Susan Barton

GCMS

7B Science

And

Defining Earthquakes

• Shaking and trembling of the earth’s crust.

• The waves travel in all directions

• More than 1,000,000 occur a year or one every 30 seconds

• Faulting is the most common cause

• Earthquakes continue until all the energy is used up

• TSUNAMIS- earthquake on the ocean floor: causing waves to become greater than 20 meters high

Seismic Waves

• FOCUS- underground point of origin

• EPICENTER- aboveground of origin; most violent shaking occurs at the epicenter

• The three main types of seismic waves are: P waves, S waves, and L waves

P Waves

• Primary waves

• Arrive first at the epicenter

• Can travel through solids, liquids, and gases

• They are push-pull waves

S Waves

• Secondary waves

• Can travel through solids, but NOT through liquids and gases

• Move in up-down motion

L Waves

• Surface waves

• Slowest moving seismic waves

• Travel on top of Earth’s surface

• Cause most of damage to Earth, because they bend and twist the surface

John Milne- 1893

• Seismograph-measures and detects seismic waves

• Seismogram- Paper record of waves

• Seismologist- scientist who study earthquakes

• Richter Scale- a scale that allows scientists to determine earthquake strength based on many readings

• 1-10 levels at which an earthquake is measured on amount of damage caused; Above a 6 is very destructive

VOLCANOES

• Volcano- place on Earth’s surface that allows magma and other material to erupt

• Magma- found beneath the Earth’s surface, it is liquid rock

• Lava- magma that reaches the Earth’s surface

Volcanic Fragments

• Volcanic Dust- less that 0.25 mm in diameter (flour)

• Volcanic Ash- more than 0.25 less than 5 mm (rice)

• Volcanic Bombs- few cm to several meters.

• Cinders- volcanic bombs the size of golf balls

Types of Volcanoes

• Cinder Cones- made of mostly of cinders; formed from explosive eruptions

• Shield- Made of quiet lava flows

• Composite- made up of alternating layers of rock particles; explosive eruptions, then quite lava flows

Volcanic Terminology

• Crater- funnel shaped pit, or depression at top of volcano

• Caldera- when a crater becomes too large, it collapses: also can form when the top of a volcano collapses or explodes

• Dormant- sleeping volcano

• Extinct- not known to have erupted in modern history

• Active- Erupts fairly regularly

Ring of Fire

Zones

• There are 3 zones:• Ring of Fire- Extends nearly all the way

around the edge of the Pacific Ocean• Mediterranean Sea- Italy, Greece,

Turkey• Iceland and Atlantic Ocean- Mid

Atlantic Ridge

EXTRA! EXTRA!

• Mount St. Helens is a volcano is Washington State

• San Andreas Fault in California

• New Madrid Fault is where we live