Hi, my name is Mr. Lawledge.

And I'm excited to be learning with you today.

We're going to have a great time.

Today's lesson is measuring earthquakes.

And this is from the unit earthquakes.

How do they change the world? Our learning is challenging today, but I'm here to help and we can learn together.

Let's get started.

By the end of the lesson, you will be able to describe and explain how we measure earthquakes.

The key words we will be using today are focus or focus point.

Epicentre.

Seismic waves.

And magnitude.

The point inside earth's crust where the earthquake starts is called the focus or focus point.

The epicentre is the point on earth's surface directly above the focus of an earthquake.

Seismic waves are vibrations that travel through earth generated by an earthquake or an explosion.

Magnitude is a measure of the size of the seismic waves generated by an earthquake.

Some tricky words there.

Our learning today will be split into two parts.

The first part is where are earthquakes felt the strongest? The second part is how is the strength of earthquakes measured? So let's begin with our first section.

Where are earthquakes felt the strongest? Earthquakes are caused by plate movement underneath the earth's crust.

Remember, tectonic plates are the huge pieces of earth's crust that fit together like a jigsaw.

They move because they sit on top of earth melting, moving mantle.

Here we can see two tectonic plates moving in opposite directions.

The friction created as the tectonic plates move causes them to interlock.

This is where subsequent pressure is built up.

When that subsequent build tension or pressure is released, huge waves of energy known as seismic waves or shock waves are released.

This is what causes a sudden shaking of the ground, which is an earthquake.

Here we have our first check for understanding.

How do earthquakes occur? Is it A.

By severe weather? Is it B.

When tectonic plates deep below earth's surface build friction or pressure and then release? Or is it C.

Randomly? Pause the video now and have a go at answering that question.

Welcome back.

Did you answer B correctly? Earthquakes occur when tectonic plates deep below earth's surface build friction or pressure and then release.

Well done if you got that answer correct.

The point deep underground where the tectonic plates first break or slip is called the focus point.

We can see it here marked by the pink dot beneath earth's surface.

And you can also see there the seismic waves radiating out of the focus point.

Seismic waves radiate out from the focus point towards earth's surface.

Typically, seismic waves travel at speeds between one and 14 kilometres per second.

To put that into a little bit of perspective, to run 10 kilometres the other day, it took me almost an hour.

So seismic waves are travelling through earth's crusts extremely fast.

The point on the surface directly above the focus is called the epicentre.

This is where earthquakes are felt first by humans because the point on the earth's surface where we live.

Let's check our understanding here with a true or false question.

The point at which an earthquake felt first is called the epicentre.

Is that true or false? Pause the video now to answer that question.

Well done if you got that right.

That is true.

The point at which an earthquake is felt first is called the epicentre.

Can you justify your answer? Is it A.

The focus point is the point where earthquakes are felt first on earth's surface? Or is it B.

The epicentre is where earthquakes are felt first on earth's surface and this is where earthquakes are felt the strongest? Pause the video now to answer that question.

Welcome back.

Did you answer correctly? It is B.

The epicentre is where earthquakes are felt first on earth's surface, and this is where earthquakes are felt the strongest.

Remember, the focus point is where the tectonic plates first slip and where seismic waves radiates out of.

We have reached our first task today.

Can you annotate the diagram with the following labels.

Seismic waves, focus or focus point and epicentre.

Once you've completed that task, I'd like you to explain to your partner where earthquakes are felt the strongest.

Pause the video now to have a go at that.

Welcome back.

Did you annotate your diagram correctly to show seismic waves radiating out of the focus point? The epicentre on earth's surface, which is where the earthquake hits first, and also the focus point as the point where the tectonic plates first slip or release.

Did you tell your partner that the point on earth's surface above the focus is called the epicentre? This is where earthquakes are felt the strongest, and that's because it's where we live as humans.

Well done if you completed those questions correctly.

We're now onto the second part of our learning.

How is the strength of earthquakes measured? Let's begin.

The power or strength of an earthquake is called its magnitude.

An earthquake's magnitude is measured using instruments called seismographs.

Seismographs make a record of ground motion or the ground shaking caused by an earthquake.

Let's stop and check our understanding here.

What instrument is used to measure the strength of earthquakes? Is it A.

A thermometer? B.

A ruler? Or C.

A seismograph? Pause the video now and think carefully about that question.

Welcome back.

Did you answer C correctly? A seismograph is used to measure the strength of earthquakes.

Well done if you got that question correct.

Traditionally, the Richter scale was used to measure the magnitude of earthquakes once information had been taken from a seismograph.

The Richter scale measures the largest single tremor caused by an earthquake.

More commonly these days, scientists are increasingly using the Moment Magnitude scale.

The Moment Magnitude scale measures the total amount of energy released from an earthquake.

Here we can see, the higher the number on the Moment Magnitude scale, the stronger the earthquake.

And it ranges from one to 10.

Earthquakes with a one or two are very minor earthquakes, which are not really felt by people.

Earthquakes with a magnitude of four to six are minor to moderate earthquakes which may cause property damage, especially if they are six.

Earthquakes that are a seven upwards are all very serious earthquakes.

They may cause loss of life, extensive damage and destruction.

And nine on the Moment Magnitude scale is the largest recorded earthquake, with mass loss of life and destruction over a vast area.

The largest earthquake currently recorded was in Chile in 1960, which reached 9.

5 on the Moment Magnitude scale.

Let's stop and check our understanding again here.

Which two scales are used to measure the magnitude of earthquakes? We have A.

Weighing scales.

B.

The Richter scale.

And C.

The Moment Magnitude scale.

Remember, you're choosing two out of those three options.

Pause the video now to have a go at completing that question.

Welcome back.

Did you answer B and C correctly? The Richter scale and the Moment Magnitude scale are used to measure the magnitude of earthquakes.

While the Richter scale and Moment Magnitude scale both measure the strength of earthquakes, scientists also use the Mercalli scale to measure an earthquake's impact at its epicentre.

The Mercalli scale, which was introduced by a man called Giuseppe Mercalli, describes what would be felt and what, if any, damage would occur if you were there at the epicentre of the earthquake itself.

Here we can see it right on earth's surface.

So that's the impact on the earth's surface.

Similarly to the Moment Magnitude scale, the higher the number on the Mercalli scale, the stronger the earthquake.

This scale ranges from one to 12, which we'll talk about over the next few slides.

Earthquakes one to four here range from not felt at all to light.

During a four earthquake, the ground may shake slightly, walls may crack and parked cars might rock, sending off their alarms. A one earthquake would not be felt by people.

Earthquakes five to eight on the Mercalli scale range from moderate to severe.

So that's ranging from being felt by nearly everyone and glass shattering to definitely being felt by everyone, and severe damage to poorly built buildings and older structures.

Earthquakes nine to 12 on the Mercalli scale range from violent to extreme.

This ranges from severe damage to buildings to completely everything being destroyed.

These earthquakes are very dangerous and could potentially cause great loss of life.

That brings us onto our next task.

Complete the table for your own Mercalli scale, outlining what might happen during earthquakes of an intensity of one to four, five to eight and nine to 12.

So remember, you're looking at the effect or the damage of what would happen during those earthquakes.

Pause the video now to complete that task.

Welcome back.

Does your work include the following information.

Earthquakes with a one to four on the Mercalli scale.

You mostly wouldn't notice these earthquakes.

Some of the stronger ones would make things shake and some things might wobble or fall over.

So they're not very serious, those earthquakes.

Earthquakes with a five to eight on the Mercalli scale.

You would feel those earthquakes on the epicentre.

They may be frightening, and some things around you might break.

Some of the stronger ones might make buildings break.

And lastly, earthquakes with a nine to 12 on the Mercalli scale.

These would be very dangerous and would be frightening.

The strongest ones would break all the buildings and roads, and they would cause a lot of destruction.

There might even be loss of life there as well.

Well done if you answered those questions correctly.

And your work included similar information.

That takes us to the end of our lesson.

Let's quickly summarise today's lesson.

We have learned that the focus of an earthquake is deep underground.

Seismic waves radiate out from the focus point.

We've also learned that the epicentre is on the surface, directly above the focus and is where the earthquake is felt most strongly.

We've also learned the power of an earthquake is called its magnitude, and is measured on the Moment Magnitude scale.

So remember there, the Mercalli scale measures the impact on the surface of an earthquake and its epicentre.

Well done for all your hard work today.

And I hope to see you again for some more fantastic geography.