Seismic Waves and Earth's Interior

This page delves deeper into seismic waves and their behavior as they travel through Earth's interior. It also covers the concept of convection cells and provides practical information on interpreting seismograms.

Definition: Convection cells are the circular patterns that form in liquids and gases as a result of changes in temperature and density.

The page explains that S waves are absorbed in the outer core and refracted in the mantle. This behavior of seismic waves provides crucial information about Earth's internal structure.

Example: You can determine the closest seismogram to the epicenter based on the shortest time difference between P and S waves, and the arrival of P-waves first.

The page provides guidance on when to use the ES (Epicenter-Station) slide rule:

1. When finding the epicenter distance given the time difference between P and S waves.
2. When finding the epicenter distance given the arrival times of P and S waves.

Highlight: An earthquake produces waves, not the other way around. This is a crucial concept to understand in earth science.

The page also covers important concepts for exams:

• No P-waves or S-waves are received in the shadow zone because P-waves are refracted and S-waves are absorbed by Earth's core.
• Earth's interior has been classified into zones (crust, mantle, outer core, and inner core) based on evidence from earthquake seismic waves.

Earthquakes, Plate Boundaries, and Wave Characteristics

This final page focuses on the relationship between earthquakes, plate boundaries, and the characteristics of different types of seismic waves. It also provides practical information on earthquake calculations.

Highlight: Most earthquakes are concentrated in zones along plate boundaries. Volcanoes and earthquakes occur at all plate boundaries.

The page reiterates the differences between oceanic and continental crust:

• Oceanic crust is more dense and made of basalt
• Continental crust is less dense and made of granite

It then describes the motion of different seismic waves:

Vocabulary:

• S-waves move side to side
• P-waves' motion is a push and pull

The page provides a step-by-step guide for earthquake calculations:

1. Calculate P-wave and S-wave travel time if given epicenter distance
2. Calculate epicenter distance if given P and S wave travel time
3. Calculate the difference in arrival times between P and S waves

Definition: The asthenosphere is the plastic mantle layer, which allows for movement of tectonic plates.

This information is crucial for understanding the difference between convection currents and seismic wave behavior. While convection currents in the mantle drive plate tectonics, seismic waves provide information about Earth's internal structure and help locate earthquake epicenters.

Tectonic Plates and Continental Drift

This page introduces the concept of tectonic plates and their role in shaping Earth's surface. It covers the formation of Pangea, the characteristics of continental and oceanic crust, and the three main types of plate boundaries.

Definition: Pangea was the supercontinent that existed approximately 300 million years ago, where all continents fit together like a puzzle.

The page explains the differences between continental and oceanic crust, highlighting that continental crust is thicker and less dense, while oceanic crust is thinner and more dense. It then introduces the three types of plate boundaries:

1. Transform plate boundary: Where plates slide past one another.
2. Divergent plate boundaries: Where plates move away from each other.
3. Convergent plate boundary: Where plates collide.

Highlight: As the distance from the mid-ocean ridge increases, the age of the rock also increases. This is crucial evidence for seafloor spreading.

The page also touches on the concept of magnetic patterns on either side of mid-ocean ridges, which mirror each other and provide further evidence for plate tectonics.

Lastly, it introduces different types of seismic waves:

Vocabulary:

• P-waves: Travel through all materials
• S-waves: Travel through solids only
• Surface waves: Travel only on the surface

The page concludes by mentioning that three seismograph stations are needed to determine the location of an earthquake epicenter and introduces the concept of convection currents in the mantle.