What is an earthquake?

LO: I can use geographical terminology associated with tectonic

processes

Working in pairs answer the following questions:

• What are earthquakes?

• What do you understand by the words magnitude, epicentre and focus?

Key terms:• Earthquake: Shaking and vibration of the ground caused by

movements in the earths crust.

• Magnitude: The strength of an earthquake

• Epicentre: The point on the ground above the focus where the vibration is the greatest

• Focus: The point underground that shock waves travel out from

Epicentre and focus

How do we measure earthquakes?

LO: to understand the difference between the Richter scale and the

Mercalli scale

What is the difference between the Richter scale and Mercalli scale?

The Richter scale: Measures the intensity fo the earthquake

The Mercalli scale: measures the damage caused by the earthquake

The Richter scale

The Richter scale can be used to measure the magnitude (power) of a tremor using an instrument called a seismograph.

How are earthquakes measured?

It is a logarithmic scale which means that a size ‘6’ earthquake on the Richter scale is 10 times larger than a size ‘5’ and 100 times larger than a size ‘4’.

How does a seismograph work?

Richer scale task: Play the game…

• Guess the Richter scale

The Mercalli scale rates an earthquake's magnitude based on observations of the damage it causes on a scale of 1 to 12.

The Mercalli Scale

Items shake from shelves: scale 5

Buildings collapse: scale 10

1. Instrumental Detected only by seismographs 2. Feeble Noticed only by sensitive people. 3. Slight Resembling vibrations caused by heavy traffic. 4. Moderate Felt by people walking; rocking of free standing objects. 5. Rather strong Sleepers awakened and bells ring. 6. Strong Trees sway, some damage from overturning and falling objects. 7. Very strong General alarm, cracking of walls. 8. Destructive Chimneys fall and there is some damage to buildings. 9. Ruinous Ground begins to crack, houses begin to collapse and pipes break. 10.Disastrous Ground badly cracked and many buildings are destroyed. There are some landslides. 11.Very Disastrous Few buildings remain standing; bridges and railways destroyed; water, gas, electricity and telephones out of action. 12.Catastrophic Total destruction; objects are thrown into the air, much heaving, shaking and distortion of the ground.

The Mercalli scale

Use the descriptions on to produce a series of cartoons that show each of the categories of the Modified Mercalli Scale

Mercalli scale task:

Use the descriptions of the points on the Mercalli scale to draw pictures or cartoons, or find photos on the internet to show the destruction observed at each point on the scale.