Earth's outermost rigid rock area, the crust, is called the lithosphere. The lithosphere is split into 7 major plates.
  • African
  • Eurasian
  • Indian-Australian
  • Antarctic
  • Pacific
  • North American
  • South American

The 7 plates float on the asthenosphere, which is the uppermost part of the hot, liquid mantle.

Plate Boundaries (pg 112 for pictures)
Plates meet at a plate boundary. These are often sights of eqarthquakes and volcanoes.
3 Types of Plate Boundaries
  1. Divergent- two plates are moving AWAY from each other. The result is new crust material formed at the diverging boundary.
  2. Convergent- two plates moving towards each other. The result is either an upward crunching of the plates, creating mountains, or one plate being pushed under the other. This is called SUBDUCTION.
  3. Transform- two plates sliding past each other.

Famous plate boundaries-
  • The San Andreas Fault between the North American Plate and the Pacific Plate (Transform Fault)
    • Parts of California rests on either side of this plate
    • Mt. St. Helens volcano in Washington is the result of leaking magma at this plate
  • The Himalayas were formed when the India-Australia plate collided with the Eurasian plate (Convergent Boundary)
  • The mid-Atlantic Ridge (Divergent boundary)

How Earthquakes Occur
  • As plates move, they release energy in vibrations and waves called seismic waves
  • The waves begin below ground at the focus of the earthquake (the location of the origination of the waves)
  • The area above ground directly above the focus is called the epicenter. This location experiences the largest seismic movement.
  • Earthquakes can be very small or large. Over 1 million earthquakes occur each year.

Measuring Earthquakes
Seismic activity and waves are measured using a seismograph.
An Earthquake can be quantified two ways
  1. The Richter Scale
    • The Richter Scale was invented by Charles Richter.
    • Each increase of "1" on the Richter scale indicates and increase of 30x magnification in power of the earthquake.
      • For example, an increase of 7 to 8 on the Richter Scale indicates an earthquake 30 times stronger than an earthquake ranked 7, and 900 times stronger than an earthquake ranked 6.
  2. The Moment Magnitude
    • Typically used by Seismologists to measure Earthquakes larger than 6.5
    • Measures the total energy released by the earthquake

Effects of Earthquakes
  • Magnitude 5 earthquakes usually damage property
  • Magnitude 2 earthquakes are generally too small to feel.
  • Approximately every 5 years a magnitude 8 earthquake occurs, causing massive property damage and death.
  • Earthquakes usually have an after-effect result of landslides and tsunamis.

Landslides
The seismic activity causes a break and release rocks, soil, and other debri, which slides swiftly down a mountainside.

Tsunamis
An underwater earthquake, volcanic eruption, or landslide causes an intense wave through ocean water.
This wave can travel through water at more than 750 km/ 450 miles per hour.
Tsunamis may start at about 1 m high in ocean water but reach 30 m high (a 10 story building) as they approach the shallower waters near a shoreline.
Economic and Environmental Effects of Tsunamis
  • Coastal degradation from the impact and current of the wave
  • displaced animals left ashore after the wave leaves
  • Destruction of coastal infrastructure
  • pollution of local coastal area by saltwater
  • Oil and gasoline from overturned vehicles causes water pollution
  • Damage of reefs and offshore coastal environments

Famous Earthquakes/Tsunamis/Fault Areas

1. Pakistan October 8, 2005
  • killed 75,000 people
  • Eurasian and Indian-Australian plate collision

2. Peru 1970
  • resulting landslide killed 17,000 people, buried an entire town

3. South Asian (Indonesia) Tsunami December 26, 2004
  • Indian Ocean earthquake, magnitude 9.4
  • largest earthquake since Alaskan earthquake in 1964
  • more than 240,000 people died
  • tsunami affected South Asia and east coast of Africa

4. San Andreas Fault/California Activity (esp 1906 earthquake)
  • One of the most geologically active areas of the world
  • Pacific plate is moving northward at 3.5 cm/year
  • 1906 8.3 magnitude Earthquake destroyed most of San Fransisco (most damage due to fire caused by ruptured gas lines after the quake)
  • 1989 6.9 magnitude earthquake in Loma Prieta (90 mi south of San Fran) killed 67 people and caused $6 billion in damage

5. Kobe, Japan 1995
  • occurred at smaller faults crisscrossing major plate
  • was difficult to predict because it is a smaller fault and only experiences serious magnitude quakes every 1000-5000 years.