Earthquakes Chapter 15 - Belmont ESC11

Chapter 15

Earthquakes and Plate Tectonics...

...what's the connection?

As with volcanoes, earthquakes are not randomly distributed over the globe

Figure showing the distribution of earthquakes around the globe

At the boundaries friction causes plates to stick together.

Figure showing the distribution of earthquakes around the globe

Earthquakes occur when built up energy causes them to break apart.

1

Where Do Earthquakes Occur and How Often?

? ~80% of all earthquakes occur in the Ring of Fire (most of result from convergent margin activity)

? ~15% occur in the Mediterranean-Asiatic belt

? remaining 5% occur in the interiors of plates and on spreading ridge centers

? more than 150,000 quakes strong enough to be felt are recorded each year

S.2

Where do earthquakes form?

ADD ARROWS TO DIAGRAM

S.3 Figure showing the tectonic setting of earthquakes

Where do earthquakes form?

Figure showing the tectonic setting of earthquakes

What is the Elastic Rebound Theory?

?Explains how energy is stored in rocks ?Rocks bend until the strength of the rock is exceeded ?Rupture occurs and the rocks quickly rebound to an undeformed shape ?Energy is released in waves that radiate outward from the fault

S.4

2

What is an Earthquake?

Ground movement caused by the sudden release of seismic energy due to tectonic forces.

S.5a

The Focus and Epicenter of an Earthquake

? The point within Earth where faulting begins is the focus or hypocenter

? The point directly above the focus on the surface is the epicenter

S.5b

Fault Traces Southern

Vancouver Island

Fault Traces Southern

Vancouver Island

Wrangellia

Pacific Rim Terrane

Crescent Terrane

3

What are Seismic Waves?

? Response of earth material to the arrival of energy fronts released by rupture

? Two types: ? Body waves ? P and S ? Surface waves ? R and L

TwPo TWypaesvoef Bsody Waves

P-Waves

Body Waves: P and S waves

S.6

P or primary waves

? fastest waves

? travel through solids, liquids, or gases

? compressional wave, material movement is in the same direction as wave movement

S or secondary waves

? slower than P waves ? travel through solids only

? shear waves - move material perpendicular to wave movement

TwSo TWypaesvoef Bsody Waves

S-Waves

4

Surface Waves: R and L waves

Surface Waves ? Travel just below or along the ground's surface ? Slower than body waves ? Rolling and side-to-side movement ? Especially damaging to buildings

S.7

Functioning of Seismograph

Two Common Types of Surface Waves

How is an Earthquake Recorded?

Seismographs record earthquake events on a seismogram.

S.8

At convergent boundaries, focal depth increases along a dipping zone called a Benioff zone

5

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