Plate Tectonics: Earthquake Generation and Wave Behavior Do Now: Explain why New York State is not prone to high earthquake activity. Use the map of the Earth’s tectonic plates to justify your answer

What causes an earthquake? Elastic Rebound Video Link 1.) As rigid plates collide, diverge, or scrape past one another, stress builds in the crust 2.) Eventually the rock can no longer bend under such high stress, and breaks or “slips” along a fault 3.) The shock of this slip within in the crust releases energy in the form of seismic waves

EVIDENCE OF CRUSTAL MOVEMENT: FAULTS EVIDENCE OF CRUSTAL MOVEMENT: FAULTS! (BREAKS IN EARTHS CRUST SHOWING DISPLACEMENT)

Focus Animation Focus- The point of slip/rupture along a fault. Seismic waves radiate outwards from this point Epicenter- The point on the earth’s surface directly above the focus

Seismic Waves 1.) P-waves (Primary)- Arrive first and are compression or “push/pull” waves. They travel the fastest and through all mediums (solids and liquids) 2.) S-waves (Secondary)- Arrive second and are transverse, moving side to side like a wave in a rope and only through solid layers 3.) L-Waves- surface waves that occur once P & S wave have both arrived. MOST damaging

P waves will travel through all layers of the earth, but refract when entering different substances. The bending of P-waves when they reach the core causes a P-Wave Shadow Zone. S-Waves will not travel through the outer core at all causing a larger S-Wave shadow zone

As distance from the epicenter increases, the travel time for P and S waves ______. As the distance from the epicenter increases, the lag time between P and S waves (S-P) also _______.

Seismographs seismic waves are detected with a sensitive instrument called a seismograph A seismogram shows the arrival times and strength of seismic waves

#1The higher the amplitude (wave height) on the seismogram—the stronger the earthquake is.

Finding The Distance to the Epicenter How does one find the distance to an epicenter? Click here for animation ESRT Interactive Chart

Origin Time= P arrival time - P travel time Origin time is the actual time that the Earthquake occurred at the epicenter To solve origin time you must know: 1.) What time the P waves first arrived at any station 2.) The travel time (how long it took P-Waves to get there) using the distance from the epicenter on the x-axis

In Perspective: A friend of yours who lives a half an hour away arrives at your house at 10:45 a.m. Based on this, you know they must have left at 10:15 a.m. Real example: An Earthquake was recorded at station A at 2:25:00 p.m. You have the following information: The epicenter is 4000(km) away Step 1: What is the travel time of the P-waves? ________ Step 2: Based on the travel time, what is the origin time of the Earthquake? ______________

Locating an Earthquake Epicenter on a Map (AKA Triangulation) Triangulation You need a minimum of THREE (3) seismic stations to do this 1.) Calculate difference in P and S wave arrival times 2.) Use same method to find Epicenter Distance 3.) Draw circle around the seismic station with a radius equal to the distance to the epicenter.

Where the 3 circles intersect denotes the location of the Epicenter

Step 1: Using the map and a scrap sheet of paper, mark off the distance to the epicenter for each of your first seismic station (here San Francisco)

Step 2: Mark that distance from the location of the seismic station on your map.

Step 3: Place the center of your compass (metal ring) directly over the seismic station location, then place your pencil in at the distance that most aligns with the mark you made on your map. Hold compass firmly and draw your circle! Do this for all 3 stations

Step 4: Mark the epicenter with an “x” where are 3 stations intersect

Mercalli measures impact on humans from shaking

Richter measures actual amplitude of seismic waves and ↑ 10x every number on the scale (1-10)

Damage by Earthquakes Subsidence- sinking land Landslides Demolished Buildings and Roads Liquifaction- sediments + ground water become fluid AND TSUNAMIS…..

Tsunami: 700-800 km/hr & up to 20 (m) in height Tsunami: 700-800 km/hr & up to 20 (m) in height! Tsunami Generation Animation Link 1.) Earthquake occurs under the ocean 2.) Displaced crust “shoves” water upward , creating a massive wave

Right before a Tsunami hits the water recedes Japan

Do Now: Where would you expect Shallow Focus vs Do Now: Where would you expect Shallow Focus vs. Deep Focus Earthquakes to occur along plate boundaries? Where and WHAT types of boundaries?

Map: Chili earthquake foci depths: Depth increases as submergence depth increases Green: 0-80 km Yellow: 81-290 km Red: 291-667