DO NOW REVIEW FROM BEFORE THE VACATION

1- Name the three type of plate boundaries, describe their direction of movement and what they create.

2- Explain what causes the plates to move around Earth.

Convergent – plates come together and form mountains, volcanos and trenches.Divergent – plates move apart and cause the sea-floor to spread and create new oceanic crust.Transform – plates move parallel (side by side) and create earthquakes and faults (cracks).

Convection currents within the mantle (asthenosphere) cause the plates to move. This is occurs as hot material rises and the cooler material sinks causing a circular flow.

Aim: What is an earthquake?

Do now: In your notes, explain where most earthquakes occur and Why?

Japan

I. Earthquakes

- are vibrations in the crust caused by moving crustal plates.

California

A.Focus - the origin (starting point) of the earthquake underground.

B. Epicenter – the location on the surface directly above the focus.

II. Causes of Earthquakes• the release of potential energy

stored in rock.

• energy is released in all directions

A. Elastic Rebound Hypothesis

- Deformation of rocks (stressing/bending) cause them to build up pressure (energy).

- When they break, the stored energy is released which results in the vibrations.

Closure:Why would someone think that mostearthquakes cause little damage and littleloss of life?

- Because most occur in areas that are not populated by people or cities.

Tokyo, Japan

AIM: How are Earthquakes Measured?

Do now:

If you were asked to measure a recent Earthquake, what information/ observations/data would you try to use?

I. Measuring Earthquakes

• Seismology – the study of earthquake waves (energy).

• Seismographs – instruments that record earthquake waves (energy).

*Seismos = earthquake

• Seismogram – a graph produced by recording the ground motion on a seismograph.

Creation of Seismogram

• Richter Scale: Measures the magnitude (strength) of an earthquake from the seismogram.

II. Types of Seismic Waves (earthquake waves)

epicenter

• created at the start of the earthquake.

What do you notice about the

waves in the diagram?

• The waves motion through Earth has helped scientists theorize about the inside of Earth and it’s structure.

A. Body Waves- Travel through the Earth’s interior.

1. P-waves (Primary/Compression Waves)

- push-pull waves that compress and expand

the ground in the direction that the waves travel.

How would you describe the motion of this wave?

2. S-Waves (Secondary/Transverse Waves)

- move the ground at right angles (up and down)to the direction that they travel.

How would you describe the motion of this wave?

P- Wave S-Wave

-Travels through solids and liquids.

-Travel Faster

-Arrives First

- Cannot go through Liquids.

-Travel Slower

-Arrives Second

P & S Wave Animation

B. Surface Waves –seismic waves that travel along the Earth’s outer layers (crust).

- Follow P and S waves

- Most destructive since they are on the surface

China

C. Aftershocks and Foreshocks• movements of the crust that follow a

major earthquake called aftershocks.

• small vibrations called foreshocks come before a major earthquake.

Anchorage, Alaska

III. Earthquake Zones

The “Ring of Fire” is the area that surrounds the Pacific Plate which is marked with volcanoes and earthquakes.

Aim: How do we locate Epicenters?

Based on the diagram, how many seismograph station locations are necessary to find the epicenter of an earthquake?

I. Locating an Earthquake Epicenter

• The difference in arrival times of P and S waves help locate the epicenter.

• The greater the difference, the greater the distance to the earthquakes epicenter.

Take a worksheet from the top bin

to practice subtracting P and

S wave times.

II. Distance to Epicenter (with one wave)

Using the ESRT page 11 we can translate the time into a distance.

… we can also use the same ESRT page to translate a distance into a time.

Examples:

1)A P-wave takes how long to travel 2600 km?2)An S-wave travels how far in 4 min?3)After 8 min and 20 sec. a P-wave travels?4)An S-wave travels 4.0 x 103 km in…

Get an Earthquake P and S wave Travel Time worksheet from the

top back bin.

Work on questions 1 - 8 ONLY!

Ex: S-wave – P-wave = 00:04:45

1) Use the time axis to mark off this difference in time.

2) Match the P and S wave lines with the marks you made.

3) Read down from this intersection to find the equivalent distance.

“Spread Technique”

• III. Distance to Epicenter (with two waves)

Complete the worksheet

IV. P- Wave Travel Time (or s-wave travel time)

-Use the distance from the previous step to find the travel time.

V. Origin Time-The origin is when the earthquake began. (start)

- Subtract the arrival time from the travel time

Origin (start) Travel Time Arrival (end)

V. Epicenter Location• Data from three or more

seismographs must be used to find the exact location of an earthquake epicenter. Epicenter

- Use the distance to epicenter value and a protractor to draw these circles.