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