An earthquake occurs due to a sudden release of energy in Earth’s lithosphere. Seismic waves are in fact, the vibrations that carry this energy from the source outwards in all directions.
Waves produced by a stone thrown on the surface of water could be a good visualization of an earthquake. However, seismic waves generated due to an earthquake are way more complicated. An earthquake radiates two types of waves i.e. compressional (Primary) and transverse (Secondary). The P and S waves interact with the surface of the earth to produce surface waves.
Intuitively, a seismic wave generated in one part of the globe will travel throughout it. But does it move fast enough to be felt by people in the other part?
Seismic waves travel at great speed. The rate of the P waves varies between 1-14 km/s depending on some factors, particularly the rock composition. Temperature and pressure also significantly alter the speed of seismic waves. An increase in temperature tends to lower the speed of seismic waves whereas more pressure tends to move these waves faster. The rise in pressure plays a more significant role than that of temperature; therefore, the wave velocity is higher at greater depths.
The S waves travel at speed lower than that of P waves. The difference between the arrival time of S and P waves at a seismograph helps to calculate the location of the earthquake.
The diameter of the earth is almost 12,742 km. The speed of the seismic waves varies between 1-14 km/s with different rock composition and depth. If we consider an average wave velocity of 7km/s, it will take nearly 30 minutes for an earthquake to travel to the other side of the globe.
Humans can not feel a tremor of 3.0 Hz and below on a Richter scale. While the seismic waves are traveling to the other side of the Earth; there will be a significant reduction in their intensity. So, even though the waves will travel throughout the Earth; yet, the people residing on the opposite end of the globe will not feel these waves, unless the earthquake was strong enough to destroy the entire continent.
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