Earthquakes are some of the most frightening and deadly occurrences in the whole world. A lot of people have died because of them and a lot of destruction have been caused by them.
Read on to find some facts about earthquakes that you didn’t know!
- An earthquake is the shaking of the surface of the Earth
- Eathquakes are the result of the sudden release of energy in the Earth’s lithosphere that creates seismic waves
- Earthquakes can range in size
- They are the weak ones that cannot be felt
- To those violent enough to toss people around and destroy whole cities
- The seismicity, or seismic activity, of an area is the frequency, type and size of earthquakes experienced over a period of time
- Other words for describing earthquakes are quake, tremor or temblor
- The word tremor is also used for non-earthquake seismic rumbling
- At the Earth’s surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground
- When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami
- Earthquakes can also trigger landslides, and occasionally volcanic activity
- In its most general sense, the word earthquake is used to describe any seismic event that generates seismic waves
- Earthquakes are caused mostly by rupture of geological faults
- They are caused also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests
- An earthquake’s point of initial rupture is called its focus or hypocenter
- The epicenter is the point at ground level directly above the hypocenter
- Tectonic earthquakes occur anywhere in the earth
- They are caused by sufficient stored elastic strain energy that drives fracture propagation along a fault plane
- The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional resistance
- Most fault surfaces do have such asperities and this leads to a form of stick-slip behavior
- Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface
- This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy
- This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake
- This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory
- It is estimated that only 10 percent or less of earthquakes’ total energy is radiated as seismic energy
- Most of the earthquakes energy is used to power the earthquake fracture growth or is converted into heat generated by friction
- Earthquakes lower the Earth’s available elastic potential energy and raise its temperature
- Tides may induce some seismicity
- Most earthquakes form part of a sequence, related to each other in terms of location and time
- Most earthquake clusters consist of small tremors that cause little to no damage
- There is a theory that earthquakes can recur in a regular pattern
- Quaking or shaking of the earth is a common phenomenon undoubtedly known to humans from earliest times
- Prior to the development of strong-motion accelerometers that can measure peak ground speed and acceleration directly, the intensity of the earth-shaking was estimated on the basis of the observed effects, as categorized on various seismic intensity scales
- Only in the last century has the source of such shaking been identified as ruptures in the earth’s crust, with the intensity of shaking at any locality dependent not only on the local ground conditions, but also on the strength or magnitude of the rupture, and on its distance
- The first scale for measuring earthquakes was developed by Charles F. Richter in 1935
- Subsequent scales have retained a key feature, where each unit represents a ten-fold difference in the amplitude of the ground shaking, and a 32-fold difference in energy
- Subsequent scales are also adjusted to have approximately the same numeric value within the limits of the scale
- Although the mass media commonly reports earthquake magnitudes as “Richter magnitude” or “Richter scale”
- Standard practice by most seismological authorities is to express earthquakes strength on the moment magnitude scale
- It is estimated that around 500,000 earthquakes occur each year
- About 100,000 of these can be felt
- Minor earthquakes occur nearly constantly around the world
- But earthquakes can occur almost anywhere
- Larger earthquakes occur less frequently
- The number of seismic stations has increased from about 350 in 1931 to many thousands today
- As a result, many more earthquakes are reported than in the past
- Τhis is also because of the vast improvement in instrumentation, rather than an increase in the number of earthquakes
- Most of the world’s earthquakes (90%, and 81% of the largest) take place in the 40,000-kilometre (25,000 mi) long, horseshoe-shaped zone called the circum-Pacific seismic belt
- This place is also known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate
- Massive earthquakes tend to occur along other plate boundaries, too
- In areas of high seismic risk, seismologists are warning that a single quake may claim the lives of up to three million people
- While most earthquakes are caused by movement of the Earth’s tectonic plates, human activity can also produce earthquakes
- Four main activities contribute to this phenomenon: storing large amounts of water behind a dam (and possibly building an extremely heavy building), drilling and injecting liquid into wells, and by coal mining and oil drilling
- Perhaps the best known example is the 2008 Sichuan earthquake in China’s Sichuan Province in May
- This tremor resulted in 69,227 fatalities and is the 19th deadliest earthquake of all time
- The greatest earthquake in Australia’s history is also claimed to be induced by human activity
- The instrumental scales used to describe the size of an earthquake began with the Richter magnitude scale in the 1930s
- It is a relatively simple measurement of an event’s amplitude, and its use has become minimal in the 21st century
- Seismic waves travel through the Earth’s interior and can be recorded by seismometers at great distances
- The surface wave magnitude was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events
- The moment magnitude scale measures the amplitude of the shock, but also takes into account the seismic moment
- The Japan Meteorological Agency seismic intensity scale, the Medvedev–Sponheuer–Karnik scale, and the Mercalli intensity scale are based on the observed effects and are related to the intensity of shaking
- Every tremor produces different types of seismic waves, which travel through rock with different velocities
- The effects of earthquakes include, but are not limited to, the following shaking and ground rupture, landslide, fires. soil liquefaction, tsunami and floods
- One of the most devastating earthquakes in recorded history was the 1556 Shaanxi earthquake, which occurred on 23 January 1556 in Shaanxi province, China
- This earthquake cause the death of more than 830,000 people died
- The 1960 Chilean earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960
- Its epicenter was near Cañete, Chile
- The next most powerful earthquake, the Good Friday earthquake (March 27, 1964) which was centered in Prince William Sound, Alaska
- The ten largest recorded earthquakes have all been megathrust earthquakes
- However, of these ten, only the 2004 Indian Ocean earthquake is simultaneously one of the deadliest earthquakes in history
- There is a whole science developed on the prerarednes for the earthquakes
- The objective of earthquake engineering is to foresee the impact of earthquakes on buildings and other structures and to design such structures to minimize the risk of damage
- Existing structures can be modified by seismic retrofitting to improve their resistance to earthquakes
- Earthquakes insurance can provide building owners with financial protection against losses resulting from earthquakes
- Emergency management strategies can be employed by a government or organization to mitigate risks and prepare for consequences
- From the lifetime of the Greek philosopher Anaxagoras in the 5th century BCE to the 14th century CE, earthquakes were usually attributed to “air (vapors) in the cavities of the Earth.”
- Thales of Miletus (625–547 BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water
- Other theories existed, including the Greek philosopher Anaxamines’ (585–526 BCE) beliefs that short incline episodes of dryness and wetness caused seismic activity
- The Greek philosopher Democritus (460–371 BCE) blamed water in general for earthquakes
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