Why do earthquake waves develop shadow zone?
There are two types of body waves which are called P and S waves. The behavior of these two waves is different. Due to this different behavior, we get to know about the internal structure of the earth. Seismic waves are recorded on the seismograph at distant places. But due to some specific property of the seismic wave, there are some areas where the seismic waves are not recorded on the seismograph, these areas are called shadow areas.
image Sc: NCERT
Shadow regions are formed because
- The "P" wave can pass through solid, liquid, and gas, but its speed is different in different mediums. For example, the speed of the "P" wave in the solid medium is maximum; When the "P" wave reaches the outer core (the outer core is fluid), the speed and direction of the wave get changes, due to these reasons the P wave creates a shadow area between 105 degrees to 145 degrees from the earthquake's focus.
- We know that S wave can pass through solid only when S wave reaches the outer core, it cannot pass through the outer core because of its liquid state. It did not reach beyond 105 degrees from the earthquake's focus. It creates more shadow area than a P wave.
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