The mystery of too-deep earthquakes

Look at the depth distribution of earthquakes on Earth (Fig. 1):

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Fig. 1: Depths of earthquakes on Earth. Shallow earthquakes (0-60 km) are in red, intermediate-depth earthquakes (60-300 km) in purple and deep earthquakes (>300 km) in blue. Data from the International Seismological Centre.

In general, earthquakes are located at the boundaries between tectonic plates. Shallow earthquakes (< 60 km) happen at all plate boundary types, but intermediate (60-300 km) and deep (> 300 km) earthquakes mainly occur in subduction zones, where one plate moves beneath another. Because these earthquakes are located either within the subducting plate or between the two plates, they get deeper and deeper the further they are from the surface trace of the plate boundary. Because the plate located west of South-America moves towards the east and is subducted under South-America (Fig. 2), the earthquakes on the west coast of South-America get deeper from west to east (Figs 1, 2). Continue reading

A Journey to the center of the Earth

You may think that travelling to the center of the Earth is just science fiction. Impossible even? Yet, perhaps it is possible…

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Fig. 1: Jules Vernes novel, ‘A Journey to the Centre of the Earth’, source : Penguin.co.uk

Jules Verne’s famous novel from 1864, ‘Journey to the Center of the Earth’, has inspired many people to wonder what the center of our planet is like and, if we could ever go there, what might we find? Since then we have learned much about the inner workings of our planet but it hasn’t stopped science fiction writers or scientists from imagining some way of getting there. But first, let’s go over what we do know about the interior of the planet. The Earth has a radius of 6378.1 kilometers. The innermost 1,210 km kilometers is the solid inner core that is thought to be mostly composed of iron and has a temperature of around 5400°C. This is surrounded by the outer liquid core (2,260 km thick) with the same composition. The convecting liquid of the outer core drives the Earth’s magnetic field, which protects us from the solar wind. Beyond this is the mantle that stretches from around 35 km to 2,890 km. The outermost layer is the crust, which is approximately 35 km thick under the continents and 6 km in the oceans. So, how far can we get into the Earth to find out more? Continue reading