Asthenosphere

Definition

The asthenosphere is a semi-fluid layer of the Earth's mantle, located beneath the lithosphere, which plays a crucial role in tectonic plate movement. It is characterized by its ability to flow and deform under pressure, enabling the lithospheric plates to glide over it. This property connects it to the generation of seismic waves, the reflection and refraction of body waves, and the overall dynamics of the Earth's internal structure.

5 Must Know Facts For Your Next Test

1. The asthenosphere extends from about 100 kilometers to 410 kilometers below the Earth's surface, making it an integral part of the upper mantle.
2. Its semi-fluid nature allows for convection currents, which are essential for driving plate tectonics and influencing geological processes.
3. The viscosity of the asthenosphere is significantly lower than that of the overlying lithosphere, which allows seismic S-waves to be blocked while P-waves can still pass through.
4. Seismic studies have shown that variations in the properties of the asthenosphere can lead to changes in the velocity of seismic waves, providing insights into its structure.
5. The asthenosphere is involved in subduction zone dynamics, where tectonic plates converge, leading to intense seismic activity and geological formations.

Review Questions

• How does the asthenosphere contribute to the movement of tectonic plates?
  • The asthenosphere's semi-fluid properties allow tectonic plates in the lithosphere to move and glide over it. This layer acts like a lubricating layer beneath the rigid plates, enabling them to shift due to convection currents in the mantle. The flow within the asthenosphere facilitates various tectonic activities such as earthquakes and volcanic eruptions as these plates interact.
• In what ways do S-waves behave differently when passing through the asthenosphere compared to the lithosphere?
  • S-waves, or secondary waves, cannot travel through fluids, which means their propagation is affected by the physical state of materials they encounter. While they can travel through the solid lithosphere, they are blocked when they reach the asthenosphere due to its semi-fluid characteristics. This contrast in behavior provides essential information about Earth's internal structure and helps seismologists map different layers within the Earth.
• Evaluate how variations in asthenospheric properties can influence seismic activity and plate tectonic processes.
  • Variations in temperature, composition, and viscosity within the asthenosphere can greatly affect how tectonic plates move and interact. For example, a hotter or more ductile asthenosphere may lead to increased movement of tectonic plates, resulting in more frequent seismic events. Conversely, cooler regions may create resistance against plate movements. Understanding these variations allows scientists to better predict seismic activity and comprehend geological phenomena like subduction zones and rift valleys.

Related terms

Lithosphere:

The rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle, which is broken into tectonic plates.

Seismic Waves: Energy waves generated by earthquakes or other geological events that travel through the Earth, including both body waves and surface waves.

Plate Tectonics: The scientific theory that describes the large-scale movements of Earth's lithosphere, explaining phenomena such as earthquakes, volcanic activity, and continental drift.