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Shear wave statics using receiver functions 总被引：1，自引：0，他引：1
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David W. Podlesak Ann-Marie Torregrossa M. Denise Dearing Thure E. Cerling 《Geochimica et cosmochimica acta》2008,72(1):19-35
Oxygen and hydrogen isotope signatures of animal tissues are strongly correlated with the isotope signature of local precipitation and as a result, isotope signatures of tissues are commonly used to study resource utilization and migration in animals and to reconstruct climate. To better understand the mechanisms behind these correlations, we manipulated the isotope composition of the drinking water and food supplied to captive woodrats to quantify the relationships between drinking water (δdw), body water (δbw), and tissue (δt). Woodrats were fed an isotopically constant food but were supplied with isotopically depleted or enriched water. Some animals were switched between these waters, allowing simultaneous determination of body water turnover, isotope change recorded in teeth and hair, and fractional contributions of atmospheric O2, drinking water, and food to the oxygen and hydrogen budgets of the animals. The half-life of the body water turnover was 3-6 days. A mass balance model estimated that drinking water, atmospheric O2, and food were responsible for 56%, 30%, and 15% of the oxygen in the body water, respectively. Drinking water and food were responsible for 71% and 29% of the hydrogen in the body water, respectively. Published generalized models for lab rats and humans accurately estimated δbw, as did an updated version of a specific model for woodrats. The change in drinking water was clearly recorded in hair and tooth enamel, and multiple-pool and tooth enamel forward models closely predicted these changes in hair and enamel, respectively. Oxygen and hydrogen atoms in the drinking water strongly influence the composition of the body water and tissues such as hair and tooth enamel; however, food and atmospheric O2 also contribute oxygen and/or hydrogen atoms to tissue. Controlled experiments allow researchers to validate models that estimate δt based on δdw and so will increase the reliability of estimates of resource utilization and climate reconstruction. 相似文献
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A modified Lax-Wendroff correction for wave propagation in attenuating and dispersive media described by Zener elements is presented. As opposed to the full correction, this new technique is explicit and offers large computational savings. The technique may be applied to a wide variety of hyperbolic problems. Here, the concept is illustrated for wave propagation in visco-acoustic media. 相似文献
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Caroline van Breukelen Chris Simpson Steve Rawlings Masayuki Akiyama David Bonfield Lee Clewley Matt J. Jarvis Tom Mauch Tony Readhead Ann-Marie Stobbart Mark Swinbank Mike Watson 《Monthly notices of the Royal Astronomical Society》2009,395(1):11-27
We discuss the optical properties, X-ray detections and active galactic nucleus (AGN) populations of four clusters at z ∼ 1 in the Subaru–XMM Deep Field (SXDF). The velocity distribution and plausible extended X-ray detections are examined, as well as the number of X-ray point sources and radio sources associated with the clusters. We find that the two clusters that appear virialized and have an extended X-ray detection contain few, if any, AGN, whereas the two pre-virialized clusters have a large AGN population. This constitutes evidence that the AGN fraction in clusters is linked to the clusters' evolutionary stage. The number of X-ray AGN in the pre-virialized clusters is consistent with an overdensity of a factor of ∼200; the radio AGN appear to be clustered with a factor of 3 to 6 higher. The median K -band luminosities of LK = 1.7 ± 0.7 L * for the X-ray sources and LK = 2.3 ± 0.1 L * for the radio sources support the theory that these AGN are triggered by galaxy interaction and merging events in sub-groups with low internal velocity distributions, which make up the cluster environment in a pre-virialization evolutionary stage. 相似文献
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Johan O. A. Robertsson Robert Laws Chris Chapman Jean-Pierre Vilotte Elise Delavaud 《Geophysical Journal International》2006,167(1):70-76
We compare three numerical methods to model the sea surface interaction in a marine seismic reflection experiment (the frequencies considered are in the band 10–100 Hz): the finite-difference method (FDM), the spectral element method (SEM) and the Kirchhoff method (KM). A plane wave is incident at angles of 0° and 30° with respect to the vertical on a rough Pierson–Moskowitz surface with 2 m significant wave height and the response is synthesized at 6, 10 and 50 m below the average height of the sea surface. All three methods display an excellent agreement for the main reflected arrival. The FDM and SEM also agree very well all through the scattered coda. The KM shows some discrepancies, particularly in terms of amplitudes. 相似文献
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Jens Wittsten Fredrik Andersson Johan Robertsson Lasse Amundsen 《Geophysical Prospecting》2019,67(6):1486-1497
A major focus of research in the seismic industry of the past two decades has been the acquisition and subsequent separation of seismic data using multiple sources fired simultaneously. The recently introduced method of signal apparition provides a new take on the problem by replacing the random time-shifts usually employed to encode the different sources by fully deterministic periodic time-shifts. In this paper, we give a mathematical proof showing that the signal apparition method results in optimally large regions in the frequency–wavenumber space where exact separation of sources is achieved. These regions are diamond shaped and we prove that using any other method of source encoding results in strictly smaller regions of exact separation. The results are valid for arbitrary number of sources. Numerical examples for different number of sources (three, respectively, four sources) demonstrate the exact recovery of these diamond-shaped regions. The implementation of the theoretical proofs in the field is illustrated by the results of a conducted field test. 相似文献
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Constantin Mildner Filippo Broggini Carlos Alberto da Costa Filho Johan O.A. Robertsson 《Geophysical Prospecting》2019,67(8):2085-2103
Imaging a target zone below a salt body can be challenging because large velocity contrasts in the overburden between the salt and surrounding sediments generate internal multiples, which interfere with primary reflections from the target level in the imaging process. This can lead to an erroneous interpretation of reflections in the sub-salt area if multiples are misinterpreted as primaries. The Marchenko redatuming method may enable imaging of the sub-salt target area where the effect of the multiply-scattering overburden is removed. This is achieved by creating a redatumed reflection response where virtual sources and receivers are located below the overburden using a macromodel of the velocity field and the surface reflection data. The accuracy of the redatumed data and the associated internal multiple removal, however, depends on the accurate knowledge of the source wavelet of the acquired reflection data. For the first time, we propose a method which can accurately and reliably correct the amplitudes of the reflection response in field data as required by the Marchenko method. Our method operates by iteratively and automatically updating the source function so as to cancel the most artefact energy in the focusing functions, which are also generated by the Marchenko method. We demonstrate the method on a synthetic dataset and successfully apply it to a field dataset acquired in a deep-water salt environment in the Gulf of Mexico. After the successful source wavelet estimation for the field dataset, we create sub-salt target-oriented images with Marchenko redatumed data. Marchenko images using the proposed source wavelet estimation show clear improvements, such as increased continuity of reflectors, compared to surface-based images and to conventional Marchenko images computed without the inverted source wavelet. Our improvements are corroborated by evidence in the literature and our own synthetic results. 相似文献
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