Seismic surveys along subduction zones have identified anomalously high ratio of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust that are possibly due to the presence of pore water. ...Such interpretations postulate that the pore structure is homogeneous at the scale of the seismic wavelength. Here we present the first statistical evidence of a heterogeneous pore structure in oceanic crust at scales larger than laboratory samples. The spatial correlation of measured bulk density profiles of the crustal section of the Samail ophiolite suggests that the pore structure is heterogeneous at scales smaller than ∼1 m. Wave‐induced fluid flow cannot follow the loading during the seismic wave propagation at this estimated heterogeneity, which implies that fluid‐filled microscopic pores and cracks have a limited impact on the observed high VP/VS anomalies in the subducting oceanic crust. Large‐scale cracks may therefore play an important role in shaping these anomalies.
Plain Language Summary
Seismic studies along subduction zones have identified unusually high ratios of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust, which indicates the presence of water‐filled cracks and pores. The close link between pore water and local seismic activity highlights the importance of quantitatively interpreting these seismic anomalies in terms of pore characteristics. Previous interpretations have assumed that the microscopic pore structure is quite homogeneous, even at macroscopic scales as large as the seismic wavelength. However, our analysis of a bulk density profile of the crustal section of the Samail ophiolite, Oman, which is a fossilized oceanic plate preserved on land, indicates that the pore structure is more heterogeneous than previously assumed. This means that the fluid flow within the unit volume that represents the macroscopic physical properties of the rock cannot follow the wave‐induced loading during seismic wave propagations. This results in a relatively small impact of water on the seismic velocity, as inferred from theoretical models that predict the effective elastic properties of rock containing fluid‐filled cracks. Therefore, microscopic cracks may not have a large impact on the high VP/VS values of subducting oceanic crust, whereas large‐scale cracks may play a more significant role.
Key Points
The bulk density of the crustal section of the Samail ophiolite is more spatially heterogeneous than previously assumed
The effect of fluid‐saturated microcracks on low‐frequency seismic velocities is modeled as an unrelaxed condition for this heterogeneity
The high VP/VS anomaly in the subducting oceanic crust can be explained by both microcracks and large‐scale cracks
To assess the paleo‐permeability structure of oceanic crust, we used 3‐D X‐ray Computed Tomography (XCT) images to quantify the distribution and geometry of mineral veins in core samples from Oman ...Drilling Project Holes GT1A, GT2A, and GT3A, which correspond to the upper to lower crustal sections of the Samail ophiolite. We developed a new method that automatically detects veins in the XCT core images based on iterative adaption of the two‐step Hough transform combined with multiscale Hessian filtering for identifying an elongate structure. Application of the developed method allowed us to identify the geometry and Computed Tomography number of more than 1500 veins with millimeter‐scale apertures in core sections with a total length of ∼1,200 m. High‐CT (HCT) veins in the drilled cores can be related to relatively high‐temperature fluid circulation near the mid‐ocean ridge, whereas Low‐CT (LCT) veins can be related to subsequent low‐temperature fluid circulation. Applying fracture fluid‐flow models to the geometric information for the detected veins, we found that the HCT and LCT vein systems both yielded bulk permeability of 10−13–10−9 m2 for each hole. This indicates that millimeter‐wide fractures can control crustal‐scale permeability, even in the lower oceanic crust. However, these vein systems show different depth dependencies and anisotropies of permeability, possibly reflecting the different spatial variations of high‐ and low‐temperature fluid circulation in oceanic crust.
Plain Language Summary
Water transported through fractures in the oceanic crust plays a key role in various geologic processes, such as global transfers of heat and elements moving with fluid. Such fractures are preserved in crustal rocks as mineral veins; therefore, the geometries of the veins can be used to estimate the paleo‐permeability of the fractured rocks. During this study, we investigated the distribution and geometry of veins in core samples of oceanic crust from the Samail ophiolite in Oman to determine its paleo‐permeability structure. The ophiolite represents fragments of ancient oceanic lithosphere obducted onto the continental margin. We quantified three‐dimensional geometric and material information for the veins using 3‐D X‐ray Computed Tomography images of the core samples. Applying fracture fluid‐flow models to the vein data, we found that the oceanic crust had a markedly high permeability, even at depths of several kilometers immediately after the formation of the fractures. We also found that the hydrothermal systems have different spatial variations and anisotropies depending on the CT numbers of the vein‐filling minerals. Our results indicate that there may be differences in the mechanisms of high‐ and low‐temperature hydrothermal circulation in oceanic crust.
Key Points
A new method has been developed to automatically detect vein characteristics from X‐ray Computed Tomography (CT) images of drilled cores
The permeability structure of the crustal section of the Samail ophiolite was estimated from the downhole profiles of detected veins
Permeability structures of High‐CT and Low‐CT vein systems have different spatial variations and anisotropies
Summary
During the 2011 International Pigment Cell Conference (IPCC), the Vitiligo European Taskforce (VETF) convened a consensus conference on issues of global importance for vitiligo clinical ...research. As suggested by an international panel of experts, the conference focused on four topics: classification and nomenclature; definition of stable disease; definition of Koebner’s phenomenon (KP); and ‘autoimmune vitiligo’. These topics were discussed in seven working groups representing different geographical regions. A consensus emerged that segmental vitiligo be classified separately from all other forms of vitiligo and that the term ‘vitiligo’ be used as an umbrella term for all non‐segmental forms of vitiligo, including ‘mixed vitiligo’ in which segmental and non‐segmental vitiligo are combined and which is considered a subgroup of vitiligo. Further, the conference recommends that disease stability be best assessed based on the stability of individual lesions rather than the overall stability of the disease as the latter is difficult to define precisely and reliably. The conference also endorsed the classification of KP for vitiligo as proposed by the VETF (history based, clinical observation based, or experimentally induced). Lastly, the conference agreed that ‘autoimmune vitiligo’ should not be used as a separate classification as published evidence indicates that the pathophysiology of all forms of vitiligo likely involves autoimmune or inflammatory mechanisms.
Background and objectives
Itch is one of the major symptoms in dermatology clinics, and severely impairs the quality of life. Itch is frequently produced by environmental stimuli, especially heat or ...warmth. Changes of temperature on the skin surface and noxious heat stimuli augment and develop itch, respectively. Thermally provoked itch is sometimes intractable with existing treatments.
Data bases and data treatment
Recent researches, linking heat sensation and itch, were searched in MEDLINE literature database through PubMed.
Results
Recent studies of the transient receptor potential cation channel subfamily vanilloid type 1 (TRPV1), the calcitonin gene‐related peptide (CGRP) and the vesicular glutamate transporter 2 (VGLUT2), which link noxious heat and itch, contribute to a much better understanding of the thermally evoked itch process. From a clinical perspective, a warm sensation is a major provocative factor for subjects with atopic dermatitis. The accumulation of artemin (also known as enovin or neublastin) in the dermis of lesional skin can possibly provide a pathological mechanism for warmth‐provoked itch.
Conclusions
This mini‐review describes recent results of both basic and clinical research related to thermally provoked itch.
Supported by laboratory experimental results, the reduction in elastic thickness (Te ${T}_{e}$) and flexural rigidity (D $D$) at trench outer rise, which enables bending, is attributed to damage. A ...series of laboratory experiments were performed on intact and thermally treated diabase and peridotite (400°C–800°C) under increasing confining pressures (3–200 MPa) at room temperature. Simultaneous porosity and elastic wave velocity (P and S) measurements were obtained under dry and fluid saturated conditions. The velocity and porosity inversions indicated a significant variation in crack properties (crack density, aspect ratio) and reduction in Young's modulus, of thermally treated samples in comparison to the intact samples. Hence the experimental results suggested weakening in elastic properties of a damaged oceanic lithosphere. Subsequently created lithospheric strength profiles showed a strength reduction in wet models in comparison to dry models. Under the assumption of different cooling models, the aging of the plate resulted in an increase in strength with deeper neutral zones. The outcome of the strength profiles was utilized to estimate Te ${T}_{e}$ and D $D$, which are also dependent on the elasticity of the lithosphere. The results showed a reduction in D $D$ with increasing damage and suggest that the bending at the subduction zone is facilitated by weakened elastic properties of a damaged lithosphere. While most of the geophysical observations of Te ${T}_{e}$ were able to be constrained by the proposed damaged models, some shallow observations indicated enhanced damage triggered either by increased depth to brittle‐ductile transition or by large bending related faulting events.
Plain Language Summary
In this investigation, we propose that the bending of the plate at the subduction zone is facilitated by cracks that are present in the rocks. To test this idea, we conducted several experiments in the laboratory on rocks which represent the oceanic plate (diabase and peridotite). By increasing the temperature inside a furnace, we induced cracks (damage) in the samples before the experiments and compared the results with the undamaged samples. During the experiment, we measured the wave velocity and porosity. From the comparison, it was understood that the damaged rocks have weak elastic properties. Following the results of the experiments, we calculated the lithospheric strength profiles, for both dry and wet models for different ages of the oceanic plate and found that the strength decrease markedly when water is present. From this strength estimations, we calculated the thickness of the elastic layer which can transmit bending stress and the flexural rigidity which is the resistance to bending. The results showed that with more damage present in the plate, the elastic thickness and flexural rigidity decrease. Finally, we compared these results with the actual geophysical data and have shown the validity of our model.
Key Points
Hydrostatic experiments were conducted on thermally treated diabase and peridotite with simultaneous velocity and porosity measurements
Damaged models showed significant weakening in the elastic properties of the rocks due to the development of cracks
Supported by the experimental results, elastic thickness, and rigidity of dry and wet oceanic lithospheres were estimated
The influence of water and stress on the lattice-preferred orientation (LPO) of olivine aggregates was investigated through large strain, shear deformation experiments at high pressures and ...temperatures (
P
=
0.5–2.1 GPa,
T
=
1470–1570 K) under both water-poor and water-rich conditions. The specimens are hot-pressed synthetic olivine aggregates or single crystals of olivine. Water was supplied to the sample by decomposition of a mixture of talc and brucite. Deformation experiments were conducted up to
γ (shear strain)
∼
6 using the Griggs apparatus where water fugacity was up to ∼ 13 GPa at the pressure of 2 GPa. The water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at
P
=
0.5–2 GPa was ∼ 400–1200 ppm H/Si. Several new types of LPO in olivine are found depending on water content and stress. Samples deformed in water-poor conditions show a conventional LPO of olivine where the olivine 100 axis is subparallel to the shear direction, the (010) plane subparallel to the shear plane (type-A). However, we identified three new types (type-B, C, and E) of LPO of olivine depending on the water content and stress. The type-B LPO of olivine which was found at relatively high stress and/or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction, the (010) plane subparallel to the shear plane. The type-C LPO which was found at low stress and under water-rich conditions is characterized by the olivine 001 axis subparallel to the shear direction, the (100) plane subparallel to the shear plane. The type-E LPO which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction, the (001) plane subparallel to the shear plane. Observations by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) show that the dislocations in water-poor samples (type-A) are curved and both
b
=
100 and
b
=
001 dislocations have a similar population. Numerous subgrains are seen in water-poor samples in backscattered electron images. In contrast, water-rich samples (both type-B and type-C) contain mostly
b
=
001 dislocations and dislocations are straight and sub-grain boundaries are rare compared to those in water-poor samples. These observations suggest that (1) dominant slip systems in olivine change with water fugacity (and stress) and (2) grain boundary migration is enhanced in the presence of water. Seismic anisotropy corresponding to the fabrics under water-rich condition is significantly different from that under water-poor condition. Consequently, the relationship between seismic anisotropy and flow geometry in water-rich regions is expected to be different from that in water-poor regions in which type-A fabric dominates (i.e., the lithosphere). A few cases are discussed including anisotropy in the subduction zone and in the deep upper mantle.
The ferroelectric soft mode in a SrTiO(3) thin film was impulsively driven to a large amplitude using intense picosecond terahertz pulses. As the terahertz electric field increased, the soft-mode ...absorption peak exhibited blueshifting and spectral narrowing. A classical anharmonic oscillator model suggests that the induced displacement is comparable to that of the ferroelectric phase transition. The spectral narrowing indicates that the displacement exceeds that induced by any inhomogeneities in the film, demonstrating that the method can be used to explore intrinsic quartic anharmonicity.
Cores recovered during the International Continental Scientific Drilling Program project “Drilling into Seismogenic zones of M2.0 to M5.5 earthquakes in deep South African Gold Mines” include fault ...breccia from within the aftershock cloud of the 2014 Orkney earthquake (M5.5). The breccia and surrounding intrusive rocks, probably lamprophyres rich in talc, biotite, calcite, and amphibole, had high magnetic susceptibilities owing to the presence of magnetite. All of these characteristics can be attributed to fluid‐related alteration. Both the breccia and the lamprophyres had low friction coefficients and showed evidence of velocity strengthening, which is inconsistent with the occurrence of earthquakes. Variable amounts of talc, biotite, calcite, and amphibole within the lamprophyres might have produced complex frictional properties and spatial heterogeneity of fault stability. The altered lamprophyres may be the host rocks of the 2014 Orkney earthquake, but frictional complexity may have governed the magnitudes of the main‐ and aftershocks and their distributions.
Plain Language Summary
Drilling into seismogenic zones is an important scientific endeavor, not only to advance our understanding of the mechanisms of earthquakes, but also to provide information that will improve the resilience of humankind to these deadly hazards. The International Continental Scientific Drilling Program supported deep drilling into the aftershock region of the 2014 Orkney earthquake (M5.5) and successfully recovered samples of faulted rock material from about 3.3 km depth by drilling from a depth of about 3 km in a South African gold mine. The samples were intensively sheared and rich in talc, which is a weak mineral with a very low friction coefficient. The fault zone probably developed within this talc‐rich rock, which would indicate that the earthquake was closely related to a pre‐existing weak geological structure. However, other minerals in the fault rocks might also have influenced the spatial heterogeneity of fault stability and earthquake generation.
Key Points
Fault breccia was recovered from within the aftershock cloud of the 2014 Orkney earthquake (M5.5)
The fault breccia and surrounding altered lamprophyres had high talc contents and low friction coefficients
Variable amounts of talc, biotite, calcite, and amphibole might have produced complex friction properties in the lamprophyres
What is the origin of molecular friction, and how can macroscopic friction be explained in terms of molecular friction? To elucidate the origins of molecular and macroscopic friction, we conducted ...density functional theory calculations and double-direct shear tests at normal stresses ranging from 5 to 60 MPa for mica surfaces. Frictional forces between mica surfaces were theoretically predicted to oscillate periodically every 30° of sliding direction, in agreement with previous experimental findings. This result affirms that the potential energy roughness of mica under sliding is the origin of molecular friction, which depends on the normal stress and sliding direction. The discovered mechanism of molecular friction can quantitatively explain experimentally observed macroscopic friction of mica when the presence of wear particles is taken into consideration.
Dacarbazine (DTIC) is one of the most popular alkylating agents used for the treatment of malignant melanoma. DTIC induces apoptosis of melanoma cells via double-strand breaks (DSBs). Melanoma cells, ...however, tend to increase their expression of DNA repair molecules in order to be resistant to DTIC. Here, we show that DTIC increases expression of Rad51, but not Ku70, in a cultured B16-F10 mouse melanoma cell line in dose- and time-dependent manners. On introducing Rad51 short interfering RNA (siRNA) with the hemagglutinating virus of Japan envelope (HVJ-E) to B16-F10 cells, DSBs induced by DTIC treatment were not efficiently repaired and resulted in enhanced apoptotic cell death. Colony formation of B16-F10 cells that received Rad51 siRNA was significantly decreased by DTIC treatment as compared with cells that received scramble siRNA. In melanoma-bearing mice, the combination of three intratumoral injections of HVJ-E containing Rad51 siRNA and five intraperitoneal injections of DTIC at a clinical dose synergistically suppressed the tumors. Moreover, HVJ-E demonstrated anti-tumor immunity by inducing cytotoxic T lymphocytes to B16-F10 cells on administration of DTIC. These results suggest that the combination of chemotherapy with HVJ-E containing therapeutic molecules will provide a promising therapeutic strategy for patients bearing malignant tumors resistant to chemotherapeutic agents.
PDF
