Earthquakes, one of the most destructive natural phenomena, consist of rapid vibrations of rock near the earth’s surface. Because of their unpredictable occurrence and enormous capacity of destruction, they have brought fear to mankind since ancient times. A single shock usually lasts no more than a few seconds, but a series of smaller quakes may last for as long as five minutes. The quake felt on the surface is always the result, not the cause of some underground geologic process, and in many cases the damage done is immense.
The Greek word for shaking, and (when applied to the earth) earthquake, is seismos. Therefore, the science of earthquakes is called seismology (World Book Dictionary 1985). Earthquakes have been recorded as early as 526 A.C., but seismology is comparatively new. Until the 18th century, few accurate descriptions of earthquakes were recorded, and little was known about what caused them. When seismology was introduced it was learned that many earthquakes are the result of sea floor spreading, but most are caused by volcanic eruptions and plate tectonics. The plate tectonic theory explains that the earth is made up of 20 different plates that are always moving slowly past each other. This action pulls and compacts the plates, creating intense forces that cause the plates to break. This, in turn, causes earthquakes. The energy released then travels along fault lines in seismic waves (World Book Encyclopedia).
Seismic waves are either P-waves (primary), or S-waves (secondary). P-waves create a relatively low wave train and arrive at the surface first. On the surface they create a push-pull effect, thus moving the surface up and down. Their low amplitude and vertical movement create an effect much like a dangling slinky. S-waves arrive second and are much more damaging. The high amplitude of S-waves, combined with their horizontal movement cause crippling effects on the earth’s surface and man made structures (Watkins, Bottino, and Morisawa 30-32).
Earthquakes occur around us all the time. Most are too small to notice and cause little to no damage. However, every so often large earthquakes do occur. Large earthquakes leave catastrophic damage and have brought death tolls up to 850,000 (World Book Encyclopedia). The majority of death and destruction is the effect of the secondary shocks. Fires, landslides, tsunami, falling rock, damaged buildings, and damaged gas lines are just a few results of secondary shocks. These conditions reek havoc on earthquake corrupted areas, and in 1934, Bihar-Nepal witnessed this first hand. During a landslide, “…an observer reported that his car sank to the axles”. In 1946 off the coast of the Aleutians, the base of a lighthouse ended up 45 feet below sea level after a tsunami wave over 100 feet crashed on shore (Watkins, Bottino, Morisawa 51, 53-54).
An earthquake is a natural occurrence; a phenomena just like rain. They have occurred for billions of years and descriptions as old as recorded history shows their effects on people’s lives. Long before scientific explanations mankind created folklore to explain them. We have come a long way for spinning yarns around the campfire, but there is still no way to prevent earthquakes. All in all it doesn’t hurt to learn as much as one can, but just like taxes and pokemon earthquakes are something we have to live with.
“Earthquake” World Book Encyclopedia. Vol. 6. 1987.
“Seismos.” World Book Dictionary. Vol. L-Z. Ed. Barnhart, Clarence L., and RobertK. Barnhart. 1987
Watkins, Joel s., Michael L. Bottino, and Marie Morisawa. Our Geological Environment.Philadelphia: W.B. Saunders Company, 1975.