Week 5 Earthquake Part1

Introduction to Earthquakes and Plate Boundaries

Overview

A comprehensive exploration of various earthquake types related to plate boundaries. Earthquakes occur due to the movement of tectonic plates, which can lead to various effects depending on their dynamics and the nature of the boundaries. The content will cover:

• The types of plate boundaries and the mechanisms behind them: forming, destroying, and lateral movement.

• Upcoming exam details will be provided next week to guide your studies.

Lecture Focus

The lecture will delve into the intricacies of earthquake types connected to plate tectonics, providing essential knowledge for understanding seismic activity:

• An introduction differentiating between natural earthquakes (caused by tectonic processes) and man-made earthquakes (induced by human activity such as mining, reservoir-induced seismicity from large dams, and geothermal energy exploitation).

• Discussion on current capabilities and limitations in earthquake prediction, including technologies like seismic monitoring and the challenges posed by the unpredictability of geological processes.

Understanding Plate Tectonics

A thorough understanding of the types of plate boundaries is critical:

• Spreading Centers: Where tectonic plates move apart, leading to the creation of new crust. Example: Mid-Ocean Ridges (e.g., the Mid-Atlantic Ridge)

  • Resultant earthquakes are typically small due to the hot, flexible rocks accommodating stress without significant energy build-up.

  • Notable example: Iceland, situated on the Eurasian and North American plate boundary, experiences volcanic activity from the Iceland plume, leading to relatively weak earthquakes despite its geological activity.

• Rifting: Occurs in places like the Red Sea, where intense geothermal activity, often from mantle plumes, causes the lithosphere to bulge and fracture, leading to the formation of rift valleys and new oceanic crust.

  • Associated earthquakes are generally minor in scale, predominantly affecting local geology.

Convergent Boundaries

Convergent boundaries are characterized by high seismicity due to plate collision, presenting three main collision types:

1. Oceanic-Oceanic: When two oceanic plates collide, one may subduct under the other, causing deep-sea trenches and triggering powerful underwater earthquakes.

2. Oceanic-Continental: Denser oceanic plates subduct beneath lighter continental plates. This process leads to recycling of materials and substantial energy release, resulting in significant seismic activity.

   • Earthquakes are categorized based on depth:

     • Shallow (<100 km depth): Occur at the surface of the overriding plate and within the upper section of the subducting plate.

     • Intermediate and Deep Earthquakes: Occur deeper in the downgoing plate where temperature conditions allow for stress accumulation without immediate release.

3. Continental-Continental: When two continental plates collide, this leads to intense pressure, forming mountain ranges and resulting in significant earthquakes.

Earthquake Energy and Depth

Understanding how energy is distributed during earthquakes is crucial:

• As energy travels through different layers of the Earth’s crust, its strength diminishes, affecting surface disturbance. Shallow earthquakes are particularly damaging due to the concentration of energy near the Earth's surface, leading to increased destruction.

Conclusion

Characterizing earthquakes based on plate tectonics is essential for predicting their behavior and potential impact on human populations and infrastructure. Ongoing studies and advanced models, such as those conducted by Earthscope, visualize stress accumulation and release during seismic events, contributing to a better understanding of earthquake dynamics and risk mitigation strategies.