Science 8 - 4th Quarter

• In Period 2, more terms related to earthquakes, how seismic waves are used to study earth's interior, and safety precautions before, during, and after an earthquake will be the focus
• Earthquake


  A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust or volcanic action
• Crust


  • The outermost layer of the earth
  • Mostly made of basalt
  • 6 kilometers (oceanic crust) to 45 kilometers (continental crust) thick

  
• Mohorovicic Discontinuity


  • The boundary between the crust and the mantle
  • 700 km thick

  
• Mantle


  • Takes 84% of the earth's volume
  • Rich in peridotite (igneous rock)
• Gutenberg Discontinuity


  • The boundary between the lower mantle and the upper core
• Core


  • The central part of the earth
  • Rich in sulfur and iron
• Outer core


  • The only liquid layer of the earth
  • 2,550 km thick
  • Believed to be responsible for the magnetic field of the earth

  
• Inner core


  • Solid part of the core
  • 1,220 km thick
  • Lehmann discontinuity - boundary between inner and outer core
• Plate Tectonics Theory


  The earth is divided into several plates that move or slide over the mantle

  
• Most tectonic activity takes place at plate boundaries, where they may collide, tear apart, or slide against each other
• The movement of tectonic plates is made possible by thermal energy (heat) from the mantle part of the lithosphere
• Fault


  • A fracture or crack found between two blocks of rock on Earth's crust along which movement occurs
  • Typically form at the boundaries between Earth's tectonic plates

  
• Fault plane


  • Where the action is; a flat surface that may be vertical or sloping

  
• Fault trace


  • The line the fault plane makes on the Earth's surface

  
• Hanging wall


  • The block usually found above the fault plane

  
• Footwall


  • Usually found under the fault plane
• Active faults


  Those that move one or more times in the last 10,000 years
• Inactive faults


  Those that did not move or have been inactive for millions of years
• Normal Fault


  • The hanging wall moves down relative to the footwall
  • The forces in normal faults are pulling apart
• Reverse Fault


  • The hanging wall moves up relative to the footwall
  • The forces create reverse faults are compressional or pushing toward each other
• Strike-Slip Fault


  • The motion of the blocks is horizontal or sideways
  • Also known as a transcurrent fault
• Focus


  The immediate area where the vibration takes place
• Epicenter


  The surface above the focus