How granulometric is (grain size) analysis helpful in understanding the depositional environments of the past geological time?
A granulometric analysis is carried out for getting the ranges of grain size and their distribution with respect to phi values (size classes) for a particular sediment layer. Grain size ranges from boulder-size (>256 mm) to clay size (<1/256 mm) in accordance with the relative phi scale. The granulometric analysis gives the gain sizes, i.e. boulder, cobble, pebble, granule, sand, silt, and clay, as well as nature of their distribution by graphics parameters, i.e. Mean, sorting, skewness, and kurtosis. Mean is the average grain size, sorting is the standard deviation from the mean, skewness is the symmetry of distribution and kurtosis is the peak of distribution. These parameters define the nature of grain size ranges in a deposit, which characterizes the mode of sediment transport, duration of transport, process of deposition and type of sedimentary basin in which it was deposited. Depositional environments have characteristic signatures in their deposits; for example, (1) fluvial deposits are usually coarse-grained, well sorted, well rounded, symmetrically distributed with a high peak, (2) Glacial deposits are very poorly sorted, angular shaped, asymmetrically distributed with a wide peak. Similarly, granulometric analysis is helpful in understanding eolian, coastal, lacustrine and marine depositional environments.
How is the internal structure of the Earth determined? How do we know the nature of internal layers of the Earth?
Seismic waves originated from a large earthquake or explosion are divided into two major categories; Body waves and Surface waves. While surface waves travel near the earth surface and cause destruction, Body waves travel through inside of the Earth. There are two types of Body waves; P waves and S waves which can extract information of the Earth's internal structure on passing through its different layers. When P waves and S waves interact with a medium, they either reflected, refracted or directly travel through it. P waves are compressional waves that pass through solids as well as liquids whereas S waves are shear waves that can only pass through solids. Both the waves easily pass through the crust and mantle demonstrating their solid to semi-solid nature, however only P waves can pass through the core demonstrating that outer part of the core is liquid. Based on their transmission abilities through different layers, P waves and S waves shadow zones come into origin. Moreover, the speed of the seismic waves depends on density, so the travel-time relation of seismic waves is used to map change in density with depth, which shows that the Earth is composed of several layers of different natures.
Why are steel plates inserted inside bearings with elastomeric bearings?
In order to make an elastomeric bearing act/ function as a soft spring, it should be made to allow it to bulge laterally and also the stiffness compression can be increased by simply increasing the limiting amount of the lateral bulging. In many cases in order to increase the compression stiffness of the bearing the usage of metal plates is made. Once steel plates are included in the bearings the freedom of the bulge is restricted dramatically, also the deflection of the bearing is reduced as compared to a bearing without the presence of steel plates. The tensile stresses of the bearings are induced into the steel plates. But the presence of the metal plates does not affect the shear stiffness of the bearings.