IPG Photonics

About: IPG Photonics is a based out in . It is known for research contribution in the topics: Laser & Fiber laser. The organization has 903 authors who have published 1241 publications receiving 63339 citations.

Constraint on the S‐wave velocity at the base of the mantle

Abstract: Some recent seismic studies have suggested the presence of a thin ultra-low P-wave velocity layer (ULVZ) at the base of the mantle, which is interpreted to be due to presence of partial melting. Partial melting would lead to a strong decrease of the S-wave velocity for which there is no seismic evidence. Such a decrease in the S-wave velocity would produce a strong precursor to SKS phase from the conversion of S to P at the upper boundary of the layer. We analyze records of events from the subduction zones in the south-west Pacific region obtained at stations in North America. At the source side, the converted phases propagate in the region, where the ultra-low P-wave velocity has been found earlier. Our analysis demonstrates that either the S-wave velocity drop in this layer is much smaller than predicted by the hypothesis of melting, or the layer is so thin (less than about 10–15 km) that it can not be detected with our technique.

Silica polymorphs, glass and melt: An in situ high temperature XAS study at the Si K-edge

Abstract: High temperature X-ray absorption spectra at the Si K-edge were obtained for SiO 2 quartz from room temperature up to 2030 K. Important modifications are observed for the XANES spectra. These change are related to rearrangements of the SiO 4 tetrahedra beyond the short-range correlations. To interpret these spectral evolutions, SiO 2 polymorph samples were observed at room temperature and XANES calculations using FDMNES were performed. Very strong differences are shown between the different polymorphs even between α and β phases for which only small displacive angle rotations of the SiO 4 tetrahadra occurs. Therefore the quartz α to β transition could be identified at its expected temperature, 842 K. A badly defined transition toward β-cristobalite is observed between 1670 and 1940 K. The dynamics of this totally reconstructive transition was further investigated on heat treated cherts. Finally the liquid is reached around 2000 K. Many similarities were observed on SiO 2 between its glass at room temperature, β-cristobalite and liquid at high temperature.

Thermodiffusional transport of electrolytes in compact clays

Abstract: The macroscopic Soret coefficient S(T) was measured for three porous media, namely mica, glass powder, and natural compact clay. At a mean temperature of T = 25 degrees C and with NaCl, S(T) for mica and glass powder was found to be equal to (3.1+/-0.7) x 10(-3) K(-1) and close to values for a free medium in agreement with theoretical predictions which are obtained under the assumption that the pressure gradient and the electric field are negligible on the pore scale. The main result is that for clay S(T) was found five times larger, presumably because of extra couplings with electrical phenomena. This latter measurement was confirmed by an independent technique based on the membrane potential.

The tectonics and active faulting of Haiti from seismicity and tomography

Abstract: Oblique convergence of the Caribbean and North American plates has partitioned strain across a major transpressional fault system that bisects the island of Hispaniola. The devastating M W 7.0, 2010 earthquake that struck southern Haiti, rupturing an unknown fault, highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation. Here we assess seismic activity and fault structures across Haiti using data from 33 broadband seismic stations deployed for 16 months. We use traveltime tomography to obtain relocated hypocenters and models of V p and V p /V s crustal structure. Earthquake locations reveal two clusters of seismic activity. The first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture. The second cluster shows shallow activity north of Lake Enriquillo (Dominican Republic), interpreted to have occurred on a north-dipping thrust fault. Crustal seismic velocities show a narrow low-velocity region with an increased V p /V s ratio (1.80-1.85) dipping underneath the Massif de la Selle, which coincides with a southward-dipping zone of hypocenters to a depth of 20 km beneath southern Haiti. Our observations of seismicity and crustal structure in southern Haiti suggests a transition in the Enriquillo fault system from a near vertical strike-slip fault along the Southern Peninsula to a southward-dipping oblique-slip fault along the southern border of the Cul-de-Sac-Enriquillo basin. This result, consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the Enriquillo fault system, is an important constraint in our understanding of regional seismic hazard.