Measurements of seismic attenuation and transient fluid pressure in partially saturated Berea sandstone: evidence of fluid flow on the mesoscopic scale

A novel laboratory technique is proposed to investigate wave-induced fluid flow on the mesoscopic scale as a mechanism for seismic attenuation in partially saturated rocks. This technique combines measurements of seismic attenuation in the frequency range from 1 to 100 Hz with measurements of transient fluid pressure as a response of a step stress applied on top of the sample. We used a Berea sandstone sample partially saturated with water. The laboratory results suggest that wave-induced fluid flow on the mesoscopic scale is dominant in partially saturated samples. A 3-D numerical model representing the sample was used to verify the experimental results. Biot's equations of consolidation were solved with the finite-element method. Wave-induced fluid flow on the mesoscopic scale was the only attenuation mechanism accounted for in the numerical solution. The numerically calculated transient fluid pressure reproduced the laboratory data. Moreover, the numerically calculated attenuation, superposed to the frequency-independent matrix anelasticity, reproduced the attenuation measured in the laboratory in the partially saturated sample. This experimental—numerical fit demonstrates that wave-induced fluid flow on the mesoscopic scale and matrix anelasticity are the dominant mechanisms for seismic attenuation in partially saturated Berea sandston

Pore Space Topology Controls Ultrasonic Waveforms in Dry Volcanic Rocks

Pore space controls the mechanical and transport properties of rocks. At the laboratory scale, seismic modeling is usually performed in relatively homogeneous settings, and the influence of the pore space on the recorded wavefields is determined by rock-fluid interactions. Understanding this influence in dry rocks is instrumental for assessing the impact of pore topology on waves propagating in heterogeneous environments, such as volcanoes. Here, we simulated the propagation of shear waves as a function of pore space parameters in computational models built as proxies for volcanic rocks. The spectral-element simulations provide results comparable with ultrasonic experiments, and the outcome shows that the size, shape, volume, and location of pores impact amplitudes and phases. These variations intensify in waveform coda after multiple scattering. Our results confirm that pore topology is one of the primary regulators of the propagation of elastic waves in dry rocks regardless of porosity

Source and dynamics of a volcanic caldera unrest : Campi Flegrei, 1983–84

Acknowledgements We thank Tiziana Vanorio, Antonella Amoruso, Luca Crescentini, Nicholas Rawlinson, Yasuko Takei, and David Cornwell for the valuable suggestions regarding the methodology and interpretation. Reviews from Tim Greenfield and two anonymous reviewers helped improving both clarity of the manuscript and interpretation. The Royal Society of Edinburgh - Accademia dei Lincei Bilateral Agreement, the Santander Mobility Award of the College of Physical Sciences, University of Aberdeen, and the TIDES EU COST action granted L.D.S. travel grants for the realisation of this study. E.D.P. has been supported by the EPHESTO and KNOWAVES projects, funded by the Spanish Ministry of Education and Science.Peer reviewedPublisher PD

Extrinsic elastic anisotropy in a compositionally heterogeneous Earth's mantle

Several theoretical studies indicate that a substantial fraction of the measured seismic anisotropy could be interpreted as extrinsic anisotropy associated with compositional layering in rocks, reducing the significance of strain‐induced intrinsic anisotropy. Here, we quantify the potential contribution of grain‐scale and rock‐scale compositional anisotropy to the observations by (i) combining effective medium theories with realistic estimates of mineral isotropic elastic properties, and (ii) measuring velocities of synthetic seismic waves propagating through modelled strain‐induced microstructures. It is shown that for typical mantle and oceanic crust sub‐solidus compositions, rock‐scale compositional layering does not generate any substantial extrinsic anisotropy (<1%) because of the limited contrast in isotropic elastic moduli among different rocks. Quasi‐laminated structures observed in subducting slabs using P‐ and S‐ wave scattering are often invoked as a source of extrinsic anisotropy, but our calculations show that they only generate minor seismic anisotropy (<0.1‐0.2% of Vp and Vs radial anisotropy). More generally, rock‐scale compositional layering, when present, cannot be detected with seismic anisotropy studies, but mainly with wave scattering. In contrast, when grain‐scale layering is present, significant extrinsic anisotropy could exist in vertically limited levels of the mantle such as in a MORB‐rich lower transition zone or in the uppermost lower mantle where foliated basalts and pyrolites display up to 2‐3% Vp and 3‐6% Vs radial anisotropy. Thus, seismic anisotropy observed around the 660 km discontinuity could be possibly related to grain‐scale SPO. Extrinsic anisotropy can form also in a compositionally homogeneous mantle, where velocity variations associated with major phase transitions can generate up to 1% of positive radial anisotropy

Low-Frequency Elastic Properties of a Polymineralic Carbonate: Laboratory Measurement and Digital Rock Physics

We demonstrate that the static elastic properties of a carbonate sample, comprised of dolomite and calcite, could be accurately predicted by Digital Rock Physics (DRP), a non-invasive testing method for simulating laboratory measurements. We present a state-of-the-art algorithm that uses X-ray Computed Tomography (CT) imagery to compute the elastic properties of a lacustrine rudstone sample. The high-resolution CT-images provide a digital sample that is used for analyzing microstructures and performing quasi-static compression numerical simulations. Here, we present the modified Segmentation-Less method withOut Targets method: a combination of segmentation-based and segmentation-less DRP. This new method assigns the spatial distribution of elastic properties of the sample based on homogenization theory and overcomes the monomineralic limitation of the previous work, allowing the algorithm to be used on polymineralic rocks. The method starts by partitioning CT-images of the sample into smaller sub-images, each of which contains only two phases: a mineral (calcite or dolomite) and air. Then, each sub-image is converted into elastic property arrays. Finally, the elastic property arrays from the sub-images are combined and fed into a finite element algorithm to compute the effective elastic properties of the sample. We compared the numerical results to the laboratory measurements of low-frequency elastic properties. We find that the Young’s moduli of both the dry and the fully saturated sample fall within 10% of the laboratory measurements. Our analysis also shows that segmentation-based DRP should be used cautiously to compute elastic properties of carbonate rocks similar to our sample.ISSN:2296-646

Mesenchymal stromal cells : a new tool against graft-versus-host disease ?

Mesenchymal stromal cells (MSCs) represent a heterogeneous subset of multipotent cells that can be isolated from several tissues including bone marrow and fat. MSCs exhibit immunomodulatory and anti-inflammatory properties that prompted their clinical use as prevention and/or treatment for severe graft-versus-host disease (GVHD). Although a number of phase I-II studies have suggested that MSCs infusion was safe and might be effective for preventing or treating acute GVHD, definitive proof for their efficacy remains lacking thus far. Multicenter randomized studies are ongoing to more precisely assess the impact of MSCs infusion on GVHD prevention/treatment, whereas further research is performed in vitro and in animal models with the aims of determining the best way to expand MSCs ex vivo as well as the most efficient dose and schedule of MSCs administration. After introducing GVHD, MSC biology, and results of MSCs infusion in animal models of allogeneic hematopoietic cell transplantation, this article reviews the results of the first clinical trials investigating the use of MSCs infusion as prevention or treatment of GVHD.Peer reviewe