Chapter 6 – Earthquakes Part 3

Earthquake Destruction.

The largest quake recorded to date has been the 1960 Chilean quake - 8.6. The largest North American quake is the 1964 Alaskan quake - 8.4 and it lasted 3-4 minutes with 28 aftershocks, 10 at magnitude 6.

What does it all add up to?

Factors Affecting Structural Damage

1. The amplitude of the waves.

2. The duration of the quake.

3. The type of material the structures are build on.

4. The design of the structure.

See page 166.

Seismic Waves and Liquefaction

Liquefaction is the liquification of seemingly solid ground. It results when unconsolidated material like glacial till become saturated by water.

The shaking causes the materials to mix with the water creating a “soup”.

The result is sinking buildings and rising tanks.

Tsunami Not Another A Japanese Car Seismic sea waves

It is Japanese for harbour wave. They result from the vertical displacement of the ocean floor.

The energy is transmitted to the water. In the open ocean, they may not appear to be very large, but a they approach land, water piles upward, creating huge towering waves.

See page 169-170

Landslides and Ground Subsidence

It goes without saying that if the ground shakes, landslides will result.

Ground subsidence occurs when water replaces land due the slipping of large land masses into lake or the ocean.

Fire!

Identify some probable sources of fire duing or after a destructive quake.

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The Earth’s Interior (Again!)

What can earthquakes tell u about the earth’s interior?

Since drilling limits how deep we can go, seismic waves can tell u a lot.

The characteristics of p and s waves, like their speeds and what they travel through.

Knowledge of the focus and multiple seismic readings of quake have given us the following structure of the earth:

Four Layers1. The crust – outer most layer ~100 km

thick.2. The Mantle – rocky layer beneath the

crust, with areas of molten rock ~ 2885km thick.

3. The Outer Core – molten layer composed mainly of iron and nickel ~ 2270 km thick.

4. The Inner Core – solid metal, iron and nickel ~ 1216 km thick

Just Call Me Moho!

The Mohorovicic Discontinuity, the boundary between the crust and the mantle, was found using seismic waves.

Another zone discovered was the p-wave shadow zone where p-waves tend to die out. This results because of sudden changes between the mantle and outer core. The p-waves bend and change direction, causing a zone between 105 and 140 degrees. See p.173

Asthenosphere and Lithosphere

The asthenosphere is the plastic upper layer of the mantle capable of flowing.

The lithosphere is the solid cool layer above the asthenosphere which includes the crust.

See page 175.

Now sketch it all together!