1. GEOL 108 - Crises of a Planet Lab 2 - Locating Earthquakes Sept. 9 - 14, 2012 Department of Earth Sciences

2. EARTHQUAKES | 2 LAB 2 - EARTHQUAKES - KEY CONCEPTS Reading seismograms Using travel time curves to triangulate an epicenter Predicting tsunami arrivals

3. Department of Earth Sciences EARTHQUAKES | 3 SEISMIC WAVES Release of accumulated energy leads to quake Energy travels in waves of vibration −Body waves P-waves - primary S-waves - secondary −Surface waves Love Rayleigh Waves travel at different known velocities

4. Department of Earth Sciences EARTHQUAKES | 4 DETERMINING QUAKE EPICENTER Step 1: Identify P and S arrival times 2:37:10 2:41:50

5. Department of Earth Sciences EARTHQUAKES | 5 DETERMINING QUAKE EPICENTER Step 2: Subtract arrival times to get S-P delay 2:37:10 2:41:50 S-P delay = 2:41:50 – 2:37:10 S=P delay = 0:04:40 (4 minutes, 40 seconds)

6. Department of Earth Sciences EARTHQUAKES | 6 DETERMINING QUAKE EPICENTER Step 3: Use seismic wave travel time vs. distance chart to determine distance to epicenter Find where S-wave line minus P-wave line equals the delay you determined S-P delay = 2:41:50 – 2:37:10 S-P delay = 0:04:40 (4 minutes, 40 seconds) Read what distance that delay corresponds to… ~ 3,600 km here

7. Department of Earth Sciences EARTHQUAKES | 7 DETERMINING QUAKE EPICENTER Repeat steps 1-3 for two other seismic stations Distance to epicenter (determined from reading seismographs, not shown) Los Angeles: 1800 km Austin: 3150 km Urbana: 3400 km

8. Department of Earth Sciences EARTHQUAKES | 8 DETERMINING QUAKE EPICENTER Step 4: Use a compass to plot all possible epicenter locations. The epicenter is where they intersect. Distance to epicenter (determined from reading seismographs, not shown) Los Angeles: 1800 km Austin: 3150 km Urbana: 3400 km

9. Department of Earth Sciences EARTHQUAKES | 9 TSUNAMIS http://www.youtube.com/watch?v=2uJN3Z1ryck Fukushima Prefecture, Japan. Photograph by Sadatsugu Tomisawa, AP

10. Department of Earth Sciences EARTHQUAKES | 10 PREDICTING TSUNAMI ARRIVALS Tsunamis are triggered by earthquakes Tsunamis travel at 600 km/hr on average Given a known epicenter, you can predict the tsunami arrivals elsewhere by rearranging the equation we used last week (velocity = distance / time) Assignment will ask you to plot how far a tsunami has traveled in 1, 2, 3 and 4 hours. So what should you solve the above equation for?