The Worlds Riskiest Places for Earthquakes
An Earthquake is one of the most devastating and destructive natural phenomenon that anyone can ever encounter. Earthquakes have in the recent past caused destruction in countries like Japan, Turkey and Iran, but some of the worst Earthquakes have happened in China in the early 20th century, like the 1920, 1927 and 1976 Chinese earthquakes that each killed over 200,000 people. The recent earthquake in China’s Sichuan province killed over 69,000 people mostly school children but the worst earthquake in China’s history was the 1976 earthquake which killed 650,000 people.
To understand how earthquakes occur one first requires to understand plate tectonics. Plate tectonics posits that the earth’s crust is made up of a series of rigid plates which float on a soft layer of mantle and are moved about by convection currents in the earths interior. These plates converge and diverge along margins marked by earthquakes, volcanoes and other seismic activity.
These plates diverge from mid-ocean ridges where molten lava pushes upwards and forces the plates apart at rate of up to 3 centimeter a year.
Converging plates from either a trench, where the oceanic plate sinks below the lighter continental rock or mountain ranges where two continents collide.
The earth’s surface is therefore slowly but surely being rearranged. This constant state of flux is what causes earthquakes. According to the Philips Modern Atlas, earthquakes are described as a series of rapid vibrations originating from the slipping or faulting of parts of the earths crust when stresses within it build up to breaking point. They usually happen at depths of between 8 to 30 kilometers and are also known as the epicenter.
Seismic waves are shock waves sent out from the epicenter of an earthquake, there are three main types of waves each with distinct characteristics. Primary (P) waves that are compressional in nature they can be transmitted through both solids and liquids and as such they pass through the Earth’s core. Secondary(S) waves are shear waves and they can only pass through solids they therefore cannot pass through the Earth’s core. The third main kind of wave is a long (L) wave; a slow wave that travels along the earth’s surface its motion is either horizontal or vertical.
The riskiest place for earthquakes on our planet is along what is known as the Pacific Ring of Fire, where the Pacific plate collides with the North American Plate. The Western seaboard of the US falls within this area with the San Andreas Fault cutting through San Francisco and most of California. Historically the heaviest loss of life has occurred when quakes with a magnitude of 7.0 or more on the Richter scale or more hit densely populated urban areas. The 1906 San Francisco virtually flattened the city taking with it 700 lives.
The quake measuring 7.4 on the Richter scale that struck the Turkish City of Izmit on July 27, 1999 claimed more than 45,000 lives. The quake occurred on the North Anatolian Fault, a thin zone of quake-prone crushed rock near three great plates on the Earth’s crust. It was a strike-slip earthquake this particular earthquake occurs when the blocks of crust move slipping past each other horizontally. But now better understanding by seismologists, the people responsible for studying earthquakes, is mitigating the effects of earthquakes by recommending the building of structures that limit earthquake damage or the construction of earthquake proof buildings.