Plate-Boundary Kinematics of the Afrera Linkage Zone (Afar) From InSAR and Seismicity

International audienceStudying the mechanisms of interaction between rift segments is key to understanding the kinematics of plate boundaries in continental rifts. However, the spatial and temporal evolution of deformation at rift linkage zones is rarely observed directly. Here, we combine InSAR data spanning 2005–2010 and 2014–2019 from ENVISAT and Sentinel-1 satellites, respectively, with local seismicity from the Afar rift to investigate the plate-boundary kinematics of the Afrera linkage zone, the junction between the Erta Ale and Tat Ali magmatic segments in Northern Afar (Ethiopia). We obtain time-series of cumulative InSAR Line-Of-Sight (LOS) displacements that show deformation is accommodated by a series of active en-echelon faults striking ∼NS and characterized by normal slip associated with a left-lateral strike-slip component. Additionally, we observe spatial variation in fault behavior with stick-slip and creep. The faults in the center of the linkage zone behave primarily in a stick-slip mode (with abrupt fault displacements up to ∼40 mm) and fault motions are associated with earthquakes of ML > 5. Conversely, faults at the edge of the linkage zone, near the magmatic segments, show creep and some stick-slip behavior (with cumulative LOS displacement up to ∼30–40 mm over a ∼5-year period) accompanied by low-level seismicity. Some of the creeping faults are also spatially associated with hydrothermal springs. We interpret that the temporal behavior of the faults in the linkage zone is controlled by the interplay between tectonic extension, high heat flows, and fluid circulation near the magmatic segments where creeping of some faults is favored

Computer simulations of domain growth and phase separation in two-dimensional binary immiscible fluids using dissipative particle dynamics

We investigate the dynamical behavior of binary fluid systems in two dimensions using dissipative particle dynamics. We find that following a symmetric quench the domain size R(t) grows with time t according to two distinct algebraic laws R(t) = t^n: at early times n = 1/2, while for later times n = 2/3. Following an asymmetric quench we observe only n = 1/2, and if momentum conservation is violated we see n = 1/3 at early times. Bubble simulations confirm the existence of a finite surface tension and the validity of Laplace's law. Our results are compared with similar simulations which have been performed previously using molecular dynamics, lattice-gas and lattice-Boltzmann automata, and Langevin dynamics. We conclude that dissipative particle dynamics is a promising method for simulating fluid properties in such systems.Comment: RevTeX; 22 pages, 5 low-resolution figures. For full-resolution figures, connect to http://www.tcm.phy.cam.ac.uk/~ken21/tension/tension.htm

Differentiating flow, melt, or fossil seismic anisotropy beneath Ethiopia

Ethiopia is a region where continental rifting gives way to oceanic spreading. Yet the role that pre-existing lithospheric structure, melt, mantle flow, or active upwellings may play in this process is debated. Measurements of seismic anisotropy are often used to attempt to understand the contribution that these mechanisms may play. In this study, we use new data in Afar, Ethiopia along with legacy data across Ethiopia, Djibouti, and Yemen to obtain estimates of mantle anisotropy using SKS-wave splitting. We show that two layers of anisotropy exist, and we directly invert for these. We show that fossil anisotropy with fast directions oriented northeast-southwest may be preserved in the lithosphere away from the rift. Beneath the Main Ethiopian Rift and parts of Afar, anisotropy due to shear segregated melt along sharp changes in lithospheric thickness dominates the shear-wave splitting signal in the mantle. Beneath Afar, away from regions with significant lithospheric topography, melt pockets associated with the crustal and uppermost mantle magma storage dominate the signal in localized regions. In general, little anisotropy is seen in the uppermost mantle beneath Afar suggesting melt retains no preferential alignment. These results show the important role melt plays in weakening the lithosphere and imply that as rifting evolves passive upwelling sustains extension. A dominant northeast-southwest anisotropic fast direction is observed in a deeper layer across all of Ethiopia. This suggests that a conduit like plume is lacking beneath Afar today, rather a broad flow from the southwest dominates flow in the upper mantle

Marathon related death due to brainstem herniation in rehydration-related hyponatraemia: a case report

Introduction: Identifying marathon runners at risk of neurological deterioration at the end of the race (within a large cohort complaining of exhaustion, dehydration, nausea, headache, dizziness, etc.) is challenging. Here we report a case of rehydration-related hyponatraemia with ensuing brain herniation. Case presentation: We report the death of runner in his 30's who collapsed in the recovery area following a marathon. Following rehydration he developed a respiratory arrest in the emergency room. He was found to be hyponatraemic (130 mM). A CT brain scan showed severe hydrocephalus and brain stem herniation. Despite emergency insertion of an extraventricular drain, he was tested for brainstem death the following morning. Funduscopy demonstrated an acute-on-chronic papilledema; CSF spectrophotometry did not reveal any trace of oxyhemoglobin or bilirubin, but ferritin levels were considerably raised (530 ng/mL, upper reference value 12 ng/mL), consistent with a previous bleed. Retrospectively it emerged that the patient had suffered from a thunderclap headache some months earlier. Subsequently he developed morning headaches and nausea. This suggests that he may have suffered from a subarachnoid haemorrhage complicated by secondary hydrocephalus. This would explain why in this case the relatively mild rehydration-related hyponatremia may have caused brain swelling sufficient for herniation. Conclusion: Given the frequency of hyponatraemia in marathon runners (serum Na <135 mM in about 13%), and the non-specific symptoms, we discuss how a simple screening test such as funduscopy may help to identify those who require urgent neuroimaging

A comparative force assessment of 4 methods to move a patient up a bed

This study compared four different postures and positions regularly suggested for moving a patient up towards the head of the bed, using both novice and expert users. The trial was carried out in a laboratory using 21 participants (10 novices and 11 experts). All participants completed all conditions (n = 4) three times each (n = 3 repetitions). The physical force at each hand was recorded using electronic four compression/tension meters, recorded on DasyLab software. After each condition a subjective review questionnaire was completed. The data was processed with excel and SPSS to evaluate the differences between the conditions. A significant statistical reduction was found when comparing combined force for all carers (F(3,27) = 24.63, p <.05) and the load per individual (F(2.21,44.21) = 27.26, p <.05). However there was found to be no statistical difference between left and right hand or upper or lower hand. Transfers carried out with the carer pulling the patient towards them corresponded with a lower force to complete the transfer. This study suggests that a position with an oblique offset base and an action of pull and push in line with the carer could be the preferred position for a wide range of patient transfers

Using salt counterions to modify β2-agonist behaviour in vivo

This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. © 2016 American Chemical Society.There is a paucity of data describing the impact of salt counterions on the biological performance of inhaled medicines in vivo. The aim of this study was to determine if the coadministration of salt counterions influenced the tissue permeability and airway smooth muscle relaxation potential of salbutamol, formoterol, and salmeterol. The results demonstrated that only salbutamol, when formulated with an excess of the 1-hydroxy-2-naphthoate (1H2NA) counterion, exhibited a superior bronchodilator effect (p < 0.05) compared to salbutamol base. The counterions aspartate, maleate, fumarate, and 1H2NA had no effect on the ability of formoterol or salmeterol to reduce airway resistance in vivo. Studies using guinea pig tracheal sections showed that the salbutamol:1H2NA combination resulted in a significantly faster (p < 0.05) rate of tissue transport compared to salbutamol base. Furthermore, when the relaxant activity of salbutamol was assessed in vitro using electrically stimulated, superfused preparations of guinea pig trachea, the inhibition of contraction by salbutamol in the presence of 1H2NA was greater than with salbutamol base (a total inhibition of 94.13%, p < 0.05). The reason for the modification of salbutamol’s behavior upon administration with 1H2NA was assigned to ion-pair formation, which was identified using infrared spectroscopy. Ion-pair formation is known to modify a drug’s physicochemical properties, and the data from this study suggested that the choice of counterion in inhaled pharmaceutical salts should be considered carefully as it has the potential to alter drug action in vivo.Peer reviewe