Haiti, Chile Earthquakes Suggest Increased Frequency: Untrue
Earthquakes, and their related natural phenomena - tsunamis, typhoons and hurricanes - like the ones that devastated Haiti January 12th and Feb 27 struck Chile with a magnitude of 8.8 on the Richter Scale, suggest that the earth is alive in more ways than one.
According to British scientist James Lovelock and his Gaia hypothesis, it may even be conscious. Earthquakes are caused by stress factors due to the movement of the continental plates that swim within the earth's inner layer of magma.
We live on the cooled outer crust, a gigantic raft that floats on a hot, dense ocean. The plates' mass is such that any movement is felt. Because we are small by comparison, we notice these movements in the same manner a microbe may perceive a twitch by its host.
A History of High-Magnitude Quakes
The single most devastating earthquake with respect to casualties happened in Shaanxi, China in the 16th century, killing over 830,000. That earthquake is estimated to have been 8.0 or higher.
Some believe earthquakes are happening more frequently than in the past and use records to prove their point, but this theory is flawed because we have only been keeping accurate global records for a very short time. All records prior to the 20th century where regional and did not monitor earthquakes beyond this locale.
We have only 12 recorded earthquakes above 6.9 in magnitude in the 19th century compared to a 125 in the 20th century. The average number of earthquakes per year in the range above 6.9 in magnitude is 35.
In the last decade, we had 354 earthquakes - of those, 6 measured between 7.0 and 7.9 in magnitude. It is estimated we have had more then 300,000 earthquakes, but most of them were so minor that only a very sensitive seismograph could record them.
Quakes of the order of the Chilean earthquake happen only 2-6 times each century from what we can deduct from recorded data. Records predating the 20th century are not very accurate, but historical references offer some indication as to how strong they may have been.
Geographical Areas Prone to Earthquakes
Some areas prone to earthquakes are more vulnerable because the tectonic plates first formed 4 billion years ago keep shifting beneath them. Our continents were once one large land mass that broke up into the continents we know today.
Europe and Africa move away from the Americas by a measurable distance annually, whereas North America, Asia and Australia are on a collision course, as the attached map of stress factors and tectonic plate movements illustrates.
Japan, the North American west coast, and the Caribbean Islands are more prone to earthquakes than other areas. The last 4 powerful earthquakes occurred where the tectonic plates meet.
The December 26 2004 tsunami in the Indian ocean had its epicentre on the west cost of Sumatra in Indonesia. This tsunami killed nearly 230,000 people with waves as high as 10 metres. The earthquake itself had a magnitude of 9.1 on the Richter’s Scale. The energy released was estimated at 1.1×1017 joules or 26.3 megatons of TNT.
Body and Surface Wave Tsunamis
Tsunami waves are most frequent in the Pacific Ocean because of earthquakes in the "Ring of Fire" and an effective tsunami warning system has long been in place there. The 2004 Tsunami inspired discussions about a warning system throughout the Indian and Atlantic oceans.
Not every earthquake generates a tsunami. On March 28, 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean, but did not result in a major tsunami. Earthquakes always have an epicentre from which the earthquake originates and most start in the ocean. The waves are generated in two distinctive ways - body waves and surface waves.
According to Wikipedia,
“The body waves travel through the interior of the earth. They follow ray paths refracted by the varying density and modulus (stiffness) of the earth's interior. The density and modulus, in turn, vary according to temperature, composition, and phase. This effect is similar to the refraction of light waves. The surface waves on the other hand are analogous to water waves and travel along the earth's surface. They travel more slowly than body waves. Because of their low frequency, long duration, and large amplitude, they can be the most destructive type of seismic wave. There are two types of surface waves: Rayleigh waves and Love waves.”
Those waves travel great distances and when they meet an obstacle, such as a bedrock from a mountain chain, they are bounced like an echo and meet with a second wave or after shock causing a devastating collision of two forces.
This happened on January 17, 1995 at 5:46 iam during the Hanshin earthquake in Japan, which claimed 6300 lives. That earthquake measured 7 on the scale of Japan's Meteorological Agency (JMA), 6.8 on the Moment magnitude scale (USGS), and Mj 7.3 (adjusted from 7.2) on JMA magnitude scale.
All of this is to say that though we may believe earthquakes to be more frequent and more devastating, in fact technology has merely provided us the opportunity to record and respond to them now in ways that quantify their effects with startling visual accuracy. Perhaps we should spend less time isolating ourselves from nature and more time trying to reconnect with it, so we may hear, feel and see what the earth is trying to tell us.