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Following the linearized attenuation tomography from our previous study (Pejić et al., 2017, https://doi.org/10.1002/2016JB013692), we perform hierarchical transdimensional Bayesian tomography of the upper ≈400 km of the inner core, using 398 globally distributed t∗ estimates. The results are in good agreement with the ones obtained through linearized tomography: they show more complex attenuation pattern than the purely hemispherical one, and the noise estimated from the hierarchical inversion is in good agreement with estimates obtained from the Discrepancy Principle in the previous study. The attenuation pattern we observe gives more weight to the geodynamical models that couple the thermal anomalies of the lowermost mantle to the inner core boundary. Key Points: Transdimensional sampling of Voronoi cells on a spherical surface applied to a problem in global tomographyNo hemispherical pattern is observed in attenuation structure of the upper inner coreThe study provides a strong seismological hint for a strongly attenuating inner core [ABSTRACT FROM AUTHOR]

An investigation of the ion density produced inside the Chi Kung reactor at 250 W and 0.30 mtorr was performed through Langmuir probe measurements. Three-dimensional interpolation combined these data to produce a 3-D density volume. The resulting image was used to identify three distinct regions of differing density: power deposition, acceleration, and expansion. The ion density over these regions was found to vary from ~1.3 × 1010 to ~2.7 × 1011 cm-3. [ABSTRACT FROM AUTHOR]

The evolution of fault strength and behavior during the initial stages of slip plays an important role in driving the onset of instability and fault weakening. Using small-displacement triaxial experiments on quartz sandstone, this study highlights the rapid onset of microstructural change on fault interfaces and identifies new evidence for an evolution in physical processes with increasing slip and velocity. Pre-ground fault surfaces have been slipped over a range of velocities (0.36 μm s-1 to 18 cm s-1) and at normal stresses comparable to upperto mid-crustal conditions (92-287 MPa). Microstructural analysis of the fault interfaces reveals the formation of amorphous material at displacements <170 μm and slip durations < 1 ms. Mechanical and microstructural observations have been combined with numerical modeling to present the first documented examples of a transition from mechanical amorphization to flash heating, then frictional melting, with changes in slip conditions. The sequence of processes activated during the initial stages of fault movement may provide new insights into factors that influence the onset of slip in the seismogenic crust. [ABSTRACT FROM AUTHOR]