P-waves. P-waves, also known as primary waves or pressure waves, travel at the greatest velocity through the Earth. Because of their speed, they are the first waves to be recorded by a seismograph during an earthquake.

P waves are also known as compressional waves, because of the pushing and pulling they do. Subjected to a P wave, particles move in the same direction that the the wave is moving in, which is the direction that the energy is traveling in, and is sometimes called the ‘direction of wave propagation’.

Types

• Body waves travel through the interior of the Earth.
• Surface waves travel across the surface. Surface waves decay more slowly with distance than body waves which travel in three dimensions.
• Particle motion of surface waves is larger than that of body waves, so surface waves tend to cause more damage.

P waves travel fastest and are the first to arrive from the earthquake. In S or shear waves, rock oscillates perpendicular to the direction of wave propagation. The different S waves arrive after the P waves. The slowest (and latest to arrive on seismograms) are surface waves, such as the L wave.

Most mobile operators use from radiofrequency waves in the range up 300 MHz to 3 GHz that can be harmful for human health (1).

No known health effects are expected if your exposure to EMF falls below the levels in the following guidelines: natural electromagnetic fields (like those created by the sun): 200 V/m. power mains (not close to power lines): 100 V/m. power mains (close to power lines): 10,000 V/m. electric trains and trams: 300 V/m.

“There is no known mechanism by which magnetic fields of the type generated by high voltage power lines can play a role in cancer development. Nevertheless, epidemiologic research has rather consistently found associations between residential magnetic field exposure and cancer.”

Magnetic fields for occupational exposures should be limited to less than 0.5 mT (5 gauss or 5,000 mG).

The 5 gauss line is the safety line drawn around the perimeter of the main magnet of the MRI scanner, specifying the distance at which the stray magnetic field is equivalent to 5 gauss (0.5 mT). Five gauss and below are considered ‘safe’ levels of static magnetic field exposure for the general public.

In its guidelines update in 2010, ICNIRP recommends a residential magnetic field exposure limit of 2,000 milligauss (mG) and an occupational exposure limit of 10,000 mG .

In a study that measured EMF in almost 1000 homes in the United States, 50% had average EMF levels of 0.6 mG or less, and 95% had average EMF levels below 3 mG. Keep in mind that these are average EMF levels within a home.