Normal Faults

Definition

Normal faults are a type of geological fault where the hanging wall moves downward relative to the footwall, caused by extensional forces that pull the Earth's crust apart. These faults are key players in mountain building and continental formation, as they help create rift valleys and can lead to the uplift of mountain ranges during tectonic activity.

5 Must Know Facts For Your Next Test

1. Normal faults commonly occur at divergent plate boundaries, where tectonic plates are moving away from each other.
2. They can create significant topographical features, such as basins and mountain ranges, due to the vertical displacement of rock.
3. The hanging wall block in a normal fault is always located above the fault plane, while the footwall block is below it.
4. Normal faults can also trigger earthquakes, which can occur when accumulated stress along the fault line exceeds the strength of the rocks.
5. Famous examples of normal faults include the East African Rift and the Basin and Range Province in the western United States.

Review Questions

• How do normal faults contribute to geological features like rift valleys and mountain ranges?
  • Normal faults play a significant role in forming geological features such as rift valleys and mountain ranges. As tectonic plates pull apart due to tension, normal faults occur, allowing the hanging wall to slip down relative to the footwall. This process creates rift valleys where land has sunk between fault lines and leads to uplifted regions that form mountain ranges as sections of the crust are raised. The interaction between these processes shapes the landscape over geological time.
• Discuss the relationship between normal faults and tectonic plate movements at divergent boundaries.
  • Normal faults are closely linked to tectonic plate movements at divergent boundaries, where plates move away from each other. This movement creates tension in the Earth's crust, resulting in the formation of normal faults. As these faults develop, they facilitate further extension and thinning of the crust, contributing to rift valley formation. The ongoing activity at these boundaries leads to continuous geological changes and can result in significant seismic events.
• Evaluate the impact of normal faulting on local ecosystems and human infrastructure in areas prone to these geological features.
  • Normal faulting can have profound effects on local ecosystems and human infrastructure in areas prone to such geological features. The creation of rift valleys can alter drainage patterns, leading to changes in water availability and habitats for flora and fauna. Additionally, increased seismic activity associated with normal faults poses risks to infrastructure like buildings and roads, making it essential for urban planning in these regions to consider geological hazards. Understanding these impacts allows for better preparedness and mitigation strategies in affected communities.

Related terms

Tension:

A stress force that stretches rock and is a primary driver of normal faulting as it pulls the crust apart.

Rift Valley: A lowland region that forms where tectonic plates move apart, often characterized by normal faults.

Fault Scarp: A steep slope or cliff formed when one side of a fault moves relative to the other, often visible in normal faulting.