New insights on plate tectonics

Asthenosphere and lithospheric plate: The Earth’s outer layer is broken into moving, interacting plates whose motion at the surface generates most earthquakes, creates volcanoes and builds mountains. 

In this image, the orange layer represents the deformable, warm asthenosphere in which there is active mantle flow. 

The green layer is the lithospheric plate, which forms at the mid ocean ridge, then cools down and thickness as it moves away from the ridge. 

The cooling of the plate overprints a compositional boundary that forms at the ridge by dehydration melting and is preserved as the plate ages. 

The more easily deformable, hydrated rocks align with mantle flow. 

The directions of past and present-day mantle flow can be detected by seismic waves, and changes in the alignment of the rocks inside and at the bottom of the plate can be used to identify layering.

The Earth's outer layer is made up of a series of moving, interacting plates whose motion at the surface generates earthquakes, creates volcanoes and builds mountains.

Geoscientists have long sought to understand the plates' fundamental properties and the mechanisms that cause them to move and drift, and the questions have become the subjects of lively debate.

A study published online Feb. 27 by the journal Science is a significant step toward answering those questions.

Caroline Beghein

Researchers led by Caroline Beghein, assistant professor of earth, planetary and space sciences in UCLA's College of Letters and Science, used a technique called seismic tomography to study the structure of the Pacific Plate—one of eight to 12 major plates at the surface of the Earth.

The technique enabled them to determine the plate's thickness, and to image the interior of the plate and the underlying mantle (the layer between the Earth's crust and outer core), which they were able to relate to the direction of flow of rocks in the mantle.

"Rocks deform and flow slowly inside the Earth's mantle, which makes the plates move at the surface," said Beghein, the paper's lead author.

"Our research enables us to image the interior of the plate and helps us figure out how it formed and evolved."

The findings might apply to other oceanic plates as well. Even with the new findings, Beghein said, the fundamental properties of plates "are still somewhat enigmatic."

Beghein and her research team advanced our understanding of how oceanic plates form and evolve as they age by using and comparing two sets of seismic data; the study revealed the presence of a compositional boundary inside the plate that appears to be linked to the formation of the plate itself.

More information: "Changes in Seismic Anisotropy Shed Light on the Nature of the Gutenberg Discontinuity." Caroline Beghein, Kaiqing Yuan, Nicholas Schmerr, and Zheng Xing. Science 1246724. Published online 27 February 2014. [DOI: 10.1126/science.1246724]

JAMSTEC: Japan deep sea drilling boat Chikyu casts off to find Earthquakes

Japan's deep-sea drilling vessel Chikyu is anchored at Shimizu port, Shizuoka prefecture on September 11, 2013. 

A Japan-led team of seismologists set off Friday on a mission to drill deep beneath the seabed in a search for the origin of earthquakes.

A Japan-led team of seismologists set off Friday on a mission to drill deep beneath the seabed in a search for the origin of earthquakes.

The scientists weighed anchor on Japan's deep-sea drilling vessel Chikyu, heading for a spot in the ocean off the Kii peninsula, southwestern Japan, and a fracture in the Earth's crust known as the Nankai Trough.

Experts have warned the trough, which marks the place where the Philippine Sea plate slides under the Eurasian plate, is the likely source of a monster earthquake sometime in the near future.

Tamano Omata

Japan's government last year unveiled a worst-case scenario, warning a big quake in the area could kill over 320,000 people, dwarfing the March 11, 2011, quake-tsunami disaster.

In its four-month mission, the latest stage of a multi-year project that began in 2007, the team plans to drill 3,600 metres (2.2 miles) down and take samples from the crust.

They will also be readying for another trip next year in which they hope to get 5,200 metres down, to the spot where the action actually happens.

"It would be unprecedented to drill directly into a seismogenic zone, the area believed to release great energy and cause crusts to slide along fault lines and trigger tsunami," said Tamano Omata, a researcher for the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).

Scientists want to plant sensors—such as seismometers, deformation-measuring devices and thermometers—in the zone, that will form part of a system called Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET), which is linked directly to onshore monitors.

"We expect to become able to monitor how the crusts move immediately before a quake hits," Omata said.

Shinichi Kuramoto

Shinichi Kuramoto, deputy director of JAMSTEC's Center for Deep Earth Exploration, said recent research has shown mild earthquakes, in which the two crusts slip gently past each other, have occurred frequently over stretches of the Nankai Trough in the past five years.

He said it was possible these were precursors to a mega-quake.

"Directly drilling into and observing the place that may release a big quake would be a big step towards understanding the seismological mechanism," he said.

The 56,752-ton Chikyu—"Earth" in Japanese—has been anchored in central Shimizu port, and was open to foreign press this week ahead of the mission.

The vessel, built in 2005 at a cost of $500 million, is equipped with a 121-metre (400-foot) drill tower that can descend 7,000 metres below the seabed, nearly three times as deep as its predecessors.

It depends on satellite location systems with pinpoint accuracy that allow its captain to know exactly where the ship is in relation to the Earth's crust.

Seismically-active Japan experiences 20 percent of the world's major earthquakes every year.

Building standards are high and its people are well-practised at taking cover when quakes strike, meaning damage and death tolls are often much lower than in other parts of the world.

But its proximity to major tectonic faults means the risk is ever-present.

DONET is a submarine cabled real-time seafloor observation infrastructure which was designed to realize precise earthquakes and tsunamis monitoring on seafloor in the long period of time. 

It consists of an approximately 300km length of backbone cable system, 5 science nodes, and 20 observatories. 

Its installation on 20 stations at Kumanonada started in 2006 and has been completed in July 2011.

Volcanic eruption: Stromboli Lava Flow on Sciara del Fuoco

The activity at Stromboli has lately increased, over the holidays. Since 23 December small lava overflows occurred from the eastern crater area and produced lava flows with varying length on the upper part of the Sciara del Fuoco (360deg view).

Yesterday afternoon and evening, it looked as if the lava flow had increased and extended on a good portion of the Sciara where lava blocks detaching from the flow rolling down created a dense incandescent stream.

It is still unclear whether the flows come from a new vent at the eastern crater terrace or whether they are overflows of lava from an existing vent.

The seismic activity has increased and in addition to the tremor, explosion and rockfall, signals are elevated as well.

Such lava (over-)flows from the crater are usually relatively short-lived, but come often in phases.

All news about: Stromboli volcano