An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock . Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the main shock. Most aftershocks are located over the full area of fault rupture and either occur along the fault plane itself or along other faults within the volume affected by the strain associated with the main shock. Typically, aftershocks are found up to a distance equal to the rupture length away from the fault plane. The pattern of aftershocks helps confirm the size of area that slipped during the main shock. Aftershocks are dangerous because they are usually unpredictable, can be of a large magnitude, and can collapse buildings that are damaged from the main shock. Bigger earthquakes have more and larger aftershocks and the sequences can last for years or even longer especially when a large event occurs in a seismically quiet area.
4. Earthquake Swarms
Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time. They are differentiated from earthquakes succeeded by a series of aftershocks by the observation that no single earthquake in the sequence is obviously the main shock. Earthquake swarms are one of the events typically preceding eruptions of volcanoes. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park.
3. Earthquake Storms
An earthquake storm is a recently proposed theory about earthquakes, where one triggers a series of other large earthquakes—along the same plate boundary—as the stress transfers along the fault system. This is similar to the idea of aftershocks, with the exception that they take place years apart. These series of earthquakes can devastate entire countries or geographical regions. Possible events may have occurred during the end of the Bronze Age, and the latter part of the Roman Empire. It has been suggested that this is what may be occurring in modern day Turkey.
2. Earthquake in Mythology and Religion
In Norse mythology , earthquakes were explained as the violent struggling of the god Loki. When Loki, god of mischief and strife, murdered Baldr, god of beauty and light, he was punished by being bound in a cave with a poisonous serpent placed above his head dripping venom. Loki’s wife Sigyn stood by him with a bowl to catch the poison, but whenever she had to empty the bowl the poison dripped on Loki’s face, forcing him to jerk his head away and thrash against his bonds, which caused the earth to tremble. In Greek mythology , Poseidon was the cause and god of earthquakes. When he was in a bad mood, he struck the ground with a trident, causing earthquakes and other calamities. He also used earthquakes to punish and inflict fear upon people as revenge. In Japanese mythology , Namazu is a giant catfish who causes earthquakes. Namazu lives in the mud beneath the earth, and is guarded by the god Kashima who restrains the fish with a stone. When Kashima lets his guard fall, Namazu thrashes about, causing violent earthquakes.
Thales of Miletus , who lived from 625-547 (BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water.
1. Animals can predict Quakes!
In April 2009, British researchers were studying the common toad at a breeding site in central Italy when they “observed a mass exodus of toads,” Jill Lawless reports for the Associated Press. Just five days later, a 6.3-magnitude earthquake hit, killing some 150 people and causing extensive damage to the town of L’Aquila. Rachel Grant, a researcher at Open University and lead author of one of the first studies to document animal behavior surrounding earthquakes, believes “that toads are able to detect pre-seismic cues such as the release of gases and charged particles, and use these as a form of earthquake early warning system.” According to the study, “Predicting the unpredictable; evidence of pre-seismic anticipatory behaviour in the common toad,” the toad population at the breeding site dropped to zero three days prior to the quake. “A day after the earthquake, they all started coming back,” Grant told the AP. “The numbers were still lower than normal and remained low until after the last aftershock.” The belief that animals can predict earthquakes has been around for centuries,” Maryann Mott wrote for National Geographic News in 2003. In 373 B.C., historians wrote that rats, weasels and snakes made a mass exodus from the Greek city of Helice days before an earthquake destroyed the city. Other examples exist from throughout the centuries. Reports include bees leaving their hive, catfish moving violently and chickens refusing to lay eggs. Pet owners also have examples of their cats and dogs behaving strangely before a quake. To date, seismologists can’t predict when or where the next earthquake will hit, and scientists don’t know what, if anything, animals sense before a quake. Some, like Grant, think they can detect changes in the Earth’s gases. Others wonder if animals’ more sensitive hearing and other senses allow them to feel vibrations that humans can’t, or detect electrical changes. Whatsoever the exact mechanism but the fact is that they feel it and flee.