Tuesday, July 2, 2013

Question Answering for Abstract

1• What are seismic waves and how are they formed?

     Seismic waves are waves of energy that travel through the Earth's layers, and are a result of an earthquake,  
     explosion, or a volcano that imparts low-frequency acoustic energy. Many other natural and anthropogenic 
      sources create low amplitude waves commonly referred to as ambient vibrations.

2• What are the types of Seismic Waves?

Primary waves

Primary waves (P-waves) are compressional waves that are longitudinal in nature. P waves are pressure waves that travel faster than other waves through the earth to arrive at seismograph stations first hence the name "Primary". These waves can travel through any type of material, including fluids, and can travel at nearly twice the speed of S waves. In air, they take the form of sound waves, hence they travel at the speed of sound. Typical speeds are 330 m/s in air, 1450 m/s in water and about 5000 m/s in granite. Primary waves also travel about 1 to 5 miles per second (1.6 to 8 kps), depending on the material they're moving through.

Secondary waves

Secondary waves (S-waves) are shear waves that are transverse in nature. These waves arrive at seismograph stations after the faster moving P waves during an earthquake and displace the ground perpendicular to the direction of propagation. Depending on the propagational direction, the wave can take on different surface characteristics; for example, in the case of horizontally polarized S waves, the ground moves alternately to one side and then the other. S waves can travel only through solids, as fluids (liquids and gases) do not support shear stresses. S waves are slower than P waves, and speeds are typically around 60% of that of P waves in any given material.

Body waves

Body waves travel through the interior of the Earth.

Surface waves

Surface waves (L-waves) are analogous to water waves and travel along the Earth's surface.

Rayleigh waves

Rayleigh waves are surface waves that travel as ripples with motions that are similar to those of waves on the surface of water.

Love waves

Love waves are horizontally polarized shear waves.

Stoneley waves

A Stoneley wave is a type of large amplitude Rayleigh wave that propagates along a solid-fluid boundary.

3• Why is it important to analyse seismic waves?

Seismic waves is used for research into the structure of the Earth's interior, and man made vibrations are often generated to investigate shallow, subsurface structures.

4• What seismic waves are used to locate epicenters for earthquakes?

Earthquakes produce two waves, the primary (p) and secondary (s) waves. The have different vibration directions and different speeds. For precision both waves are used and triangulated by using 2 or more seismographic receiving stations (Often people say you need 3 stations but this is a mistake, The third point of the triangulation is the epicenter. More stations add precision.) Because the speed of the waves are different you can get an estimate off how far away the epicenter is by timing the separation of the p and s waves.

5• What equipment is used for the experiment?

It requires the Global Earthquake Explorer program to be downloaded to analyze data from a global seismic network, by using seismographs. A high speed internet access would also be required.

6• What  is a example of research done on seismic waves?

The development of seismic wave study in China in the past four years is reviewed. The discussion is divided into several aspects, including seismic wave propagation in laterally homogeneous media, laterally heterogeneous media, anisotropic and porous media, surface wave and seismic wave inversion, and seismic wave study in prospecting and logging problems. Important projects in the current studies on seismic wave is suggested as the development of high efficient numerical methods, and applying them to the studies of excitation and propagation of seismic waves in complex media and strong ground motion, which will form a foundation for refined earthquake hazard analysis and prediction.

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