planet earth earthquakes - study involves waves, forces, solids, liquids, and heat. and leads to an...
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Planet Earth
• Earthquakes - study involves waves, forces, solids, liquids, and heat. And leads to an understanding of the structure of the earth.
Earthquakes
• Detection
• Cause
• Strength
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 Newton’s 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.
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
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.
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
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