Planet Earth

1
Planet Earth

• Earthquakes - study involves waves, forces,
  solids, liquids, and heat. And leads to an
  understanding of the structure of the earth.

2
Earthquakes

• Detection
• Cause
• Strength

3
Detection

• Seismograph
• Simple device that detects the s and p waves.
  The time delay in the arrival of these waves
  gives the distance to the quake.
• It uses Newtons first law - the definition of
  inertia. A simple devise that reacts to
  shaking
• 3 seismographs at different locations are needed
  to find the focus of the quake.

4
Cause

• Plates sliding against each other exceeding the
  elastic limit of the rock.
• divergent - move away - Mid-Atlantic rift
• convergent - move toward
• subduction - trenches - Mariana Trench
• collision - mountains - Sargos Mts. in Iran
• transform - slide past each other - Southern CA

5
Strength

• Rock rigidity - force needed to break rock
• Slip distance - distance plates move
• fault area - area of contact
• M0 rigidity x slip distance x fault area
• M0 is defined to be proportional to the
  amplitude of the signal on the seismograph and is
  known as the moment.

6
Strength II

• The moment, M0 is a measure of the intrinsic
  strength of the quake. The range of strengths
  varies greatly.
• M log M0
• M M0
• 1 10 Richter scale quotes M
• 2 100
• 4 10000