An enumeration district is a geographic area determined for purposes of taking the census. In one city there may be many enumeration districts, so once you enter a city, county, or state, you can narrow your results by entering street level information, or investigate enumeration district maps, or descriptions.
P wave. 1. a longitudinal earthquake wave that travels through the interior of the earth and is usually the first conspicuous wave to be recorded by a seismograph. Also called primary wave. Compare L wave, S wave. The P wave is admitted to be the wave of auricular contraction. p wave.
S waves are transverse waves which involve movement of the ground perpendicular to the velocity of propagation. They travel only through solids, and the absence of detected S waves at large distances from earthquakes was the first indication that the Earth has a liquid core. S waves travel typically 60% of the speed of P waves. They are typically more damaging than the P waves because they are several times higher in amplitude.