory measurements of ultrasonic signals allows the estimation of additional elastic compliance terms due to grain-boundary interactions. The results show that the CPO estimates are good proxies for the intrinsic anisotropy of the clean sandstones. The more micaceous rocks exhibit enhanced anisotropy due to interactions between the phyllosilicate grains. We then compare the lab-scale predictions with reservoir-scale measurements of seismic anisotropy, based on amplitude variation with offset and azimuth (AVOA) analysis and non-hyperbolic moveout. Our mathematical model provides a foundation for interpreting the reservoir-scale seismic data and improving the geological modelling of complex reservoirs. The observed increases in AVOA signal with depth can only be explained with an increase in fracturing beneath the major unit boundaries, rather than a change in intrinsic CPO properties. In general, the style and magnitude of anisotropy in the Clair field appears to be indicative of reservoir quality.

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