Seismic waves, which 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. There are two types of seismic waves, Body waves and surface waves.
Body waves travel through the interior of the earth. Surface waves travel along the earth’s surface and through water. Seismic wave fields are measured by a seismograph, geophone, hydrophone or accelerometer. These are used to measure earthquakes.
When measuring these earthquakes these seismic waves are broken down into Primary and secondary waves.Primary waves (P-waves) are compressional waves that are longitudinal in nature. Secondary waves (S-waves) are shear waves that are transverse in nature. The biggest difference between P and S waves is their velocity. P-waves travel more quickly than S-waves. P-waves can travel through solids, liquids and gasses. S-waves can only travel through solids.
The method used to determine the distance from a location to the origin of a seismic wave less than 200 km away is to take the difference in arrival time of the P wave and the S wave in seconds and multiply by 8 kilometers per second.This method varies depending on how far the origin of the wave is. Using these different methods many different things can be found/ discovered. The exploration of the earth’s structure has been made possible due to some of these studies. We now have data to measure the depth of the earth’s core.
One of these discoveries is that the earth’s core is liquid. This knowledge is based on the behavior of seismic waves, particularly the behavior of P-waves and S-waves. S-waves are unable to travel through liquids, and this particular wave trait indicates a boundary between the solid mantle and the liquid outer core.The boundary between the inner core and outer core is also detected by a difference in velocities of P-waves. The Earth’s magnetic field also originates in the liquid outer core by the movement and currents of molten metal in this layer.
Scientific experiments have revealed that with the calculated density of the Earth, despite the incredible temperatures, the inner core should remain solid due to the massive pressures there. It is pretty amazing that all of these things happen within the earth , and they can all be measured without going deep down to find them