LEARNING TARGET: I will be able to compare and contrast p-waves, s-waves and earthquake surface waves during today's class.

WORDS O' THE DAY:

• Primary (p) waves - Travel through all types of material and arrive first.
• Secondary (s) waves - Only travel through solid rock (not liquids of any sort) and arrive later
• Surface waves - Only travel along the surface of the earth-- they arrive LAST but are most destructive
• focus - The location of an earthquake inside the Earth
• epicenter - The point on the Earth's Surface directly above an earthquake

WORK O' THE DAY:

Ocean Wave Test Returns!

Did you check to see if:

• Your water heater is bolted to the wall?
• Your home was bolted to its foundation?

Why do we care?

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We'll get back to MMI and the qualitative analysis of earthquake waves on our community tomorrow-- but today we'll dive into the physics of earthquake waves --- This IS a unit on waves after all!

 

It it important that we understand that earthquakes occur when:

1. Segments of the Earth's crust slide against each other
2. Segments of the Earth's crust collide
3. Segments of the Earth's crust pull apart
4. Magma moves through and/or under the Earth's crust-- especially relating to volcanic events

You may have noticed that when an earthquake happens we very often hear about the "epicenter". What is that?

Hmmmmm.. epicenter is different from the "focus". What do you suppose the focus of an earthquake might be?

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Introducing earthquake waves!

Unlike water waves, earthquake waves come in three different flavors:

1) Primary Waves (p-waves)

Primary waves move through all types of material inside the earth... solid and liquid. That means they move through the dense rock of the crust, the liquid water in the oceans, the sorta squishy-not-quite-solid-but-not-quite-liquid rock of the mantle, the liquid rock of the outer core and the incredibly dense, solid rock of the inner core.

Secondary waves move only through solid rock

Surface waves travel ONLY along the surface of the Earth

Let's take a gander at THIS to help us visualize Primary, Secondary and Surface Waves (We won't worry about the differences between "Love" waves and "Raleigh" waves, to us they'll both just be Surface waves)

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Here's an interesting thought:

The federal government has *finally* (after many years of prodding) decided to fund an "early warning" system for earthquakes.

Here's how it works:

We all (I think?) have experience with those "Silver" or "Amber" alerts on our phones. They ring with a certain sorta ring tone and tell us that one of those alerts is in progress.

Imagine a different sort of ring tone that indicates that an Earthquake has ALREADY happened.

Additionally, there may be (I'm not sure about this one so we'll do a wee bit o' research here) a text msg that says something along the lines of:

"A major earthquake has occurred along the full length of the Cascadia Subduction Zone. You have no more than 45 seconds-- find shelter immediately. If you are driving a motor vehicle pull over at once -- away from any sort of unsafe structures."

 

From what you know of waves (so far), how can we have an early warning of an earthquakes' arrival if the first indication we have that an earthquake has occurred is when we feel the ground shaking?

 

Let's have a student/colleague lead the conversation here...

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No fair peeking!!!

 

 

 

The answer is:

Earthquake energy is carried away from the Cascadia Subduction Zone (or any other place an earthquake occurs) by (wait for it....)

 

wait for it....

 

Earthquake Waves!

Here's a curious enigma:

We've had to the tech to do this for at least 10 years. Do a quick bit of research on your chromies and see if you can find out how much this 'early warning' system actually costs (I don't think it's that much in the scheme of things)

Why did it take so long?

Japan 2011 - Subduction Zone Event