Though Southern California is considered by many as earthquake central, the United States Geological Survey reports each year there are at least one million quakes recorded throughout the world, with yes, 10,000 in California alone.
What do we know about earthquakes? How were they recorded and regarded in history? Why do they happen and where do they occur most often?
Location, location, location!
Earthquakes occur most along the edge of continental and oceanic plates. According to geoscientists and seismologists, about 80 percent of earthquakes happen around the Pacific Ocean, near Asia’s East Coast and North America’s West Coast.
Did you know that earthquakes, volcanoes, and mountain ranges are related? They are all essentially born of plate tectonics, or large-scale movements of the earth. This can happen when two tectonic plates collide and pull away from one another, or scrape against one another, or when one plate is thrust under the other. The surface where they slip is called the fault or fault plane. Ranges form as magma (molten or semi-molten rocks) rises up. According to the USGS, the study of plate tectonics tells us the Earth’s lithosphere (an uncompromising outer shell) is broken up into a mosaic of oceanic and continental plates, which can slide over the uppermost layer of the mantle, or asthenosphere – which lies just below the lithosphere. As a result of this movement, earthquakes occur, volcanoes are born, and mountain ranges are formed.
Are there quakes on the moon? Indeed there are, though they happen less frequently and occur at greater depth: about halfway between the center and surface of the moon.
At the center
What’s the difference between an epicenter and a hypocenter? The hypocenter – from the Greek, meaning below the center – is the underground focal point of an earthquake. It’s where the energy stored in the rock is first released, occurring directly beneath the epicenter. The epicenter is the point where an earthquake originates – directly above where a fault begins to rupture and usually the site of the greatest damage.
In California, land of ubiquitous backyard swimming pools, a standing wave, or seiche (Swiss French for “sway back and forth”), is a common occurrence following an earthquake. Generally wind, atmospheric pressure variations or an earthquake can cause a seiche, which is essentially a standing wave in a body of water that is partly bounded. In this case, it is contained by the swimming pool’s walls.
In ancient times, it was a sure bet that inhabitants of Damghan, Iran (856 A.D. earthquake later evaluated at about 7.9 that caused 200,000 fatalities), Antioch, Greece (526 A.D. quake that killed 250,000) and other civilizations thought these earthly catastrophes were the result of angry gods. Depending on their persuasion, all manner of assuagement was offered up, including animal and human sacrifices. As if the direct loss of life from the natural disaster wasn’t enough, a succession of aftershocks could seriously diminish the mammalian population.
Dr. Richter, I presume
American seismologist Charles F. Richter of the California Institute of Technology invented the Richter Scale in 1935. It determines the amount of energy an earthquake releases by measuring magnitude or seismic waves.
Scientists and anyone who has experienced an earthquake can tell you that there are few (or no) surefire ways to get ready for the possibility of an earthquake. Depending on its magnitude, no amount of preparation may be able to prevent a lot of injury and destruction.
Safety ideas, however, include using Velcro to help fine china adhere to shelves and placing heavier objects on lower shelves. Pictures and mirrors should never be hung directly over a bed or seating area. Water heaters can be strapped to studs in the wall and bolted to the floor.
Pesticides and flammable products should be stored on bottom shelves and even locked into cabinets. Find out how to shut off gas, electricity, and water. Practice taking cover under heavy furniture, in a door jamb, or flush against a wall with head turned towards it and hands overhead – away from breaking glass and flying debris.