Megathrust Earthquakes- The Big Ones

Is an earthquake of magnitude 10.5 possible? They call it as a megaquake and scientists say it is theoretically while practically not possible. Let us discuss some basic understanding of earthquakes, the megathrust earthquakes and the possibility of a 10.5 ‘Big One’. 

Earthquake is a natural phenomenon the earth surface or the tectonic plates have devised to release some form of energy when a greater pressure is built beyond the threshold.

This release of the stored elastic strain energy can happen along the boundary lines, called as faults of two tectonic plates or away from the faults towards the broader areas of the plates. Normally tectonic plates run 100 km thick below the earth’s surface.

Earthquakes happening due to the adjustment of two tectonic plates at their meeting point can be deadly because of the frictional force exerted by the two different Plates. The 7.8 magnitude earthquake near Lamjung, Nepal occurred at the plate boundary of the India Plate and the Eurasian Plate, says the U.S. Geological Survey.

The Eurasian Plate is one of the primary plates among the seven with the other six being African, Antarctic, Indo-Australian, North American, Pacific and South American Plates. The primary plates cover most of the earth’s lithosphere. 

The Indian Plate falls under the secondary plates category with a few other being Arabian, Carribean, and Philippine Sea plates. There are also tertiary plates that cover a very small region, but even then they may drift apart frequently.

As a well known fact, an earthquake is measured in Richter magnitude scale, which is in geology considered to be earthquakes of lower magnitude.

There is another scale known as moment magnitude scale that represents very powerful earthquakes of magnitude 9 or above. This is where the concept of megaquakes or megathrust earthquakes comes in. They are also known as ‘The Big Ones’

These types of earthquakes are very much catastrophic as they happen between subducted tectonic plates or in other words, a plate being pushed beneath another. This form of movement that is one fault of the plate being underneath another one is called as thrust. 

The Sumatra earthquake in 2004 was a megathrust earthquake because of the subduction between the Indian and the Burman Plates and is the third worst earthquake recorded in history with the second being The Great Alaska earthquake in 1964. 

The worst hit earthquake in history was the Valdivia earthquake in 1960 with a recorded moment magnitude of 9.5 killing 1655 in 10 minutes and displacing two million. This was due to the subduction between Nazca Plate and South American Plate and the fault runs 1000 km long.

The possibility of a real Big One

Geologists say an earthquake of magnitude 10 or above is implausible, even though there is no cap assured by nature in the magnitude scale of earthquakes. The reasoning behind the conclusion is the length of faults.

Geological science says the more the length of the tectonic plate boundaries, the more devastating are the effects of earthquakes as a result of their subduction.  There exists no such fault running greater lengths to create such a massive catastrophe under our comprehensive study of earthquakes.

In fact, we have started measuring earthquakes only very recently over the past 100 years.  What causes such seismic activities that release energy resulting in the destruction of thousands of lives? Well, the earth surface feels the pressure and starts vibrating.

We have got some interesting numbers. These vibrations travel up to a speed of 14 km per second and at the fastest rate these vibrations can reach the other side of the earth surface that is 13000 km away in a matter of less than 20 minutes.  Such amazing stuffs can nature do.

The reason why the earth surface vibrates or the elastic strain energy is released is, may be just because it exists.

Image Source: The Telegraph

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