Earthquakes and Triangulation

Earthquakes

How many earthquakes are expected each year?

• Millions of earthquakes happen every year. Most are too weak to be felt.

• The National Earthquake Information Center records about 20,000 a year.

• That's about 55 recorded earthquakes a day!

What is an earthquake?

• The movement of Earth’s crust resulting from the release of built-up potential energy between two stuck lithospheric plates

Parts of an Earthquake

• Focus: point below the surface where the rock breaks causing the earthquake

•  Fault: area where tectonic plates meet

• Epicenter: the point on the surface right above the focus

Seismic Waves

• Waves that carry energy of an earthquake away from the focus

• Body Waves

  • P-waves (Primary): fastest, travel through solids and liquids, compress materials they pass through.

  • S-waves (Secondary): travel through solids in up and down motion

•  Surface waves: slowest, reach the surface. Cause the most damage.

Seismic Waves

• Measured with seismographs

Multiple Choice

A point on Earth’s surface right above the focus of an earthquake.

• Epicenter

• Heliocenter

• Hipocenter

• Staples center

Multiple Choice

Which type of seismic waves cause the most damage?

• P-waves

• S-waves

• Surface waves

• Tsunami waves

How is an Epicenter Located?

• Seismic Waves can identify an epicenter

  • Measure the time between P and S waves and use a formula to determine how far away it is

  • Data from at least 3 Seismographs are needed

  • Longer time in between P and S waves= epicenter is farther away

How is an Epicenter Located

Grade 8 Ohio| Lesson 4.1

How is an Epicenter Located?

• Graphs of P and S Waves can get even more specific

  • The closer P and S waves are on a graph, the closer that spot is to the epicenter ​

Multiple Choice

True or False: Geologists can pinpoint the epicenter of an Earthquake from Just two seismographs

• True

• False

Multiple Choice

These are the first waves released during an earthquake

• S waves

• Surface Waves

• P waves

Multiple Choice

When scientists map the location of earthquakes, where do they find that most earthquakes happen?

• middle of tectonic plates

• in the core of the earth

• only near mountains

• at plate boundaries

Multiple Choice

Where is the epicenter for this earthquake located based on triangulation?

• A

• B

• C

• D

Multiple Choice

Where does an earthquake start?

• focus

• epicenter

• upper mantle

Multiple Choice

What method do seismologists use in locating an epicenter?

• Focus Group Discussion

• Interview

• Observation

• Triangulation

Open Ended

Would you predict more earthquakes in areas where the Earth’s tectonic plates are moving towards each other or where the plates are moving apart? Explain your reasoning.

Open Ended

Why would geologists need seismic data from three stations in order to calculate the epicenter of an earthquake? What would happen if they only used two stations?