Lecture 21 more earthquakes

Norton Most earthquakes occur along the margins of tectonic plates... Earthquake “belts” 95% of energy from earthquakes comes from thin zones marking the edges of tectonic plates... Majo

Chapter 10:

Chapter 10: Chapter 10: Earthquakes Earthquakes (Part 2) (Part 2)

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Fig 10.22

W W Norton

Most earthquakes occur along the margins of tectonic plates

(Video simulations)

Earthquake “belts”

95% of energy from earthquakes comes from thin

zones marking the edges of tectonic plates

Major Earthquake “belts”

Some earthquakes are quite deep (up to 700 km or more) Deep quakes are found at subduction zones and are

confined to downgoing slabs of lithosphere

Active Volcanoes

Earthquakes & Plate Tectonics

-At divergent plate boundaries, plates move away from each

other at constant rates

the Red Sea

Normal Faults (Extensional Stress)

Earthquake “belts” & faulting styles

At convergent plate boundaries, oceannic plates come together forming subduction zones Example: Peru-Chile Trench

Deep Earthquakes in Subduction Zones

Earthquake “belts” & faulting styles

Where converging plates are bothmade of continental crust, they collide, forming

Earthquakes & Plate Tectonics

-At transform boundaries, plates slip pass each

other at constant rates

Fig 10.00

U.S Geological Survey

Fig 10.24

W W Norton

Major Tectonic Environments of Earthquakes

Summarizing…

 P-waves

- Travel faster

- Move through both solids and liquids

 S-waves: Shear waves

- Travel slower

- Only travel through solids

 Information carried by these waves is used to:

-Locate the focus of the earthquake.

-Calculate the earthquake magnitude.

EARTHQUAKES GENERATE TWO TYPES OF INTERNAL

OR “BODY” WAVES

Types of Earthquake Waves

“Body waves”

P-waves (“P” for primary)

S-waves (“S” for secondary)

Expansion/compression:

push/pull motion

Shear:

side-to-side motion

“Surface Waves” travel at the Earth’s surface

travel in the Earth’s interior

Fig 10.13ef

W W Norton

Love Waves

In summary: Types of seismic waves

S-wave

Surface-wave

Motion produced by the

different wave types

P-wave

IN CLASS EXERCISE

Observe the following objects as I

drop them on the floor in class:

4) Which of these material properties

accounts for earthquakes?

Fig 10.02

J Dewey, U.S Geological Survey

Next time:

Locating EarthquakesEarthquake magnitudes

Human Consequences