Warm Up #14 What is an earthquake?

Ch. 3 Earthquakes and volcanoes Lesson 1: Earthquakes

Essential Questions What is an earthquake? Where do earthquakes occur? How do scientists monitor earthquake activity?

Earthquake ACTIVITY Earthquakes occur every day. On average, approximately 35 earthquakes happen on Earth every day. These earthquakes vary in severity. What causes the intense shaking of an earthquake? In this activity, you will simulate the energy released during an earthquake and observe the shaking that results. We will be using the Seismograph Activity Model. One student holds down the model on the plastic. Another student pounds on the desk 1 time while the teacher pulls the tape through. While the student is still holding the model down, another student will pound on the desk for about 5 seconds while the teacher pulls the tape through. Change directions of the model so pen is pointing down. While 1 student holds the plastic down, another student will shake the desk while the teacher pulls the tape through. What do you notice about the 3 different marks made?

What are earthquakes? Earthquakes – vibrations in the ground that results from movement along breaks in Earth’s lithosphere. The breaks are called faults. Greater the force applied to a fault, the greater the chance of a large and destructive earthquake. http://video.nationalgeographic.com/video/101-videos/earthquake-101 Whole Lotta Shakin’ – online resource Video

Where do Earthquakes Occur? Most occur in the ocean and along the edges of continents. Earthquakes result from the buildup and release of stress along active plate boundaries. Deepest earthquakes occur where plates collide Shallow earthquakes are common where plates separate or slide past each other Why do you think earthquakes tend to be deeper and more disastrous along convergent plate boundaries compared to earthquakes along divergent plate boundaries?

Where do Earthquakes Occur? What’s a fault? What happens when rocks move along a fault?

Where do Earthquakes Occur? Rock deformation – when a force is applied to rock along plate boundaries, the rock can change shape Fault – a break in Earth’s lithosphere where one block of rock moves toward, away from, or past another

Warm Up #15 What are the types of seismic waves?

Earthquake Focus and Epicenter Seismic waves – energy that travels as vibrations on and in Earth Focus – waves originate where rocks first move along the fault, as a location inside Earth Epicenter – the location on Earth’s surface directly above the earthquake’s focus What occurs when you drop a rock into a lake?

Types of Seismic Waves Wave motion, wave speed, and type of material that the wave travels through classify the type of seismic wave Primary waves – called P-waves that cause particles in the ground to move in a push- pill motion similar to a coiled spring Secondary waves – called S-waves, that are slower than P-waves and can cause particles to move up and down at right angles relative to the direction the wave travels Surface waves – cause particles in the ground to move up and down in a rolling motion, similar to ocean waves Only travel on Earth’s surface closest to the epicenter

Types of Seismic Waves

Mapping Earth’s Interior Seismologists – scientists that study earthquakes By comping measurements of the seismic waves to densities of different Earth materials, scientists have determined the composition of Earth’s layers Speeds of seismic waves depend on temperature, pressure, and chemistry of the rocks that the seismic waves travel through Tend to slow down through hot material

Locating an Earthquake’s Epicenter What’s the difference between a seismometer and a seismogram?

Locating an Earthquake’s Epicenter Seismometer – an instrument that measures and records ground motion and can be used to determine the distance seismic waves travel Seismogram – a graphical illustration of seismic waves that measures ground motion Triangulation is used to locate an earthquake’s epicenter Uses speeds and travel times of seismic waves to determine the distance to the earthquake epicenter from at least 3 different seismometers

Determining Earthquake Magnitude Richter magnitude scale uses the amount of ground motion at a given distance from an earthquake to determine magnitude Seismologists use moment magnitudes scale to measure total amount of energy released by the earthquake Energy released depends on size of fault that breaks, motion that occurs along the fault, and strength of the rocks that break during an earthquake Modified Mercali scale measures earthquake intensity based on descriptions of the earthquake’s effect on people and structures

Modified Mercalli Scale

Earthquake Risk How do seismologists evaluate risk?

Earthquake Risk Earthquake risk is figured out based on probability of one occurring, past earthquake activity, geology around a fault, population density, and building design in an area