Do Now Describe the last earthquake you can remember. (location, strength, time of day, how it felt, etc.) Where do earthquakes occur? Why do earthquakes occur?

Earthquakes / Epicenters Objectives: Define Elastic Limit Identify 3 types of fault lines Differ between P and S waves Determine shadow zones of P and S waves

Where do earthquakes occur? Occur at plate boundaries Convergent: Plates move together Divergent: Plates move apart Transform: Plates are sliding

What Causes Earthquakes When rock reaches its elastic limit an earthquake occurs. Elastic Rebound: the sudden “bounce – back” of rock to its original shape During elastic rebound, rock releases energy. Some of this energy travels as seismic waves that cause earthquakes.

Fault Lines When rock breaks, they move along surfaces called faults. 3 Types of faults Normal Reverse Strike/Slip

Normal fault Force applied = Tensional Movement = Rock above fault moves downward. Before After What plate boundary is a normal fault similar to? Divergent

Normal Fault Hanging wall slides below the foot wall.

Reverse Fault Force applied = Compressional Movement = Rock above fault moves Upward. Before After What boundary is a reverse fault similar to? Convergent

Reverse Fault Hanging wall slide up passed the foot wall Hanging Wall

Strike/Slip fault Force applied = Shearing Movement = Rocks slide past each other. Energy builds up until elastic limit is reached = Earthquake Before After What boundary is a strike/slip fault similar to? Transform

Strike/Slip Fault Strike/Slip fault show how the fault line will cause the 2 sides to not line up.

Do Now Define Elastic Limit List and describe the 3 types of fault lines State which applied force creates each type of fault

SEISMIC WAVES When earthquakes occur, waves of energy SEISMIC WAVES travel outward from the earthquake focus 3 types of seismic waves are produced AT THE SAME TIME but each behaves differently within earth.

P (Primary) Waves Primary waves or compression waves vibrate parallel to the direction of movement. (slinky) Travel faster than any other wave (6-8 km/s) Travel through solids, liquids, and gases

S (Shear) WAVE Shear wave or secondary waves vibrate back and forth perpendicular to the direction the wave is moving Slower than P waves (4-5 km/s) TRAVEL THROUGH SOLIDS ONLY

SURFACE OR LONG WAVES Vibrations travel along earth’s surface in a circular motion at relatively slow speeds (2 km/s) like waves in a pond Do more damage because they produce more ground movement

Velocity and seismic waves Velocity depends on the material they are passing through Increase density and pressure – greater the velocity Waves are refracted or bent as waves pass through material with different densities

Shadow Zone An area where earthquake waves seem to disappear. P-Waves can travel through solid, liquid, and gas. S-waves can travel through SOLID ONLY! P-Waves enter liquid outer core = Wave slows down! S-Waves enter liquid core = Waves disappear.

Shadow Zone S-Waves do not make it through. Cant travel through liquid outer core.

P Wave and S Wave Chart / Locating Epicenters Objectives: Analyze P and S wave chart Determine travel times of seismic Waves Analyze seismograms Locate epicenters

Determining distance to Epicenter Epicenter – The location of an earthquake on the surface of the Earth above the focus. Focus – Location within the Earth’s crust where the breaking of rock occurs Surface

Seismograph / Seismogram Geologist use an instrument to measure seismic waves called a seismograph. Measures the arrival times of the P-Wave, S-Wave, and Surface Wave. Which wave will always arrive first??? P (Primary) Wave = Faster Speed

P – S Wave Chart Chart can be used to determine arrival times of P and S waves. Can also be used to locate the distance to the epicenter from the seismic station.

This represents TIME (in minutes!) Notice the vertical axis This represents TIME (in minutes!) Let’s enlarge a small section

20 Between each minute, we notice that there are 3 segments. If there are 60 seconds in a minute, each one of these segments must be ________seconds. 20

What would this time be? 2 minutes, 20 seconds

This represents DISTANCE (in thousands of Kilometers!) Notice the horizontal axis This represents DISTANCE (in thousands of Kilometers!) Let’s enlarge a small section

So what would this distance be? 1,000km 2,000km 1,200km 1,400km 1,600km 1,800km So what would this distance be? Fill these in... 5,400km

There are also two curves on this chart that display the way different earthquake waves behave.

S-Wave P-Wave

This chart can be used for answering many different questions! Let's try a few examples How long does it take an S-Wave to travel 5,000km? Go to the chart!

Another example... Go to the chart! The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them. How far away from the epicenter of the earthquake must they be? Go to the chart!

3,600km

Another example... Go to the chart! I know that there was a 7 minute difference in the arrival of my P and S waves. How far away from the epicenter must I be? Go to the chart!

Slide your scrap paper up until the tick marks match up with the curves… Mark off 7 minutes on scrap paper…

LOCATING THE EPICENTER OF AN EARTHQUAKE The difference in travel time between P and S waves can be used to determine the DISTANCE from a station to the epicenter The farther the station , The longer the travel time. TO DETERMINE THE EXACT LOCATION OF AN EPICENTER, you must have 3 seismic stations recording the same earthquake

Locating an Epicenter Station A Station C Epicenter Station B

Collecting data from the recording stations: Station A: San Francisco, California P-Wave arrival 3:02:20 S-Wave arrival 3:06:30 4:10

Collecting data from the recording stations: Station B: Denver, Colorado P-Wave arrival 3:01:40 S-Wave arrival 3:05:00 What is the time difference between P and S wave arrivals? 3:20

Collecting data from the recording stations: Station C: Missoula, Montana P-Wave arrival 3:01:00 S-Wave arrival 3:03:00 What is the time difference between P and S wave arrivals? 2:00

Find the distance to the epicenter for each station. Using the P and S wave chart, Find the distance from each station to the epicenter. San Francisco: 4:10 2,800km Denver, Colorado: 3:20 2,200km Missoula, Montana 2:00 1100km

Recording Board Difference in arrival times: San Francisco: 41:0 2,800km Open your compass to the EXACT distance on the scale. 1,000 2,000 3,000 4,000 5,000

. . . Use your carefully set compass to draw a circle around each seismic station. . . .

How are earthquakes measured? Seismographs measure an earthquakes Magnitude – The amount of energy released. The Richter Scale measure local intensity. Describes how much energy is released.

Tsunamis Tsunamis – Ocean waves caused by seismic waves.