Question

Which of the following places represent a Wadati-Benioff zone? a. \(10^{\circ} \mathrm{S}, 110^{\circ} \mathrm{W}\) b. \(0^{\circ}, 0^{\circ}\) c. \(15^{\circ} \mathrm{S}, 180^{\circ}\) d. \(30^{\circ} \mathrm{N}, 75^{\circ} \mathrm{E}\)

Short answer

Option c. \(15^{\circ} \mathrm{S}, 180^{\circ}\) represents a Wadati-Benioff zone.

Step-by-step solution

Understand the Wadati-Benioff Zone

A Wadati-Benioff zone is a seismically active area that occurs in subduction zones where one tectonic plate is forced under another. These zones are typically characterized by a series of earthquakes that can be tracked at increasing depths.

Locate the Coordinates

Identify the coordinates for each option:- a. \(10^{\circ} \mathrm{S}, 110^{\circ} \mathrm{W}\)- b. \(0^{\circ}, 0^{\circ}\)- c. \(15^{\circ} \mathrm{S}, 180^{\circ}\)- d. \(30^{\circ} \mathrm{N}, 75^{\circ} \mathrm{E}\)

Identify Subduction Zones

Determine if each coordinate lies near a known subduction zone. Subduction zones are primarily located around the Pacific Ocean (Pacific Ring of Fire), in regions such as the western Pacific, eastern Indian Ocean, and some parts of the Atlantic Ocean.

Match Coordinates to Known Subduction Zones

- a. \(10^{\circ} \mathrm{S}, 110^{\circ} \mathrm{W}\) - This location is in open ocean, not near a subduction zone.- b. \(0^{\circ}, 0^{\circ}\) - This is the intersection of the Equator and the Prime Meridian, no tectonic activity.- c. \(15^{\circ} \mathrm{S}, 180^{\circ}\) - This location is near the Tonga-Kermadec Trench, a very active subduction zone.- d. \(30^{\circ} \mathrm{N}, 75^{\circ} \mathrm{E}\) - This location is in northern India, not near a direct subduction zone.

Conclusion

Only option c. \(15^{\circ} \mathrm{S}, 180^{\circ}\) is close to the Tonga-Kermadec Trench, which is a Wadati-Benioff zone. Other locations do not correlate with any known subduction zones.

Key concepts

Subduction Zones

Subduction zones are areas on the Earth's surface where one tectonic plate slides beneath another. This process usually happens at convergent boundaries where two plates move towards each other. The denser plate (usually oceanic crust) gets forced underneath the less dense plate (usually continental crust or newer oceanic crust). This action leads to a deep oceanic trench, which marks the surface expression of the plate boundary.
Subduction zones are vital because they are locations of intense geological activity including:

• Earthquakes: The grinding and friction between plates often lead to seismic events.
• Volcanoes: Melting of the subducted plate forms magma, which can rise to create volcanic activity.
• Mountain Building: The pressure and heat cause sediments and crustal material to fold and create mountain ranges.

Understanding subduction zones is crucial for comprehending many of Earth's major geological features and processes. The destruction and creation of crust material in these processes are essential parts of the plate tectonics cycle.

Tectonic Plates

Tectonic plates are massive slabs of Earth's lithosphere, which is the outer shell of the planet. These plates float on top of the semi-fluid asthenosphere, allowing them to move.
There are several major and minor tectonic plates covering Earth, such as the Pacific Plate, North American Plate, Eurasian Plate, and others. The boundaries where these plates meet are the locations of significant geological phenomena.
There are three main types of plate boundaries:

• Convergent Boundaries: Where plates push towards each other, often forming subduction zones.
• Divergent Boundaries: Where plates move away from each other, allowing magma to rise and create new crust, seen at mid-ocean ridges.
• Transform Boundaries: Where plates slide horizontally past each other, often causing earthquakes, such as the San Andreas Fault in California.

The movement of tectonic plates is driven by forces such as mantle convection, slab pull, and ridge push. Understanding how tectonic plates function helps us grasp the dynamic nature of our planet and the events like earthquakes, volcanic eruptions, and ocean formation.

Seismic Activity

Seismic activity refers to the frequency and intensity of earthquakes experienced over a period in a certain area. It is predominantly influenced by the tectonic movements and is often concentrated in regions where tectonic plates interact, such as subduction zones.
In a Wadati-Benioff zone, seismic activity is high due to the subduction process. Here, earthquakes occur at varying depths as the subducting plate descends into the mantle. Such depth-varying earthquakes are a hallmark of these zones.
Seismic activity is detected and measured using instruments called seismometers, which record the vibrations caused by ground movement. Researchers assess this data to understand:

• The location and depth of earthquakes.
• The stress and strain in Earth's crust.
• The potential risk and hazards to populated areas.

By studying seismic activity, scientists can provide vital information for disaster preparedness and can also advance our understanding of Earth's inner processes. This knowledge helps mitigate the impacts of these natural events on human societies.