Nature is a harsh mistress. The more we study the natural world the more we come to understand how the various natural system are inter-connected. Recently scientists from Florida International University have established a connection between large Typhoons and earthquakes. While earthquakes are a complex event with many causes this is one more piece of the puzzle that will help us understand the world we live in.
The most destructive earthquakes are the result of the Earth’s crust being made of a number of separate plates – tectonic plates – that just won’t stand still. As the plates are made of rock and earth they are rough causing friction as they grind together. This friction causes the plates to lock at the edges while the rest of the plate behind continue to move forward, building up pressure where the plates meet – convergent plate boundaries -. When this pressure is released earthquakes are the result. The amount of energy that is released during an earthquake is astronomical. The total energy released by Japans recent earthquake - total energy or seismic moment – equates to 600 million times the energy released by the Hiroshima atomic bomb. All of that energy had built in the crust and was released in just a few minutes of shaking.
“Very wet rain events are the trigger,” said Wdowinski, associate research professor of marine geology and geophysics at the UM Rosenstiel School of Marine and Atmospheric Science. “The heavy rain induces thousands of landslides and severe erosion, which removes ground material from the Earth’s surface, releasing the stress load and encouraging movement along faults.”
The triggers for this release of energy are varied and still being understood. The theory being investigate by Wdowinski is a beautifully simple premise, large Typhoons – rain events – cause erosion and landslides in hilly and mountainous regions. the reduction of the load - weight – reduces the pressure / energy that has held the built up causing it to be released. Wdowinski and a colleague from Florida International University analyzed data from Taiwan and Haiti, locations that have all of the required ingredients, large mountainous regions, annual Typhoons, a recorded history of earthquakes and the right type of fault, in this case a subduction fault where one tectonic plate is moving over the top of another.
By studying the correlation between large Typhoons followed by earthquake activity they were indeed able to establish a trend. The study looked at four major Typhoons, three in Taiwan – Typhoons Morakot, Herb and Flossie – and one the 2010 Magnitude 7 earthquake in Haiti that followed two massive tropical storms. All three of the Taiwanese Typhoons were followed by earth quakes that ranged from magnitude M 6.2 to M 7.6. 1996 saw Typhoon Herb drench Taiwan and in the years 2 years after saw a M 6.2 and a massive M 7.6 earthquake. Typhoon Morackot 2009 was followed by two major earthquakes, a M 6.2 in 2009 and M 6.4 in 2010.
A number of other triggers for earthquakes are being studied around the world. Geothermal energy extraction is being investigated as one cause, the removal of liquid from the ground shrinks the surrounding area that was holding the water and frees up the fault. The process of Fracing – injecting liquid to extract coal gas – to extract coal gas is thought to lubricate the fault lines allowing them to more easily slide. These are all possible triggers that are being investigated.
Earthquakes are one of Natures greatest demonstrations of power and one of the most destructive forces that we as citizens of Earth must deal with. While there is zero chance of man-kind being able to halt this destructive force understanding of the triggers is essential to improving our ability to predict and prepare for seismic events.