Asthenosphere

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Asthenosphere

The asthenosphere (from an invented Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
a + 'sthenos "narrow or constricted" and Greek word sfa??a (sphera) meaning globe) is the mechanically weak ductily-deforming region of the upper mantle
Mantle (geology)

The mantle is a part of an astronomical object. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers....
of the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
. It lies below the lithosphere
Lithosphere

File:Plates tect2 en.svgFile:Earth-crust-cutaway-english.svgThe lithosphere is the rigid outermost shell of a rocky planet....
, at depths between 100 and 200 km (~ 62 and 124 miles) below the surface, but perhaps extending as deep as 400 km (~ 249 miles).

asthenosphere is a portion of the upper mantle just below the lithosphere
Lithosphere

File:Plates tect2 en.svgFile:Earth-crust-cutaway-english.svgThe lithosphere is the rigid outermost shell of a rocky planet....
that is involved in plate movements
Plate tectonics

Plate tectonics describes the large scale motions of Earth's lithosphere. The theory encompasses the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, understood during the 1960s....
and isostatic
Isostasy

Isostasy is a term used in geology to refer to the state of gravity equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density....
adjustments.

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The asthenosphere (from an invented Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
a + 'sthenos "narrow or constricted" and Greek word sfa??a (sphera) meaning globe) is the mechanically weak ductily-deforming region of the upper mantle
Mantle (geology)

The mantle is a part of an astronomical object. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers....
of the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
. It lies below the lithosphere
Lithosphere

File:Plates tect2 en.svgFile:Earth-crust-cutaway-english.svgThe lithosphere is the rigid outermost shell of a rocky planet....
, at depths between 100 and 200 km (~ 62 and 124 miles) below the surface, but perhaps extending as deep as 400 km (~ 249 miles).

Characteristics
The asthenosphere is a portion of the upper mantle just below the lithosphere
Lithosphere

File:Plates tect2 en.svgFile:Earth-crust-cutaway-english.svgThe lithosphere is the rigid outermost shell of a rocky planet....
that is involved in plate movements
Plate tectonics

Plate tectonics describes the large scale motions of Earth's lithosphere. The theory encompasses the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, understood during the 1960s....
and isostatic
Isostasy

Isostasy is a term used in geology to refer to the state of gravity equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density....
adjustments. In spite of its heat, pressures keep it plastic
Plasticity (physics)

In physics and materials science, plasticity describes the deformation of a material undergoing non-reversible changes of shape in response to applied forces....
, and it has a relatively low density. Seismic
Seismology

Seismology is the scientific study of earthquakes and the propagation of Linear elasticity#Elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes ....
waves pass relatively slowly through the asthenosphere, compared to the overlying lithospheric mantle, thus it has been called the low-velocity zone. This was the observation that originally alerted seismologists
Seismology

Seismology is the scientific study of earthquakes and the propagation of Linear elasticity#Elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes ....
to its presence and gave some information about its physical properties, as the speed of seismic waves decreases with decreasing rigidity
Rigidity

Generally, rigidity refers to inflexibility or resistance to change. It has a number of specific meanings depending on the field of application....
.

Under the thin ocean
Ocean

An ocean is a major body of Seawater, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a World Ocean that is customarily divided into several principal oceans and smaller seas....
ic plates the asthenosphere is usually much nearer the seafloor surface, and at mid-ocean ridge
Mid-ocean ridge

A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics....
s it rises to within a few kilometers of the ocean floor.

The upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric plates of the Earth's crust
Tectonic Plate

#REDIRECT Plate tectonics...
move about. Due to the temperature
Temperature

In physics, temperature is a physical property of a Physical system that underlies the common notions of hot and cold; something that feels hotter generally has the greater temperature....
and pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
conditions in the asthenosphere, rock
Rock (geology)

In geology, rock is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock....
becomes ductile, moving at rates of deformation measured in cm/yr over lineal distances eventually measuring thousands of kilometers. In this way, it flows like a convection
Convection

Convection in the most general terms refers to the movement of molecules within fluids . Convection is one of the major modes of heat transfer and mass transfer....
current, radiating heat outward from the Earth's interior. Above the asthenosphere, at the same rate of deformation, rock behaves elastically and, being brittle, can break, causing faults
Geologic fault

In geology, a fault or fault line is a planar Fracture in rock in which the rock on one side of the fracture has moved with respect to the rock on the other side....
. The rigid lithosphere is thought to "float" or move about on the slowly flowing asthenosphere, creating the movement of crustal plates described by Plate tectonics
Plate tectonics

Plate tectonics describes the large scale motions of Earth's lithosphere. The theory encompasses the older concepts of continental drift, developed during the first decades of the 20th century by Alfred Wegener, and seafloor spreading, understood during the 1960s....
theory.

Historical
Although its presence was suspected as early as 1926, the worldwide occurrence of the asthenosphere was confirmed by analyses of earthquake
Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph....
waves from the Great Chilean Earthquake
Great Chilean Earthquake

The 1960 Valdivia earthquake or Great Chilean Earthquake of 22 May, 1960 is to date the most powerful earthquake ever recorded, rating 9.5 on the moment magnitude scale....
of May 22, 1960.

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