Published on May 19th, 2011 | by Yellow Magpie1
Devastating Mechanisms Behind Earthquakes And Building Safeguards
Earthquakes are one of the most devastating forces of nature. They can occur virtually anywhere on the planet but some locations are much more vulnerable than others. With more than half a million earthquakes occurring annually, roughly one/fifth of these can be felt by humans. Earthquakes are a much more common phenomenon than people generally imagine.
According to the United States Geological Survey, there are approximately 100 earthquakes a year that are large enough to cause damage.
In Yellow Magpie’s Earthquakes: The Deadliest Of All Shockwaves, we briefly looked at the mechanisms of earthquakes . Here we will take a much closer look at shockwaves. We shall also examine why some buildings cope better than others with earthquakes and why some poorly constructed buildings still managed to remain intact.
They are three main types of shockwave that are associated with earthquakes. They are P-Waves, S-Waves and L-Waves. All earthquakes occur where there is movement between massive plates of rock. As the plates rub off one-another, three different types of shockwaves are formed. Each one behaves differently but only one causes destruction.
The first wave to form is called a P-Wave which is short for primary wave. Primary waves are the first waves formed by the Earthquake. They are also the fastest. P-Waves are created by either push or pull dynamics. In other words, the rock plates moving either towards or away from one another will create P-Waves.
These types of shockwaves travel down deep into the Earth and fortunately do not cause much damage.
Secondary waves or S-Waves are caused by the side-to-side impacts of the rock plates. They have a distinct S-shaped or snake-like pattern. They are the second fastest type of shockwave produced by Earthquakes but they too, like P-Waves, travel down into the surface of the Earth. Because of this they are not particularly destructive either.
Love Waves, or L-Waves, are what causes damage. These shockwaves run along the surface of the earth and are also commonly called surface waves. L-Waves move and distort the surface in an identical manner to the wave pattern of water. They raise and lower the earth in a rolling wave motion. Although they are much slower than P-Waves and S-Waves they can be lethal in large earthquakes.
L-Waves are the last shockwaves to occur when an earthquake happens.
Minimising Property Damage
When earthquakes occur the chances are the vast majority of people will either be inside, or in the immediate vicinity of buildings. Therefore, it is critical that these buildings can stand up to earthquakes especially in areas that are prone to tremors.
Buildings design and engineering becomes critical as sub-standard materials and practices have and do cost the lives of thousands of people.
Structures that are brittle fare the worst in earthquakes – the surface waves can just tear them apart. Reinforced buildings and high specification concrete can save many lives. However, these measures are only good for moderate earthquakes up to about 6 on the Richter Scale. Above this threshold and more flexible designs have to be incorporated.
These type of buildings require foundations built on moving suspensions and other methods to dissipate the huge forces of energy safely.
In 2008 China experienced a devastating Earthquake that would tear apart the Sichuan Province. 65,000 people were confirmed dead, 374,000 people were injured and a further 18,000 people are still missing and believed to be dead. Furthermore, over four million were left without a home. It is now known that substandard buildings including 7,000 schools contributed greatly to the death toil.
However, what was highly peculiar to engineers were apartments that were left standing. Even though these structures were also sub-standard constructions they did not collapse and disintegrate. The engineers were puzzled so they looked at the design of the building rather than the materials that were used. They found that these apartments had more of a honeycomb structure than the buildings that had collapsed.
In essence, the smaller the rooms and the more pillars and internal walls a building has, the greater its propensity to survive an earthquake.
The Burden Of Life
Earthquakes are not going to go away anytime soon. We just have to continue to live with them as best we can. Our methods of detection and engineering mean that we are in a better position to tolerate them than our ancestors once were.
Though we certainly do not embrace them and they may cause huge loss of life, earthquakes are a sign that our planet is alive, healthy and able to sustain life.
Earthshaking Science: What We Know (And What We Don’t Know) About Earthquakes is a good book by Susan Hough. Like all good books on technical subjects it manages to be both comprehensive and readable.
For people living in Ireland or the United Kingdom you can access Earthshaking Science: What We Know (And What We Don’t Know) About Earthquakes here:
For those living in Canada you can obtain Earthshaking Science: What We Know (And What We Don’t Know) About Earthquakes from here.
For Germany: Earthshaking Science: What We Know (And What We Don’t Know) About Earthquakes.
For France: Earthshaking Science: What We Know (And What We Don’t Know) About Earthquakes.