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It seems that this past year has been filled with all types of strange weather patterns all across the nation.Between droughts,flooding, tornadoes and rare earthquakes many located in regions not known for seismic activity for 50-150 years.

This past week alone reports have been flowing in from worried residents throughout Oklahoma,Georgia,Tennessee,& Texas.The residents reported they heard loud booming sounds while the earth beneath them rattled around. Radar tracking captured birds or bugs fleeing on as the tremors occurred.Are these tremors the result caused by seismic waves ? You ask what are seismic waves ?

Seismic waves are waves of energy that travel through the earth, 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. Seismic waves are studied by seismologists and geophysicists. Seismic wave fields are measured by a seismograph, geophone, hydrophone (in water), or accelerometer.

The propagation velocity of the waves depends on density and elasticity of the medium. Velocity tends to increase with depth, and ranges from approximately 2 to 8 km/s in the Earth’s crust up to 13 km/s in the deep mantle.

Earthquakes create various types of waves with different velocities; when reaching seismic observatories, their different travel time enables the scientists to locate the epicenter. In geophysics the refraction or reflection of seismic waves is used for research of the Earth’s interior, and artificial vibrations to investigate subsurface structures.

There are two types of seismic waves, body wave and surface waves. Other modes of wave propagation exist than those described in this article, but they are of comparatively minor importance for earth-borne waves, although they are important in the case of asteroseismology, especially helioseismologyy.

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