Three-Dimensional Modeling of Shallow Shear-Wave Velocities for Las Vegas, Nevada, Using Sediment Type

A three-dimensional model of near-surface shear-wave velocity in the deep alluvial basin underlying the metropolitan area of Las Vegas, Nevada （USA）, is being developed for earthquake site response projections. The velocity dataset, which includes 230 measurements, is interpolated across the model using depth-dependent correlations of velocity with sediment type. The sediment-type database contains more than 1 400 well and borehole logs. Sediment sequences reported in logs are assigned to one of four units. A characteristic shear-wave velocity profile is developed for each unit by analyzing closely spaced pairs of velocity profiles and well or borehole logs. The resulting velocity model exhibits reasonable values and patterns, although it does not explicitly honor the measured shear-wave velocity profiles. Site response investigations that applied a preliminary version of the velocity model support a two-zone ground-shaking hazard model for the valley. Areas in which clay predominates in the upper 30 m are predicted to have stronger ground motions than the rest of the basin.

Temporal variation of resource allocation between sexual and asexual structures in response to nutrient and water stress in a floating-leaved plant

Aims Adaptive plasticity of biomass allocation to different environmental stressors enables plants to maintain functional relationships among reproductive structures.In freshwater systems,water depth and nutrient content of sediments can have a major effect on biomass allocation in aquatic macrophytes.However,the relative importance of these two stressors is unknown as it is the temporal variation of biomass allocation to the stressors during the growing period.This information may be critical for understanding the tolerance of a plant to environmental conditions.Methods Here,we used four levels of environmental stressors generated by deep and shallow water and high or low sediment nutrient content in a factorial experiment to investigate the biomass allocation responses of a floating macrophyte,Trapella sinensis,during the growing period.Important Findings The results showed that the lower sediment nutrient content inhibited biomass increase,whereas the lower water depth increased the sexual reproduction of the plants.The lower sediment content also led to a delay in flowering and compensated trade-offs among sexual reproduction and elongation and clonal reproduction during the growing period.These results indicated that water depth affected the ratio of biomass allocation,whereas the sediment nutrient content affected biomass accumulation when the plants faced these two environmental factors simultaneously.The temporal changes in allocation under lower sediment nutrient content underscored the importance of collecting data at different stages of growth when trying to interpret resource allocation,especially in resource-limited environments.