The mystery of too-deep earthquakes

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

KD4_fig_1
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

An adventure on the JOIDES Resolution: One year later

cf_dec2016_fig1
Fig. 1 – (Top) One of the many magnificent sunrises observed by scientists on board the JR; (Bottom) View of the derrick, tower that holds the drill string, from the Bridge Deck, and (Top-left) all Expedition 360 participants. Images credits: William Crawford, Exp. 360 Senior Imaging Specialist; Jiansong Zhang, Exp. 360 Education/Outreach Officer.

Earlier this year Barbara wrote about ‘Life on board of a scientific drilling vessel’. That interview gave some hints in the unique experience my colleagues and I shared on board the Joides Resolution. Now, you might wonder what Joides Resolution (JR) exactly is. The JR is a drilling vessel dedicated to scientific research on ocean and ocean crust dynamics. Different disciplines are involved, from geology (to elucidate the formation of the oceanic crust), to climate change science (to understand how the Earth handled past climatic events), oceanography (to study global water circulation), or microbiology (to track extreme life in rocks forming the ocean floor).Cores of rocks are drilled under the ocean floor, giving scientists a glimpse into Earth’s dynamics. The JR works for the international research program IODP (International Ocean Discovery Program), a marine research collaboration that aims at recovering data recorded in seafloor sediments and rocks, and monitoring subseafloor environments. Continue reading

Breaking rocks: a closer look

When I described in my last post how rocks can be broken up by volume-increasing reactions happening within them, I left you with several open questions in the end. One of them was whether reaction-driven fracturing can also occur when there is no stress from the outside and no fracture to start with. It is easy enough to imagine that minerals that grow in a crack may push against the walls of the crack, move them apart and cause further fracturing. But for this first crack, with which everything starts, we certainly need some forces from the outside that make the rock break. Or do we really?

Continue reading

Continued: The story of the deep carbon cycle…

… and the big black bear

Last summer, I was fighting my way through the boreal forests of Newfoundland in Canada, a place well renowned for its wildlife. Hence I was heavily armoured with big hammers, a huge can of strong pepper spray and some bear banger cartridges in my pocket, always smelling of mosquito repellent and making a lot of noise, in order not to surprise a sleeping black bear in the bushes. In the end, I didn’t need the bear spray or the cartridges, but every now and then signs of bears in our field area reminded us of their presence. And I took these safety measures much more seriously after we encountered a black bear close to a local landfill: you just feel small and vulnerable in front of such a huge, beautiful and elegant animal that is only 20 meters away from you, even if your car is just two meters behind you.

MM2-1
Fig1. Some of the wild life a geologist might need to be worried about.

Continue reading

Ocean crust: What is beneath the seafloor?

Have you ever thought about what happens beneath the oceans? What rocks below the seafloor might look like? And how we know about them?

Well, almost 70% of the Earth`s surface is covered by oceans. This means that ocean crust makes up the biggest part of the whole Earth’s surface, notably more than the continental crust that we live on! Continue reading

Fête de la Science wrap up

Abyss ITN hosted a Fête de la Science event at IPGP on the ocean crust on October 9, 2015. All of us here at SeaRocks want to thank those who attended our event! We hope you all enjoyed it! The event kicked off with the arrival of students from three schools: Lycée Henri Bergson (Paris 19e), Lycée Flora Tristan (Noisy-le-Grand), and Lycée Suger (Saint-Denis). The students then rotated through three different workshops related to the scientific topics investigated within the ABYSS network. Continue reading