- Early civilizations, without the benefits of modern science, came up with myths to explain why the ground shook violently every so often. In Japan, it was said a giant Catfish called Namazu caused them when the god responsible for restraining him let his guard down. Norse mythology says earthquakes happen because trickster god Loki was imprisoned in a cave with a snake dripping venom over him. Loki's wife catches most of the venom in a bowl but when the bowl is full and she has to empty it, a drip of poison lands on Loki's face and he thrashes about in pain. In Greece, earthquakes happened because the god Poseidon was in a bad mood. In Hindu mythology, Earth is held in place by eight gigantic elephants, all balanced on the back of turtle, which itself stands on the coils of a snake. If any of these creatures move, it causes an earthquake.
- Time passes, and Greek philosophers began to look for more scientific explanations. Tensions between air and water, water in general, air escaping from underground caves, and underground thunderstorms were among the theories they came up with.
- Today, we know that most earthquakes are caused by movements of the earth's tectonic plates, although some human activity can cause them as well, such as mining, drilling, building, build up of water behind dams, and nuclear testing.
- Some Earthquake related words: the study of earthquakes is called seismology and an instrument for measuring them is a seismograph (invented by an Englishman called John Milne in 1880, although a device for detecting them was invented in China 2,000 years ago by a Chinese astronomer named Zhang Heng). The extent to which an area is prone to earthquakes is its seismicity. Where the quake actually occurs is called the “focus” or “hypocentre”. The epicentre is the point above the hypocentre, at ground level. An aftershock is a quake that happens after the main one, caused by the fault plane adjusting to the effects of the first one. They are usually lower in magnitude. If an aftershock occurs which has a greater magnitude than the previous quake, the original main shock will be re-designated as a foreshock.
- The first scale for measuring earthquake magnitudes was developed by Charles F. Richter in 1935. News reports about earthquakes will usually mention what it measured on the Richter Scale. Scientists, however, don't use that scale so much, as it was developed around Southern California and Nevada, and differences in the earth's crust in other places make it inaccurate. They have developed other scales, and the one they are most likely to use now is the moment magnitude scale, based on the actual energy released by an earthquake. Richter influenced subsequent scales, however. Like the Richter Scale they are usually logarithmic, so each unit represents a ten-fold increase in the amplitude of the seismic waves.
- Which places in the world are most prone to earthquakes? 90%, of them, including 81% of the largest, happen in the vicinity of a 40,000 km (25,000 mi) horseshoe shaped chain of oceanic trenches, volcanic arcs, and volcanic belts known as the circum-Pacific belt, or Ring of Fire, in the Pacific Ocean. El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal and Japan are the most earthquake-prone nations. In the USA, while most people associate earthquakes with California, (Parkfield, California, is known as “The Earthquake Capital of the World” and has a bridge that spans two tectonic plates) the most earthquake prone state is actually Alaska. More earthquakes happen in the Northern Hemisphere than in the Southern Hemisphere.
- It is estimated that around 500,000 earthquakes occur each year, but four fifths of them cannot be felt by humans. The earthquake prone places listed above will be experiencing minor tremors virtually all the time. Earthquakes below a magnitude of four wouldn't be felt by most people. Scientists believe animals can detect weaker quakes because they can sense electrical impulses caused by moving rocks. An earthquake is considered major if it measures 7 or above.
- The UK is a low seismicity area, but that doesn't mean we don't get any at all. I am writing this the day after a 4.2 quake in Wales which actually made items in my study shake a couple of hundred miles away in Somerset. No doubt this influenced my choice of subject for today. A magnitude 4 earthquake happens in Britain roughly every two years, a magnitude 5 roughly every 10–20 years, and one of 5.6 or more every 100 years. Research suggests that the largest possible earthquake in the UK would be around 6.5. The largest known British earthquake occurred near the Dogger Bank, 60 miles off shore, in 1931, with a magnitude of 6.1. It caused minor damage to buildings on the east coast. The North Sea is the most active area around the UK. On the mainland, they are most likely to occur in the west, while eastern Scotland, north east England and Ireland hardly ever have earthquakes. The ones we do get in the UK are mostly caused by tectonic plate movement resulting from the melting of the ice from the ice age.
- The earliest recorded earthquake is from 1831 B.C. in the Shandong province in China. The worst ones? An earthquake in A.D. 1201 in the eastern Mediterranean is thought to be the worst earthquake in history - it claimed an estimated one million lives. Since records began, the most devastating was in Shansi, China on January 23, 1556. An estimated 830,000 people died. That wasn't the most powerful earthquake ever recorded, however. That was in Valdivia, Chile in 1960, with a magnitude of 9.5. The next most powerful earthquake ever recorded was the Good Friday earthquake in 1964 in Prince William Sound, Alaska - which released only about half the energy of the one in Chile. On average, an earthquake lasts about a minute. The longest on record was the 2004 Indian Ocean earthquake which lasted nearly 10 minutes. The 9.0 quake that hit Japan in 2011 was pretty bad, too. It created a tsunami with waves as high as 30 feet (10 meters) and a 186-mile long and 93 mile wide rift 15 miles under the ocean. It also moved Japan slightly closer to the United States and shifted the planet’s axis by 6.5 inches. It caused the planet to spin faster and shortening the day by 1.6 microseconds. A quake in Sumatra in 2004 shortened the day by 6.8 microseconds. Earthquakes kill approximately 8,000 people each year.
- Quakes occur on the Moon, too. They are called moonquakes and they are usually weaker than earthquakes.
More details about my books. Follow this link if you like Superheroes, Psychics and/or quirky short stories.
I've listed the themes each novel touches on here for easy reference.
Like my author page on Facebook for news on new books and blog posts.
No comments:
Post a Comment