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

Rocks that pop!

  • Discovery

In 1972, the scientists onboard the French research vessel Jean Charcot, during the “Midland” cruise made an amazing discovery: Rocks that pop! From the seafloor in the Atlantic Ocean they retrieved some basaltic glassy pebbles that exploded noisily, much like firecrackers and jumped merrily to a height of up to one meter on the ship deck. A decade later, another geologic expedition aboard the RV Akademik Boris Petrov made the same surprising discovery from a complex region of the Mid-Atlantic Ridge that contains vast areas of lava flows (see previous post) as well as heavily faulted terrain with intact blocks of deep crust. These rare forms of lava rock are really interesting because of their spectacular behaviour but mostly because of their richness in gas and information they provide on the deep Earth.

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Figure 1: a) Photo of a popping rock. Volcanic glass in black and rounded vesicles. b) Photo of a thin section of popping rock (Sarda, 1990).

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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

Behind the scenes: starting a petrological experiment!

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1. A: Gold capsules (not bullets) containing rock and fluid, 2 cm in length. B: Balance used to weigh capsules and their content

I had never thought experimental petrology could resemble cooking to such an extent. With some imagination you can replace the basic ingredients of your favourite pie recipe and use a rather special type of oven to make the magic happen. Actually, every experiment has its own experimental “cooking” setup, with the desired quantities of components raised to specific pressures and temperatures that will (hopefully) lead your experiment to success. Continue reading

How to reproduce inner Earth pressure and temperature in a laboratory

Earth’s inner structure
Earth’s inner structure.

Drilling allows us to collect samples from the inner Earth, which provide us an idea of its composition and internal hidden processes.The deepest scientific drilling on Earth reached 12.262 km into the crust (Kola Superdeep Borehole in Russia), but what does it represent? The Earth has a radius of 6,378 km which is significantly greater than the 12 km of crust drilled at depth in Russia (Image 1). However it is extremely costly, time consuming, and for the moment there is no existing technology that would allow us to drill deep in the upper mantle (from 5 to 100 km deep). Therefore in order to complete our knowledge of Earth’s interior, geologists have to use different strategies, for example geophysical imaging. Another, less known possibility is experimental petrology, or “how to cook your own rocks”. Continue reading