P Wave

The P wave is also known as the pressure wave or primary wave. It is a kind of elastic body wave known as seismic waves. The P wave moves faster as compared to seismic waves. They are the first signal that we get when an earthquake arrives at the affected location. They can transmit via solids, liquids, and gases.

p wave

Introduction to the P wave

We refer to it as a primary wave and is of high velocity. It forms from alternating rarefactions and compressions.  Further, it is the primary wave that records in the seismograph.  Other ways are S waves or secondary waves that reach after P waves.  The S waves are slower and the average speed is 65 percent of P waves.  In this article, we are discussing in detail P waves.

The P waves travel on the Earth. The behavior of P waves is analyzed to probe the Earth’s structure.  The difference in velocity indicates the changes in composition or phase.

P-wave Shadow Zone

Whatever information is available on Earth’s structure derives from analysis of travel times, refractions, reflections, and phase transitions of seismic body waves. The p ways transmit via the Earth’s interior fluid layers. The waves refract while passing through the transition between the liquid outer core and semisolid mantle. So, the shadow zone of the P wave is between 142 and 103 degrees.

Properties of the P wave

  1. It is the first wave that is recorded in seismograph at the time of the earthquake
  2. These are compression waves.
  3. It can move through liquids and solids and gas easily.
  4. They shake medium in direction of propagation
  5. In the homogeneous and isotropic solids, the P wave moves in a straight line.

The Velocity of the P wave 

P waves are similar to sound waves in their method of traveling. P waves can easily propagate through stone, air, and water without resulting in any fractional change of velocity. However since P waves generate a certain amount of pressure as they travel, there will be a slight shift in the position of the object or state of matter the P wave is passing through.

Another important aspect about P waves is that the velocity of S waves tends to increase as the depth of the mantle increases. This happens due to the constant increasing Pressure and density. However, surprisingly the recorded waves at a gradually deeper depth tend to move slower. This was noted based on the theoretical calculation which stated the time required to reach a depth of 100 km was lesser as compared to that of 250 km below the surface.

The substances in solid vibrate with the axis of direction of motion of wave energy. The P wave velocity in the earthquake is The velocity 5 – 8 Km/s. The speed varies as per the Earth’s interior region. It is less than 6 Km/s in the crust to 13.5 Km/s in the lower mantle and 11 Km/s in the inner core.

Hence, P waves are primary waves that are compressional and longitudinal. They travel around 1.8 times faster as compared to secondary waves. They can take the kind of sound waves in the air and can travel at the speed of sound waves. However, the average speeds are 334 M/s in the air. The speed of the p wave is around 1455 m/s in water and 5001m/s in granite.

FAQ on P Wave

Question 1: Can Humans feel the P wave?

Answer 1: Pressure waves travel through the earth at various speeds. The P wave, also the Primary wave, is the fastest wave. Due to its high speed, one can feel a jolt like the sensation when the wave arrives within close proximity to the human body.

Question 2: What does an abnormal P wave indicate?

Answer 2: P-wave abnormality in an ECG indicates a clear presence of block or enlargement. Generally at the sinusoidal node one can see Atrial depolarization in such a scenario. In case of normal ECG wave depolarization occurs in the right atrium followed by the left. However, in Atrial enlargement, the pattern is completely missing.

Question 3: What is the difference between P waves and S waves?

Answer 3: P wave can travel through all the 3 states of matter. However, S waves can only travel through a solid-state. On reaching liquid or gaseous state the S waves stop proceeding.

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