Earthquake Let’s shake, rattle and roll

Earthquake Basics Earthquake – shaking of Earth’s crust caused by the sudden release of energy Energy build over time until stresses break the rocks Happen ~ every 30 seconds ~3,000 annually strong enough to move sections of Earth’s crust ~20 annually cause severe damage Can only occur in the rigid crust!

World Seismicity

U.S. Seismicity

Seismic Activity in the West

Causes Elastic Rebound Theory – 1.Pressure and stress begin to build along plate or fault boundaries 2.Pressure causes deformation and shape changes in rock 3.Stress becomes great enough to overcome friction 4.Plate or fault suddenly move 5.Plate or fault snap back to previous shape

Elastic Rebound Theory

Elastic Rebound Theory Real Life

Earthquake Definitions The point on the fault plane at which the first movement of the earthquake occurs The point on the earth’s surface directly above the focus of the earthquake A break or crack in the earth’s crust from which movement occurs. Focus or Hypocenter Epicenter Fault

Seismic Waves Travel & act much like sound waves 2 basic types Body Waves (2 types) –Compressional, Primary or P wave –Shear, Secondary or S wave Surface waves (2 types) Product of P & S waves reaching the surface –Love or L Waves –Rayleigh waves

P Waves Fastest traveler 1 st to be recorded Travel through all materials (rock, fluids, air) Move straight along ground in an accordion fashion like a spring or slinky

S Wave 2 nd fastest wave Travels ~1/2 speed of P wave Particles move at right angles to the direction of travel Only move in solids Cannot move in fluids or air

Love Waves Slower than both P & S waves Travel like ripples in a pond Very destructive!!!

Time Travel Graph A time travel graph is used to find the distance to the epicenter.

Do Earth quake lab #1 Finding the distance to the epicenter.

Locating an Earthquake The Basics of Seismic Exploration

1. seismograph- instrument used to measure Earth’s movements. 2. The pattern of seismic waves produced by a seismograph = seismogram 3. Richter Scale- measures earthquake’s magnitude (size of earthquake/amount of seismic waves)

Missoula Denver San Francisco

Guide to reading a seismogram

Use the data from the recording stations:  Station A: San Francisco, California P-Wave arrival 3:02:20S-Wave arrival 3:06:30 What is the time difference between P and S wave arrivals?

Use the data from the recording stations:  Station B: Denver, Colorado P-Wave arrival 3:01:40S-Wave arrival 3:05:00 What is the time difference between P and S wave arrivals?

Use the data from the recording stations:  Station C: Missoula, Montana P-Wave arrival 3:01:00S-Wave arrival 3:03:00 What is the time difference between P and S wave arrivals?

Difference in arrival times: San Francisco: 4:10 Denver, Colorado: 3:20 Missoula, Montana: 2:00

MOVE THE PAPER UNTIL THE TWO TICK MARKS LINE UP WITH THE P AND S CURVES WHEN TICK MARKS LINE UP, GO STRAIGHT DOWN AND READ THE EPICENTER DISTANCE EPICENTER DISTANCE OF 2800 KM

Recording Board Difference in arrival times: San Francisco: 4:10 =2,800km 1,000 2,000 3,000 4,0005,000 Open your compass to the EXACT distance on the scale.

EPICENTER DISTANCES San Francisco: 4:10 Denver, Colorado: 3:20 Missoula, Montana 2:00 2,800km 1,100km 2,000km

... 2,800km 2,000km 1,100km Triangulation

How are the Size and Strength of an Earthquake Measured? Magnitude –Richter scale measures total amount of energy released by an earthquake; independent of intensity –Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale

Site #1 Dist = 300km Amp = 50mm Site #2 Dist = 600km Amp = 5mm Site #3 Dist =100km Amp = 500mm

Hand out Lab packet.. :O)