We hear about earthquakes all over the world. Are they all the same or are there differences? The answer is that there can be a great deal of difference between one earthquake and another. So, what are these differences? Keep reading, and you will find examples of different types of earthquakes, and how they are different.
What is an earthquake? According to the USGS, an earthquake is when two blocks of earth, without notice, start sliding by each other, causing the ground to move. What causes an earthquake? When the pieces of the earth’s outer crust, the tectonic plates, start moving, especially towards each other, in what is known as a convergent fault, the pressures between the two tectonic plates build up, and are released in what we call an earthquake (Wald, 2012). These earthquakes come in many forms, and can do much damage, depending on how much the earth shakes, how deep underground the hypocenter is, and what kind of fault is releasing the energy.
If we were to compare the earthquakes in Sichuan, China in May 2008, Chile in February 2010, and Indiana in December 2010, we would find some similarities, and many differences.
The quake that hit Sichuan on 12 May 2008 had a massive M7.9 magnitude (USGS, 2013), rocking the province and causing massive property damage and loss of life, including the death of some 69,000 people, 18,000 missing, and 5 million left homeless, as well as causing an economic loss estimated at over 86 billion U.S. dollars, with the loss of over 5 million buildings, and damage to another 21 million buildings as well as other things including roadways, dams and pipelines. This earthquake was felt in over ten provinces throughout that region of China (USGS, 2013).
Compare this to the earthquake off the Pacific coast of the town of Maule, Chile on 27 February 2010, about 330 kilometers south of the capital of Santiago. This quake had a higher magnitude, of M8.8 (USGS, 2013), but caused only a fraction of the loss of life and economic loss that happened in Sichuan, China, with only 523 people killed, only 24 missing, and an economic loss of 30 billion U.S. dollars with the loss of some 374,000 structures and another 4,000 boats (USGS, 2013). The reason that the loss of life and property was less in Chile than it was in China was twofold: first, the population density was less in Chile than that of the Sichuan province in China, so there were less eople to be harmed by this earthquake; secondly, the building codes in Chile required that buildings be built to withstand earthquakes pressures, resulting in less property damage and loss of life.
Both of these earthquakes resulted from built-up pressures on fault lines between two tectonic plates, the quake in China resulting from the convergence of the India plate and Eurasian continental plates, and the quake in Chile resulting from the convergence of the Nazca oceanic plate and the South American continental plate and consequent subduction of the oceanic plate underneath the continental plate. The earthquake in China happened thousands of kilometers inland at the conjunction of the elevated Tibetan plateau and the lower Sichuan Basin in south-central China, in hilly terrain, causing numerous landslides (USGS, 2013), whereas the earthquake in Chile happened right off the coast in the Pacific Ocean, and triggered a tsunami that spread across the Pacific Ocean, and whose waves could be spotted and measured hours later in nations around the Pacific Rim, including Mexico, Canada, Alaska, Japan, Hawaii, numerous Polynesian islands, New Zealand, and Papua New Guinea (USGS, 2013). There is the possibility that the Sichuan earthquake was man-made, due to the build up of weight on the earth’s crust from the water in the reservoir behind the nearby Zipingdu Dam, causing stresses that were released in the earthquake (Wade, 2012), but this is only a hypothesis.
The earthquake in north-central Indiana, on 30 December 2010, on the other hand, was minor, being only a M3.8 magnitude (USGS, 2012), resulting in little or no damage, and no loss of life. Whereas the earthquakes in China and Chile occurred on a fault line, the quake in Indiana was not near a fault zone, but was an intraplate event, leading many to believe that perhaps this quake had more to do with a build-up of fluid pressure under the dilatancy-diffusion model (Don Anderson, 1973) hypothesis of earthquakes. The nature of this Midwestern earthquake may be the reason why it was such a minor event.
So, why were these earthquakes, and their effects, so different from one another? The location and nearness of fault lines, and types of tectonic plates they separated, had much to do what made these events different, as well as the level of population, and preparedness of each society to deal with these events, with strategies such as building codes. That is why these events were different.
Bibliography
- Don Anderson, J. W. (1973). The Dilatancy-Diffusion Model of Earthquake Prediction. Proceedings of the Conference on Tectonic Problems of the San Andreas Fault System (pp. 417-426). Stanford, CA: Geological Sciences.
- USGS. (2012, November 7). Magnitude 3.8 – INDIANA – Earthquake Details. Retrieved March 6, 2013, from United States Geological Survey: http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0000x03.php
- USGS. (2013, January 28). Magnitude 7.9 – EASTERN SICHUAN, CHINA – Earthquake Details. Retrieved March 6, 2013, from United States Geological Survey: http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/us2008ryan.php
- USGS. (2013, February 6). Magnitude 8.8 – OFFSHORE BIO-BIO, CHILE – Earthquake Details. Retrieved March 6, 2013, from United States Geological Survey: http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010tfan/
- Wade, S. (2012, December 13). 2008 Sichuan Earthquake Likely Man-Made . Retrieved March 6, 2013, from China Digital Times: http://chinadigitaltimes.net/2012/12/2008-sichuan-earthquake-likely-man-made/
- Wald, L. (2012, July 12). The Science of Earthquakes. Retrieved March 6, 2013, from United States Geological Survey: http://earthquake.usgs.gov/learn/kids/eqscience.php
