Moho

Definition

The Moho, or Mohorovičić discontinuity, is the boundary that separates the Earth's crust from the underlying mantle. It is characterized by a distinct change in seismic wave velocities, indicating a transition from the relatively rigid and less dense crust to the denser and more fluid mantle below. Understanding the Moho is crucial as it helps geologists comprehend the structure and composition of the Earth’s internal layers.

5 Must Know Facts For Your Next Test

1. The Moho was first identified in 1909 by seismologist Andrija Mohorovičić, after whom it is named.
2. Seismic waves travel faster in the mantle than in the crust, with a significant increase in velocity occurring at the Moho boundary.
3. The depth of the Moho varies globally, typically found at about 5 to 10 kilometers beneath oceanic crust and 20 to 70 kilometers beneath continental crust.
4. The composition of the crust above the Moho differs significantly from that of the mantle below, with the crust being primarily composed of lighter silicate rocks like granite and basalt.
5. Understanding the Moho's characteristics aids in studying tectonic activity, earthquakes, and volcanic processes since it marks a critical transition between two different layers of Earth.

Review Questions

• How does the Moho influence seismic wave behavior as they travel through different layers of the Earth?
  • The Moho serves as a crucial boundary where there is a notable change in material properties between the crust and mantle. When seismic waves reach this discontinuity, they experience a significant increase in velocity due to the transition from less dense materials in the crust to denser materials in the mantle. This change affects how waves propagate through the Earth and helps geologists understand subsurface structures.
• Discuss how understanding the Moho can help scientists learn about plate tectonics and geological processes.
  • Studying the Moho provides insights into plate tectonics because it marks an essential boundary between tectonic plates that float on top of the mantle. Knowledge of its depth and characteristics informs scientists about tectonic activity such as subduction zones, rifting, and mountain building. By examining seismic data related to the Moho, researchers can better predict volcanic eruptions and earthquakes by understanding stress accumulation and release within these geological structures.
• Evaluate the significance of variations in Moho depth across different geological settings and how this impacts our understanding of Earth's internal processes.
  • Variations in Moho depth provide valuable information about geological history and processes at play beneath various regions. For instance, areas with a shallower Moho often indicate regions that have undergone significant tectonic uplift or are associated with mid-ocean ridges. Conversely, deeper Moho depths can suggest areas with thicker continental crust or regions that have experienced subsidence. Understanding these variations enhances our knowledge of Earth's thermal structure, mineral resources, and dynamics related to plate interactions.

Related terms

Lithosphere: The rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle, characterized by its strength and ability to hold tectonic plates.

Asthenosphere: The layer of the upper mantle located just below the lithosphere, where rock is partially molten and allows for the movement of tectonic plates.

Seismic Waves: Waves of energy that travel through the Earth's layers, produced by geological events like earthquakes, which help scientists study the structure of the Earth's interior.