The devastating tsunami that struck Japan’s Tohoku region in March 2011 was touched off by a submarine earthquake far more massive than anything geologists had expected in that zone.
An international team of scientists has concluded that an unusually thin and slippery geological fault where the North American plate rides over the edge of the Pacific plate caused a massive displacement of the seafloor off the coast of Japan in March 2011, touching off the devastating tsunami that struck the Tohoku region.
Now, a team of scientists including McGill University geologist Christie Rowe, has published a set of studies in the journal Science that shed light on what caused the dramatic displacement of the seafloor off the northeastern coast of Japan. The findings also suggest that other zones in the northwest Pacific may be at risk of similar huge earthquakes.
Prof. Rowe, of McGill’s Department of Earth & Planetary Sciences, was one of 27 scientists from 10 countries who participated in a 50-day expedition in 2012 on the Japanese drilling vessel Chikyu. The team drilled three holes in the Japan Trench area to study the rupture zone of the 2011 earthquake, a fault in the ocean floor where two of the Earth’s major tectonic plates meet, deep beneath the surface of the Pacific Ocean.
The joint where the Pacific and North American plates meet forms what is known as a “subduction” zone, with the North American plate riding over the edge of the Pacific plate. The latter plate bends and plunges deep into the earth, forming the Japan Trench.
The conventional view among geologists has been that deep beneath the seafloor, where rocks are strong, movements of the plates can generate a lot of elastic rebound. Closer to the surface of the seafloor, where rocks are softer and less compressed, this rebound effect was thought to taper off.
Until 2011, the largest displacement of plates ever recorded along a fault occurred in 1960 off the coast of Chile, where a powerful earthquake displaced the seafloor plates by an average of 20 metres. In the Tohoku earthquake, the slip amounted to 30 to 50 metres – and the slip actually grew bigger as the subterranean rupture approached the seafloor. This runaway rupture thrust up the seafloor, touching off the horrifying tsunami.
The results of last year’s drilling by the Chikyu expedition, outlined in the Science papers published Dec. 6, reveal several factors that help account for this unexpectedly violent slip between the two tectonic plates.
For one thing, the fault, itself, is very thin – less than five metres thick in the area sampled. “To our knowledge, it’s the thinnest plate boundary on Earth,” Rowe says. By contrast, California’s San Andreas fault is several kilometers thick in places.
The scientists also discovered that the clay deposits that fill the narrow fault are made of extremely fine sediment. “It’s the slipperiest clay you can imagine,” says Rowe. “If you rub it between your fingers, it feels like a lubricant.”
The discovery of this unusual clay in the Tohoku slip zone suggests that other subduction zones in the northwest Pacific where this type of clay is present – from Russia’s Kamchatka peninsula to the Aleutian Islands – may be capable of generating similar, huge earthquakes, Rowe adds.
To conduct the studies, the scientists used specially designed deep-water drilling equipment that enabled them to drill more than 800 metres beneath the sea floor, in an area where the water is around 6,900 metres deep. No hole had ever before been drilled that deep in an area of similar water depth. At those extraordinary depths, it took six hours from the time the drill pulled core samples from the fault until it reached the ship.
During night shifts on deck, Rowe was in charge of deciding which sections of drill core would go to geochemists for water sampling, and which would go to geologists for studies of the sediment and deformation structures. “We X-rayed the core as soon as it came on board, so the geochemists could get their water sample before oxygen was able to penetrate inside the pores of the sediment.”
The expedition was supported by member countries of the Integrated Ocean Drilling Program (particularly Japan and the US), and Canadian participants were supported by the European Consortium for Ocean Research Drilling, of which Canada is a member.
Link to the expedition website: http://www.jamstec.go.jp/chikyu/exp343/e/
Chris Chipello | Newswise
In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ
Controlling electronic current is essential to modern electronics, as data and signals are transferred by streams of electrons which are controlled at high speed. Demands on transmission speeds are also increasing as technology develops. Scientists from the Chair of Laser Physics and the Chair of Applied Physics at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) have succeeded in switching on a current with a desired direction in graphene using a single laser pulse within a femtosecond ¬¬ – a femtosecond corresponds to the millionth part of a billionth of a second. This is more than a thousand times faster compared to the most efficient transistors today.
Graphene is up to the job
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
26.09.2017 | Life Sciences
26.09.2017 | Physics and Astronomy
26.09.2017 | Information Technology