Name-Class- Roll No-

Earthquakes Most Earthquakes (95%) occur along PLATE BOUNDARIES Why do they occur?

Ring of Fire 80% of the world’s earthquakes occur in a ring that borders the pacific ocean 80% of the world’s earthquakes occur in a ring that borders the pacific ocean This ring is called “ the Ring of Fire ” This ring is called “ the Ring of Fire ”...Not...

IN BC...

How they begin... An Earthquake starts at a location inside the Earth called a “focus” (foci) An Earthquake starts at a location inside the Earth called a “focus” (foci) Release of energy starts here...

EPICENTRE The “epicentre” is the point on the EARTH’s SURFACE directly above the focus. It is not the center where the Earthquake starts!

DEPTHS of EARTHQUAKES... CLASSIFICATIONDEPTH OF FOCUS Shallow Focus0 – 70 km Intermediate Focus70 – 300 km Deep Focus> 300 km Most Earthquakes have focus less than 100 km deep About 3% of quakes

SEISMIC WAVES Seismic waves are the vibrations (waves) of energy released by a quake! THERE ARE THREE TYPES OF WAVES BODY WAVES SURFACE WAVES P- waves S- waves L- waves

BODY WAVES (P and S) P WAVES (P= Primary) - Fastest (6 km/s) - Causes ground to squeeze and stretch like a spring! - Can travel though solids, liquids, and gases

BODY WAVES (P and S) S WAVES (S= Secondary) - Slower (3.5 km/s) - Causes ground to SHAKE - Can travel though solids (not liquids) These waves are usually larger...do the most damage!

Travelling Through Layers

P and S Waves P S S No S Waves (liq)

SURFACE WAVES (L) L WAVES (Surface waves) - Slowest! - Travel along Earth’s surface (like pond ripples) - Causes ground to move in “rolling motion”

Measuring Earthquakes “Seismometers” Devices that measure the amount of ground motion Produces a “seismogram”

Seismogram 10 sec Tell us... How long it lasted, how fast waves travelled, amount of ground shaking, magnitude...

Ancient Chinese Seismometers

7.8 magnitude (China)

VOLCANOES We will look at 3 types of volcanoes (1) Composite Volcanoes (2) Shield Volcanoes (3) Rift Eruptions

(1) Composite Volcanoes Cone-shaped volcanoes (layers build up) Usually found near “subduction” zones (converging plates) Ex: Mt St. Helen’s

Mt St Helen’s, Washington

(2) Shield Volcanoes These are the LARGEST volcanoes DO NOT occur at plate boundaries... They form over HOT SPOTS Usually occur in ocean basins (weak spot in lithosphere...magma breaks through)

Shaped like a “soldier’s shield” lying down

(3) Rift Eruptions Occur at “rifts” and “ridges” (divergent plates) “Fountains of lava” Not very destructive or violent Common along the Mid-Atlantic Ridge