As we have seen, most earthquakes are essentially the product of tectonic stresses which are generated at the boundaries of the Earth's tectonic plates. The severity of an earthquake can vary from events which are barely detectable even using the most sophisticated devices, to devastating events which can level cities and trigger Tsunamis and sometimes even volcanic activity. The amplitude (height) of the largest recorded wave of an earthquake at a specific distance is called the Richter magnitude. Tectonic earthquakes can range in size from magnitudes less than zero, resulting from fault slippage of a few centimetres, to the largest events (magnitude greater than 9), where fault displacements are on the order of many metres. There is no limit to the possible magnitude of an earthquake but historically just over magnitude 9 is the record. Richter and Mercalli Earthquake Scales describing earthquake force logarithmically, meaning the energy increases.
The Richter magnitude scale (often shortened to Richter scale) was developed to assign a single number to quantify the energy released during an earthquake. A pen at the top of the device records a zig-zag line on the moving, paper-covered cylinder whenever an earthquake is detected.


Under the Richter scale, each order of magnitude is 10 times more intensive than the last one, which means that a two is 10 times more intense than a one and a three is one hundred times greater. Earthquake size is determined not only by amount of displacement but also area of the ruptured fault plane.
The earthquake of most recent history to reach 9 on the Richter scale was the Japan quake of March 2011. They are very sensitive instruments that can detect, measure and record ground vibrations and their intensities during an earthquake. Various scales were proposed to measure the magnitude of earthquakes until 1935, when the Richter Scale was developed by a seismologist named Conrad Richter to measure the intensity of the seismic waves. But it is to point out that, while it is correct to say that for each increase in 1 in the Richter magnitude there is a tenfold increase in amplitude of the wave, it is incorrect to say that each increase of 1 in Richter magnitude represents a tenfold increase in the size of the earthquake (as is commonly incorrectly stated by the press). The deeper the earthquake, the more powerful it is, but it is also far less likely to reach the surface. The 1906 San Francisco earthquake, with a magnitude of 8.3, was approximately one million times as powerful as the atomic bomb dropped on Hiroshima.


A magnitude 7 earthquake ruptures a fault area of about 1000 km2 or about 50 km long and 20 km wide.
That’s why shallow earthquakes are more common and more dangerous, because the shallower an earthquake, the more damage to surface structures it can cause.
The earthquake triggered tsunami warnings and serious social media chatter, but resulted in little property damage and no known fatalities.
Seismographs can help us determine the time, epicentre, focus, and the type of faulting which produced an earthquake as well as estimate how much energy was released.



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