E3.P3XB Unit

Plate Boundaries and Earthquakes

Types of Plate Boundaries

• Divergent

• Transform

• Convergent

Assignment

• Students are to draw a table

Boundaries Corresponding Faults

Surface Features

Examples

Convergent

Transform

Divergent

What are Earthquakes?

Red Book Chapter 8 Section 1

Where Do Earthquakes Occur?

Where do Earthquakes Occur?

• Seismology- the study of Earthquakes• According to the previous map, where do

Earthquakes occur?

• Answer: Earthquakes occur along fault lines due to the continuous movement of the Earth’s tectonic plates

The Largest Quakes occur due to the Pacific Plate!

• What phenomenon causes the Earth’s Tectonic Plates to be in constant motion?

• Answer: Convection Currents of the Mantle

What Causes Earthquakes?

• The push, pull, and grinding of tectonics plates against one another frequently causes deformation of those plates

• Deformation- the change in the shape of the rock as a response to tectonic motion– There are two types of deformation

• Deformation1. Plastic Rebound• The plate is deformed and takes on a new shape– As if you were molding clay

• Plastic Rebound does not cause Earthquakes

2. Elastic Rebound• The plate is deformed to a “breaking point” and snaps

back into its original shape or position with a great release of energy

• Elastic Rebound causes Earthquakes

Elastic Rebound has been known to leave evidence such as displaced fence lines

All Are Earthquakes the Same?Plate Motion/

BoundaryFault Type Surface

FeaturesEarthquake

Characteristics

Transform Strike-Slip “San Andres Fault”

Moderate with Shallow Waves

Convergent Reverse/ Normal Mountains and Volcanoes

Strong with Deep Waves

Divergent None, there is no contact

Mid-Ocean Ridges

Weak with Shallow Waves

How Do Earthquakes Travel?• Seismic Waves- Waves of energy that travel

through the Earth– Primary P Waves– Secondary S Waves

• Body Waves– Waves that travel in the interior of the Earth – P and S waves are Body Waves

• Surface Waves– Waves along that surface of the Earth that move

the ground just like the ocean waves

Assignment1. Where do Earthquakes occur?2. How do convection currents play a role in

causing Earthquakes?3. What form of deformation causes

Earthquakes and offsets fence-lines?4. Name the plate boundaries/motions from

weakest to strongest pertaining to Earthquakes.

5. Why are Surface Waves more destructive to buildings than P and S waves?

Measuring Earthquakes

Chapter 8 Section 2

Locating Earthquakes• Seismographs- measure seismic waves• Seismogram- unit of measurement as

recorded by a seismograph

What is the name of the Scientist who studies Earthquakes?

• Seismologists study Earthquakes• Earthquakes happen with Elastic Rebound– The SNAP!

• The seismograph starts recording at the start of the quake– The more movement, the bigger the quake!

• By comparing the P and S Waves on the machine, exact start time can be determined

Which Types of Wave Arrives First?P-Waves arrive first. P for Primary! They are faster because they travel through all types of matter: Solid, Liquid, and Gas

• Focus- Earthquake’s starting point in the body of the Earth

• Epicenter- location on the crust directly above the focus– Seismographs can also help to find the focus

• Scientists can see how far the Earthquake has traveled in a certain amount of time to locate the epicenter

Finding the Epicenter

1. Circles are drawn around each effected seismograph station

2. Circles for each station have an overlapping point

3. When all circles are drawn, they all intersect at only one point.

This spot is the Epicenter!

Measurement Methods• Richter Scale– Invented by Charles Richter – 1.0-10.0, bigger numbers for bigger damage

• Momentum Magnitude– Records amount of energy released– For every 1 pt on the Richter scale the energy

released is 31.7 times moreIf an Earthquake is measured at a 3.5 Richter, what

is the Momentum?3.5 x 31.7 = 110.95 units

Richter X 31.7 = Energy Units

Assignment1. What is the difference between seismograph

and seismogram?2. At least how many seismograph stations are

need to locate an epicenter?3. What is the difference between the

Momentum Magnitude and the Richter Scale?

4. If an Earthquake is 7.0 on the Richter Scale, what is if on the Momentum Magnitude?

5. Which types of waves travel faster? Why?

Earthquakes and Society

Chapter 8 Section 3

Earthquake Hazard• Earthquake Hazard- How prone an area is to

receive Earthquakes– Determined by past and present seismic activity

Find where we live. Do we have a high or low hazard level?

Earthquake Forecasting• What do you think it means to Earthquake

Forecast?• Answer: The practice of predicting when and

where Earthquakes will occur!• Seismologists have discovered patterns in

Earthquake activity that allows for predictions• Fault zones are closely monitored for seismic

activity

Worldwide Earthquake Frequency ChartDescription Richter Scale Average Annual

OccurrenceCatastrophic 8.0 or Higher 1

Major 7.0-7.9 18

Strong 6.0-6.9 120

Moderate 5.0-5.9 800

Light 4.0-4.9 About 6,200

Minor 3.0-3.9 About 49,000

Very Minor 2.9 or Less About 365,000

Which type of Quake is less prevalent? Most prevalent?

• The Gap Hypothesis – active faults with few quakes are likely to have strong quakes

• Seismic Gaps – areas along a fault where few quakes have occurred

• Seismic Gap Hypothesis helped seismologists determine the time, place, and strength of the 1989 San Fran Quake

Earthquakes and Buildings

• When the ground shifts, the center of gravity for a building shifts, and the building falls

• Earthquake resistance buildings:– Mass Damper- weight on roof to stop movement– Cross Braces- strengthen the floors– Flexible Pipes- prevent breaks– Active Tendon- base weight to stop movement– Base Isolators- absorb seismic waves

Mass Dampers can be metal weights or water filled tanks

Are You Prepared?

• Before Shaking Starts– Put heavy objects on low shelves• Less likely to hit anyone if they fall

– Designated meeting spots• Communication lines will be out

– Stashes of flashlights, water, canned foods, batteries, first aid, fire extinguisher

• When Shaking Starts– Crouch/lay under sturdy table/desk– Cover your head with your hands– Remain in your vehicle

• After Shaking Stops– Be wary of aftershocks and fire, glass, other hazards– Meet family at designated area

Assignment1. How is an area’s Earthquake Hazard determined?2. Describe three ways to reinforce buildings.3. Name four items to store in case of an

Earthquake.4. Where is the safest place to be during an

Earthquake? A highway, times square, or the top bowl at Ford Field. Why?

5. What is gap hypothesis and how does it forecast Earthquakes?

6. Draw the 3-part Earthquake safety procedure.

The Impact of Earthquakes

Natural Disasters

• Earthquakes can cause many disasters such as:– Tsunamis– Landslides/Mudslides– Avalanches– Fires from gas leaks– Floods

WEIRD!

• We know that many quakes occur on the West Coast of the US, but did you know that the Mid-West and East Coast can feel them, too?!

• In 1811, four HUGE quakes rocked Missouri, causing the Mississippi to run backwards. The waves traveled all the way to Boston and rang the church bells!

Assignment

• What are the disasters causes by quakes?• What is the safety procedure for both in cars

and in builds?

• Additional Worksheet