Earth Space Science Chapter 8

sunday 11.10.26

What is a fault?

A fracture in Earth where movement has occurred.

What is an epicenter?

The location on Earth's surface directly above the focus.

What is a focus?

The point inside Earth where an earthquake begins.

What is an earthquake?

The vibration of Earth caused by a rapid release of energy within the lithosphere.

What is elastic rebound?

When deformed rocks suddenly snap back toward their original shape, releasing stored energy.

What causes most earthquakes?

Stress builds up in rocks along a fault until they suddenly break or slip, releasing energy.

What is elastic energy?

Energy stored in rocks as they bend or change shape.

How does elastic energy cause earthquakes?

Stored energy is suddenly released when rocks slip along a fault, creating seismic waves.

What are foreshocks?

Smaller earthquakes that occur before a major earthquake.

What are aftershocks?

Smaller earthquakes that occur after a major earthquake.

What is fault creep?

Slow, gradual movement along a fault.

What fault caused the 1906 San Francisco earthquake?

The San Andreas Fault.

Why was the 1906 San Francisco earthquake important to scientists?

Studying it helped scientists develop the elastic rebound hypothesis and understand earthquake causes.

When can foreshocks occur?

Days or even years before a major earthquake.

What are seismic waves?

Waves of energy that travel outward from an earthquake's focus.

What are the two main categories of seismic waves?

Body waves and surface waves.

What are body waves?

Seismic waves that travel through Earth's interior, including P waves and S waves.

What are P waves?

The fastest seismic waves, which compress and expand material.

What can P waves travel through?

Solids, liquids, and gases.

How do P waves move particles?

Back and forth, parallel to the direction the wave travels.

What are S waves?

Slower seismic waves that shake particles at right angles to the direction of travel.

What can S waves travel through?

Only solids.

What are surface waves?

Seismic waves that travel along Earth's surface.

Which seismic waves are the slowest and most destructive?

Surface waves.

In what order do seismic waves arrive?

P waves first, S waves second, surface waves last.

What is a seismograph?

An instrument that records seismic waves.

What is a seismogram?

The recording of seismic waves made by a seismograph.

What is earthquake magnitude?

A measure of the size of an earthquake or the energy released at its source.

What is earthquake intensity?

The amount of shaking and damage at a particular location.

What is the difference between magnitude and intensity?

Magnitude measures earthquake size; intensity measures shaking and damage at a location.

What does the Richter scale measure?

Earthquake magnitude based on the amplitude of the largest recorded seismic wave, accounting for distance.

How much does wave amplitude increase for each whole number on the Richter scale?

10 times.

What scale is most widely used today to measure earthquakes?

The moment magnitude scale.

How does the moment magnitude scale measure earthquakes?

Using fault movement, the area of the fault that slipped, and rock strength.

Why is the moment magnitude scale preferred?

It estimates earthquake energy more accurately, especially for large earthquakes.

What does the Modified Mercalli scale measure?

Earthquake intensity based on shaking and damage, from I to XII.

What is the purpose of a travel-time graph?

To find the distance to an earthquake's epicenter using P-wave and S-wave arrival times.

What does a larger gap between P-wave and S-wave arrival times mean?

The epicenter is farther away.

How many seismic stations are needed to locate an earthquake's epicenter?

At least three.

How does triangulation locate an earthquake?

Draw circles around three seismic stations using their distances to the epicenter. Where all three intersect is the epicenter.

What factors determine how much damage an earthquake causes?

Strength and duration of shaking, ground conditions, and building materials and design.

Why might a smaller earthquake cause more damage than a larger one?

It may occur near a populated area, on soft ground, or where buildings are poorly constructed.

What is a tsunami?

A series of ocean waves caused by a sudden displacement of water, often from an underwater earthquake.

What happens to a tsunami as it approaches shore?

It slows down and increases in height, causing coastal flooding.

What is liquefaction?

When water-saturated soil loses its strength and behaves like a liquid during an earthquake.

What are examples of liquefaction damage?

Buildings sinking or tilting, bridges collapsing, and underground tanks or pipes rising.

What are the five major earthquake hazards?

Seismic shaking, liquefaction, landslides, mudflows, and tsunamis.

What is a seismic gap?

An area along a fault where no earthquake activity has occurred for a long time.

How can earthquake damage be reduced?

Assess earthquake risk, construct earthquake-resistant buildings, and follow safety precautions.

What are Earth's three layers based on composition?

Crust, mantle, and core.

What is the crust?

Earth's thin, rocky outer layer.

What is the difference between oceanic and continental crust?

Oceanic crust is thinner, denser, and basaltic. Continental crust is thicker, less dense, and granitic.

What is the mantle?

A thick layer of solid, hot rock beneath the crust, mostly made of peridotite.

What is Earth's core made of?

Mostly iron and nickel.

What are Earth's five layers based on physical properties?

Lithosphere, asthenosphere, lower mantle, outer core, and inner core.

What is the lithosphere?

Earth's rigid outer layer, made of the crust and uppermost mantle.

What is the asthenosphere?

A soft, weak layer of solid rock beneath the lithosphere that can flow slowly.

What is the lower mantle?

A stronger, solid layer of hot rock that can flow gradually.

What is the outer core?

A liquid layer of iron and nickel that generates Earth's magnetic field.

What is the inner core?

Earth's solid center, made mostly of iron and nickel.

Why is the inner core solid even though it is extremely hot?

Immense pressure keeps it solid.

What is the Moho?

The boundary separating Earth's crust from the mantle.

How did scientists discover Earth's internal layers?

By studying how seismic waves change speed and direction as they travel through Earth.

How do scientists know the outer core is liquid?

S waves cannot travel through it, and P waves bend and slow down when entering it.