Warm-Up Write a paragraph describing what it is like to be in an earthquake. If you have never been in one, MAKE IT UP! Write about what you THINK it would be like. Use proper paragraph structure (from English) and sensory details to make the experience vivid.

Warm-Up Waves carry energy. List some examples of energy carried by waves.

Earthquakes Chapter 19

What is an earthquake? An earthquake is a natural vibration of the ground. Earthquakes are caused by: Movement along fractures (cracks) in the earth’s crust Volcanic activity

What forces affect earthquakes ? Earthquakes are caused by fractures. Fractures are caused by stress. Stress is the amount of force per area acting on a material. When stress exceeds the strength of the rock, an earthquake happens.

There are three types of stress: Compression—decreases the volume of a material Tension—pulls material apart Shear—twists a material Strain is the deformation of a material because of stress.

What is a fault? A fault is a fracture, or system of fractures, along which movement occurs. Faults form when stress is too great or applied too quickly.

What are the three types of faults? Normal fault Caused by horizontal tension of rocks being pulled apart. Movement is partly horizontal, partly vertical. Movement extends the crust.

Reverse fault Caused by horizontal compression of rocks being pushed together. Movement is partly horizontal, partly vertical. Movement shortens the crust.

Strike-slip fault Caused by horizontal shear of rocks sliding past each other. Movement is horizontal. Ex. San Andreas fault in California

What happens in the ground during an earthquake? During an earthquake, there are vibrations in the ground called seismic waves. The place where seismic waves start is called the focus of the earthquake.

The place above the focus, on the surface of the earth, is called the epicenter. There are three types of seismic waves.

What are the types of seismic waves? Primary waves (P-waves) Squeeze and pull (compress and stretch) rocks. Occur inside the earth’s interior. Secondary waves (S-waves) Move rocks up and down. Occur inside the earth’s interior. Surface waves Move rocks up and down as well as side to side. Occur on the surface of the earth.

What do seismic waves tell us about the earth’s interior? Seismic waves travel differently through different materials. P-waves refract (bend) when they reach the core. S-waves cannot go through the core because they cannot travel through liquid. This shows us that the layers of the earth have different densities. The time it takes seismic waves to travel through the earth tells us how thick each layer is.

How do we detect seismic waves? A seismometer is a device used to measure vibrations caused by earthquakes. Seismometers measure: Intensity of P-waves Intensity of S-waves Intensity of surface waves Time

Seismometer Demo In groups of three, get out one piece of paper and a pencil to share. Have one person lightly hold the pencil so that it is barely touching the paper. Have another person gently pull the paper so the pencil is making a straight line. Have the third person shake the table back and forth.

It takes three seismometers to find the epicenter of an earthquake. The place where the three circles overlap is the epicenter.

The time of an earthquake can be measured using a time-travel graph. P-waves travel faster and arrive first. S-waves travel slower and arrive last. The travel time is subtracted from the arrival time to find the time the earthquake occurred.

Earthquake magnitude (intensity) is measured on the: Richter scale – based on the size of the largest waves generated by the quake. –Increases by factors of 10 »Ex: A magnitude 7 earthquake is 10 times stronger than a magnitude 6. Moment magnitude scale – accounts for the size of the fault rupture, amount of movement, and rock stiffness Modified Mercalli scale – rates the type of damage caused by the earthquake.

What are the main earthquake hazards? Structural failure Land and soil failure Liquefaction is when solid earth is shaken until it acts like a liquid. Can cause landslides and sinking of structures. Fault scarps—vertical offset in the land Tsunami—large ocean waves caused by earthquakes