Wax esters and triacylglycerols in sinking particulate matter in the Peru upwelling area (15°S, 75°W)

The flux and composition of wax esters and triacylglycerols were measured in particulate matter collected by free-drifting sediment traps in the Peru upwelling area. The purpose was to assess diurnal variations in sources and vertical transport of these lipids. Traps were deployed for periods of 8–12 h during both day and night at the base of the euphotic zone (10–14m) and at about 50m. Although the flux of total particulate organic carbon varied 4×, the flux of wax esters varied by 84× and triacylglycerols by 30×. POC, wax esters, and triacylglycerols also showed different temporal patterns. The highest wax ester flux was measured in shallow traps at night and is attributed to increased inputs from zooplankton which feed near the surface at night. Triacylglycerol flux was high in both shallow and deep nocturnal traps, consistent with inputs of both phytoplankton and zooplankton lipids. The composition of these lipids was also quite variable and attests to the complex nature of the lipid sources.     

Shear-wave polarizations near the North Anatolian Fault – I. Evidence for anisotropy-induced shear-wave splitting

Summary. The Turkish Dilatancy Projects (TDP1 in 1979 and TDP2 in 1980) recorded small earthquakes near the North Anatolian Fault with closely-spaced networks of three-component seismometers in order to investigate the possibility of diagnosing dilatancy from its effects of shear-wave propagation. This paper examines the polarizations of shear wavetrains recorded in the shear-wave window immediately above the earthquake foci. Abrupt changes in the orientation and/or ellipticity of the shear-wave polarizations are almost always observed during the first few cycles following the initial shear-wave arrival on each seismogram. The horizontal projections of the polarizations of the first shear-wave arrivals at any given station show nearly parallel alignments with approximately the same orientations at each of the recording sites (with one exception). It is difficult to explain this uniform alignment over a wide area in terms of scattering at the irregular surface topography or by earthquake focal mechanisms. We demonstrate that the shear-wave splitting is likely to be the result of anisotropy in the region above the earthquake foci, which could produce polarizations displaying the observed alignments. The temporal change of the azimuth of alignment, observed at one locality between 1979 and 1980, may be due to the release of a local stress anomaly by a very near earthquake.     

Collisional history of asteroids: Evidence from Vesta and the Hirayama families

Collisional evolution studies of asteroids indicate that the initial asteroid population at the time mean collisional velocities were pumped up to ～5 km/sec was only modestly larger than it is today; i.e., the asteroid belt was already depleted relative to the mean surface density elsewhere in the planetary region. Numerical simulations of the collisional evolution of hypothetical initial asteroid populations have been run, subject to three constraints: they must (a) evolve to the present observed asteroid size distribution, (b) preserve Vesta's basaltic crust, and (c) produce at least the observed number of major Hirayama families. A “runaway growth” initial asteroid population distribution is found to best satisfy these constraints. A new model is presented for calculating the fragmental size distribution for the disruption of large, gravitationally bound bodies in which the material strength is increased by hydrostatic self-compression. This model predicts that large asteroid behave as intrinsically strong bodies, even if they have had a history of being collisionally fractured. This model, when applied to the breakup of the Themis and Eos family parent bodies, gives size distributions in reasonably good agreement with those observed.     

Geological and hydrogeological assessment of the Brito Formation: Municipio de Tola,Nicaragua

Hydrogeology Journal - There are sparse hydrogeological data and insufficient hydrogeological knowledge in many areas of the world reliant on groundwater. Nicaragua’s Pacific coast is one...