Earthquakes

Warm-up What other damaging effects can be caused by earthquakes other than the earthquake itself?

Earthquakes Mostly caused by plate tectonics Two plates moving in different directions (usually transverse) Rock has a lot of friction, so they don’t slide easily Stress builds over time (energy storage) Stress is the force acting on a rock over a certain area When stress overcomes the strength of the rock, movement occurs The vibrations from this are felt as an earthquake (energy release)

Stress Three kinds: Compression Tension Shear

Faults Fracture in the crust along which the earth moves 3 kinds

Reverse fault

Normal Fault

Strike-Slip Fault

Anatomy of an earthquake Focus: Where the actual earthquake occurred Epicenter: The point on the surface directly above the focus

Seismic waves 3 types, all move differently Body waves: Surface waves Primary Secondary Surface waves

Primary waves P-waves Push-pull of rock First to arrive Pass through the interior of the Earth Can pass through solid rock and liquids (water and molten rock) Body waves

Secondary Waves S-waves Second to arrive Pass through the interior of the Earth Only can pass through solids Body waves

Surface Waves Last to arrive to arrive Travel through the surface only Cause the most damage

Seismometer Instruments that measure motion of the ground Hanging mass (pendulum) stays still while the Earth moves under it The paper moves and the mass drags a marker across the paper The bigger the squiggle, the more energy released Records a seismogram, the graph showing the movement

Seismogram

Measuring Damage 3 scales: The Richter magnitude scale The Modified Mercalli Intensity Scale The moment magnitude scale

The Richter magnitude scale assigns a magnitude number to quantify the size of an earthquake measured with a seismometer Measures how powerful it was Logarithmic scale (meaning each # is 10x worse so a 3 is 10x stronger than a 2 and 100x stronger than a 1)

The Modified Mercalli Intensity Scale The effect of an earthquake on the Earth's surface is called the intensity  refers to the effects actually experienced at that place (damage assessment) Non-scientific, but relevant Very inaccurate judgement of the earthquake itself

The moment magnitude scale Most precise Measures actual energy released Based on the area of the fault that moved at the same moment as an earthquake