Dynamic Crust:Dynamic Crust:EarthquakesEarthquakes

Final Exam ReviewFinal Exam Review

Focus— point beneath the Focus— point beneath the Earth’s surface where fault Earth’s surface where fault movement releases seismic movement releases seismic waves.waves.

Epicenter— the point on Epicenter— the point on Earth’s surface directly above Earth’s surface directly above the focus.the focus.

P-Waves (Compressional)P-Waves (Compressional)--primary (comes first)--primary (comes first)

--travels through solid,--travels through solid,

liquid and gasliquid and gas

--fast (arrives first at station)--fast (arrives first at station)

Liquid—outer core

S-Waves (shear)S-Waves (shear)--secondary (comes 2--secondary (comes 2ndnd))

--travels through solid--travels through solid

onlyonly

--slow (arrives at station second)--slow (arrives at station second)

Cannot travel through liquid!!

LOCATING THE LOCATING THE EPICENTEREPICENTER

1.1. Need at least 3 stationsNeed at least 3 stations2.2. Determine when the P wave arrivesDetermine when the P wave arrives3.3. Determine when the S wave arrivesDetermine when the S wave arrives4.4. Difference between S and P wave Difference between S and P wave

arrivalarrival5. Locate on travel-time curve the 5. Locate on travel-time curve the difference in S and P wave arrival times difference in S and P wave arrival times in correspondence to distance (x-axis)in correspondence to distance (x-axis)6. Draw circles around each station6. Draw circles around each stationwith distance determined in step 5with distance determined in step 57. Intersection of the three circles is the epicenter7. Intersection of the three circles is the epicenter

1. 1. Approximately Approximately how long does how long does an earthquake an earthquake P-wave take to P-wave take to travel the first travel the first 6500 kilometers 6500 kilometers after the after the earthquake earthquake occur? occur?

10 minutes

2. Compared to the thickness and 2. Compared to the thickness and density of the continental crust of density of the continental crust of South America, the oceanic crust of South America, the oceanic crust of the Pacific floor is…the Pacific floor is…

a. thinner and less densea. thinner and less dense

b. thinner and more denseb. thinner and more dense

c. thicker and less densec. thicker and less dense

d. thicker and more densed. thicker and more dense

3. A 3. A seismograph seismograph station station records a records a difference in difference in arrival time arrival time between the between the S- and P-wave S- and P-wave of 4 minutes. of 4 minutes. About how far About how far away is the away is the earthquake earthquake epicenter? epicenter?

2,600 km

4. A P-wave 4. A P-wave arrives at a arrives at a station located in station located in Seattle, Seattle, Washington at Washington at 2:35:20. An S-2:35:20. An S-wave arrives at wave arrives at 2:37:10. What is 2:37:10. What is the distance to the distance to the epicenter of the epicenter of the earthquake?the earthquake?

2:37:10 -2:35:20 1:50

1000 km

5. A P-5. A P-wave wave arrived at a arrived at a station 4 station 4 minutes minutes and 40 and 40 seconds seconds before the before the S-wave. S-wave. What is the What is the distance to distance to the the epicenter epicenter of the of the earthquakeearthquake??3,200 km

6. The arrival of 6. The arrival of P-waves and S-P-waves and S-waves at a waves at a seismic station seismic station indicated that indicated that an earthquake an earthquake occurred 4,000 occurred 4,000 kilometers from kilometers from the station. The the station. The P-wave arrived P-wave arrived at 3:32:30 p.m. at 3:32:30 p.m. When did the When did the earthquake earthquake occur?occur?

1. How long does ittake a P-Wave totravel 4,000 km?

7 minutes

2. 3:32:30 7:003:25:30 pm

7. A seismic 7. A seismic station receives station receives a P-wave at a P-wave at 12:07 a.m. and 12:07 a.m. and an S-wave at an S-wave at 12:12 a.m. 12:12 a.m. What is the What is the station’s station’s approximate approximate distance from distance from the epicenter?the epicenter?

1. What is thedifference betweenarrival times?

12:12 am12:07 5 minutes

2. Measure and Match

3,500 km

8. At which station is the difference in 8. At which station is the difference in time between the arrival of P- and S-time between the arrival of P- and S-

waves the greatest? waves the greatest?

D. P-waves travel faster so they will arrive first. S-waves would never make it to stations E and F.

9. What explanation do scientists give for 9. What explanation do scientists give for the reason that station F did not receive the reason that station F did not receive

S-waves? S-waves?

2.The Earth's outercore is liquid, whichdoes not allow S-wavesto pass.

10. Seismograph 10. Seismograph station D is 7,700 station D is 7,700 kilometers from kilometers from the epicenter. If the epicenter. If the P-wave the P-wave arrived at this arrived at this station at 2:15 station at 2:15 p.m., at p.m., at approximately approximately what time did the what time did the earthquake earthquake occur? occur? 1. How long does it

take an earthquakeP-wave to travel 7,700 km?

11 minutes

2. 2:15:00 pm 11:00 min2:04:00

11. Seismograph 11. Seismograph station B recorded station B recorded the arrival of P-the arrival of P-waves at 2:10 p.m. waves at 2:10 p.m. and the arrival of and the arrival of S-waves at 2:15 S-waves at 2:15 p.m. p.m. Approximately how Approximately how far is station B far is station B from the from the earthquake earthquake epicenter? epicenter?

1. What is the difference betweenarrival times?

2:15 - 2:10

5 minutes

2. Measure andMatch

3,400 km