Tag Archives: crust

Eight Seconds of Terror

A JPL Scientist Reflects on L.A.’s Last Big Quake

Twenty years ago this week, in the predawn darkness of Jan. 17, 1994, at five seconds before 4:31 a.m. PST, the ground ruptured violently on a blind thrust fault (a crack in Earth’s crust that does not reach the surface) about 11 miles (18 kilometers) beneath Reseda, in California’s San Fernando Valley about 20 miles (31 kilometers) northwest of downtown Los Angeles. The resulting magnitude 6.7 earthquake, known as the Northridge earthquake, became the first large quake to strike directly under an urban area in the United States since the 1933 magnitude 6.4 earthquake in Long Beach, Calif. (more…)

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Some volcanoes ‘scream’ at ever-higher pitches until they blow their tops

It is not unusual for swarms of small earthquakes to precede a volcanic eruption. They can reach a point of such rapid succession that they create a signal called harmonic tremor that resembles sound made by various types of musical instruments, though at frequencies much lower than humans can hear.

A new analysis of an eruption sequence at Alaska’s Redoubt Volcano in March 2009 shows that the harmonic tremor glided to substantially higher frequencies and then stopped abruptly just before six of the eruptions, five of them coming in succession. (more…)

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Lunar impacts created seas of molten rock

A new analysis of data from NASA’s Lunar Orbiter Laser Altimeter (LOLA) shows that molten rock may have been present on the Moon more recently and for longer periods than previously thought. Differentiation — a settling out of rock layers as liquid rock cools — would require thousands of years and a fluid rock sea at least six miles deep.

PROVIDENCE, R.I. [Brown University] — Early in the Moon’s history an ocean of molten rock covered its entire surface. As that lunar magma ocean cooled over millions of years, it differentiated to form the Moon’s crust and mantle. But according to a new analysis by planetary scientists from Brown University, this wasn’t the last time the Moon’s surface was melted on a massive scale. (more…)

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Magma in Earth’s Mantle Forms Deeper Than Once Thought

Study simulating pressures in mantle beneath the ocean floor shows that rocks can melt at depths up to 250 kilometers

Magma forms far deeper than geologists previously thought, according to new research results.

A team led by geologist Rajdeep Dasgupta of Rice University put very small samples of peridotite, rock derived from Earth’s mantle, under high pressures in a laboratory.

The scientists found that the rock can and does liquify, at least in small amounts, at pressures equivalent to those found as deep as 250 kilometers down in the mantle beneath the ocean floor. (more…)

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Clean Energy From CO2?

Global warming villain CO2 may have a surprisingly green future

The next frontier in the search for renewable energy lies less than two miles from where you are now.

Unless you’re reading this on the International Space Station.

Geothermal heat a mile or two deep in Earth’s crust is a potential source of energy that could be tapped by an unlikely carrier: carbon dioxide (CO2), the central villain in global warming. That energy, unlike solar and wind, could be easily turned on and off without the intermediate step of being stored in a battery. And it would be constant and reliable. (more…)

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New Understanding of Earth’s Mantle Beneath The Pacific Ocean

Washington, D.C. — Scientists have long speculated about why there is a large change in the strength of rocks that lie at the boundary between two layers immediately under Earth’s crust: the lithosphere and underlying asthenosphere. Understanding this boundary is central to our knowledge of plate tectonics and thus the formation and evolution of our planet as we know it today. A new technique for observing this transition, particularly in the portion of Earth’s mantle that lies beneath the Pacific Ocean basin, has led Carnegie and NASA Goddard scientist Nick Schmerr to new insight on the origins of the lithosphere and asthenosphere. His work is published March 23 in Science.

The lithosphere-asthenosphere boundary, or LAB, represents the transition from hot, convecting mantle asthenosphere to overlying cold and rigid lithosphere. The oceanic lithosphere thickens as it cools over time, and eventually sinks back into the mantle at Earth’s so-called subduction zones. (more…)

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Building Blocks of Early Earth Survived Collision that Created Moon

COLLEGE PARK, Md. – Unexpected new findings by a University of Maryland team of geochemists show that some portions of the Earth’s mantle (the rocky layer between Earth’s metallic core and crust) formed when the planet was much smaller than it is now, and that some of this early-formed mantle survived Earth’s turbulent formation, including a collision with another planet-sized body that many scientists believe led to the creation of the Moon.

“It is believed that Earth grew to its current size by collisions of bodies of increasing size, over what may have been as much as tens of millions of years, yet our results suggest that some portions of the Earth formed within 10 to 20 million years of the creation of the Solar System and that parts of the planet created during this early stage of construction remained distinct within the mantle until at least 2.8 billion years ago.” says UMD Professor of Geology Richard Walker, who led the research team. (more…)

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3-D Laser Map Shows Earthquake Zone Before and After

*Geologists learn how earthquakes change the landscape — down to a few inches*

Geologists have a new tool to study how earthquakes change the landscape–down to a few inches. It’s giving scientists insights into how earthquake faults behave.

In this week’s issue of the journal Science, a team of scientists from the United States, Mexico and China reports the most comprehensive before-and-after picture yet of an earthquake zone, using data from the magnitude 7.2 event that struck near Mexicali, Mexico, in April 2010. (more…)

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