mysterious hollow earth

Discover Gaïa most hidden secret

How do scientists map the earth's interior?

Recordings of seismic waves from earthquakes led to the discovery of the earth's core and eventual maps of the layers of the Earth's inside.



Just as the prism (in the video below) refracts light at its faces

Seismic waves bend, reflect and change speed at the boundaries between different materials below the Earth's surface.

Earthquakes generate three types of seismic waves: P (primary) waves, S (secondary) waves and surface waves, which arrive at seismic recording stations one after another.


Both P and S waves penetrate the interior of the Earth while surface waves do not. Due to this, P and S waves are known as "body waves". Surface waves arrive last and are the least interesting to seismic tomographers because they don't penetrate deep inside the Earth, therfore provide little information about inacessible terrain.

The major differences between P and S waves


P WAVES


  • compressional wave
  • longitudinal wave
  • first to arrive at seismic stations
  • travel speed from 1.5 to 8 km/sec. in the earth's crust
  • shake the ground in the direction they are propagating
  • travel through the earth's core
S WAVES

  • shear waves
  • second to arrive at seismic stations
  • 1.7 times slower than P waves
  • shake the ground perpendicular to the direction in which they are propagating
  • do not travel through gaseous medium & liquid (water, molten rock, the earth's outer core)

Decades ago, seismologists noticed that records from an earthquake changed once the event was a certain distance away, aproximately 105 degrees in terms of the angle between the quake and the seismograph at the center of the Earth.


After such a distance, waves disappeared almost completely until the slow surface waves arrived. The area beyond 105 degrees forms what is called a SHADOW ZONE.


At greater distances some P waves would arrive but no S waves. From this, researchers determined the Earth's core is fluid and molten _could it rather be a gaseous medium?_

S waves do not travel further since they can not spread through liquid & gaseous medium as for the P waves, they  travel at a speed comprised between 1.5 to 8 km/sec. ; 1.5 km/sec. is the speed at which sound waves travel through water therefore, if P waves were travelling through a gaseous medium they should travel roughly at a speed of 330 meters/sec. "the speed changes as well with the temperature and the density of the gaseous medium "...



This explains the lack of S waves in the shadow zone and the bending of P waves to form their own shadow zone.


This is just one example of how seismic tomographers used data concerning seismic waves to map the Earth's inside.

There is an excerpt of the site of David Pratt concerning the hollow earth hypothesis :

 If the force of gravity on both the outer and inner surfaces of the earth's solid shell is directed 'downward', i.e. into the shell, there must be a zone of zero gravity somewhere within the shell, where these two forces cancel. Etidorhpa places this 'energy shell' or 'sphere of rest' at a depth seven eighths of the distance from the outer to the inner surface. Such a zone might reflect S waves and most P waves. Some of the P waves that pass through it, or perhaps the vast majority, might then be channelled around the earth between the inner surface and the energy sphere, with most of them being refocused on the other side of the earth, thereby creating the P-wave shadow zones. In this model, rather than P waves travelling more slowly through the 'outer core' than through the mantle, most may not travel through the cavity at all but make a detour around it, so that their slower speed is only apparent. However, if virtually no P waves travel through the cavity, some explanation other than a central sun would be needed to account for the seismic data that suggest an 'inner core'.