2 Focus— point beneath the Earth’s surface where fault movement releases seismic waves.
3 Epicenter— the point on Earth’s surface directly above the focus.
4 P-Waves (Compressional) --primary (comes first)--travels through solid,liquid and gas--fast (arrives first at station)Liquid—outer core
5 S-Waves (shear) --secondary (comes 2nd) --travels through solid only --slow (arrives at station second)Cannot travel through liquid!!
6 LOCATING THE EPICENTER Need at least 3 stationsDetermine when the P wave arrivesDetermine when the S wave arrivesDifference between S and P wavearrival5. Locate on travel-time curve thedifference in S and P wave arrival timesin correspondence to distance (x-axis)6. Draw circles around each stationwith distance determined in step 57. Intersection of the three circles is the epicenter
7 1. Approximately how long does an earthquake P-wave take to travel the first 6500 kilometers after the earthquake occur?10 minutes
8 2. Compared to the thickness and density of the continental crust of South America, the oceanic crust of the Pacific floor is…a. thinner and less denseb. thinner and more densec. thicker and less densed. thicker and more dense
9 3. A seismograph station records a difference in arrival time between the S- and P-wave of 4 minutes. About how far away is the earthquake epicenter?2,600 km
10 4. A P-wave arrives at a station located in Seattle, Washington at 2:35:20. An S-wave arrives at 2:37:10. What is the distance to the epicenter of the earthquake?2:37:10-2:35:201:501000 km
11 5. A P-wave arrived at a station 4 minutes and 40 seconds before the S-wave. What is the distance to the epicenter of the earthquake?3,200 km
12 6. The arrival of P-waves and S-waves at a seismic station indicated that an earthquake occurred 4,000 kilometers from the station. The P-wave arrived at 3:32:30 p.m. When did the earthquake occur?How long does ittake a P-Wave totravel 4,000 km?7 minutes3:32:307:003:25:30 pm
13 7. A seismic station receives a P-wave at 12:07 a. m 7. A seismic station receives a P-wave at 12:07 a.m. and an S-wave at 12:12 a.m. What is the station’s approximate distance from the epicenter?What is thedifference betweenarrival times?12:12 am12:075 minutesMeasure and Match3,500 km
14 8. At which station is the difference in time between the arrival of P- and S-waves the greatest? D. P-waves travel faster so they will arrive first. S-waves would never make it to stations E and F.
15 9. What explanation do scientists give for the reason that station F did not receive S-waves? The Earth's outercore is liquid, whichdoes not allow S-wavesto pass.
16 10. Seismograph station D is 7,700 kilometers from the epicenter 10. Seismograph station D is 7,700 kilometers from the epicenter. If the P-wave arrived at this station at 2:15 p.m., at approximately what time did the earthquake occur?How long does ittake an earthquakeP-wave to travel7,700 km?11 minutes2:15:00 pm11:00 min2:04:00
17 11. Seismograph station B recorded the arrival of P-waves at 2:10 p. m 11. Seismograph station B recorded the arrival of P-waves at 2:10 p.m. and the arrival of S-waves at 2:15 p.m. Approximately how far is station B from the earthquake epicenter?What is thedifference betweenarrival times?2:15- 2:105 minutesMeasure andMatch3,400 km