GEOL 108 - Crises of a Planet
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GEOL 108 - Crises of a Planet Lab 2 - Locating Earthquakes . Sept. 9 - 14, 2012. Department of Earth Sciences. LAB 2 - EARTHQUAKES - KEY CONCEPTS Reading seismograms Using travel time curves to triangulate an epicenter Predicting tsunami arrivals. EARTHQUAKES | 2.

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GEOL 108 - Crises of a Planet Lab 2 - Locating Earthquakes

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Geol 108 crises of a planet lab 2 locating earthquakes

GEOL 108 - Crises of a PlanetLab 2 - Locating Earthquakes

  • Sept. 9 - 14, 2012

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • LAB 2 - EARTHQUAKES - KEY CONCEPTS

  • Reading seismograms

  • Using travel time curves to triangulate an epicenter

  • Predicting tsunami arrivals

EARTHQUAKES | 2

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • 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

EARTHQUAKES | 3

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • DETERMINING QUAKE EPICENTER

  • Step 1: Identify P and S arrival times

2:37:10

2:41:50

EARTHQUAKES | 4

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • DETERMINING QUAKE EPICENTER

  • Step 2: Subtract arrival times to get S-P delay

S-P delay = 2:41:50 – 2:37:10

S=P delay = 0:04:40

(4 minutes, 40 seconds)

2:37:10

2:41:50

EARTHQUAKES | 5

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • DETERMINING QUAKE EPICENTER

  • Step 3: Use seismic wave travel time vs. distance chart to determine distance to epicenter

S-P delay = 2:41:50 – 2:37:10

S-P delay = 0:04:40

(4 minutes, 40 seconds)

Find where S-wave line minus P-wave line equals the delay you determined

Read what distance that delay corresponds to…

~ 3,600 km here

EARTHQUAKES | 6

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • 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

EARTHQUAKES | 7

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • 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

EARTHQUAKES | 8

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • TSUNAMIS

  • http://www.youtube.com/watch?v=2uJN3Z1ryck

Fukushima Prefecture, Japan. Photograph by SadatsuguTomisawa, AP

EARTHQUAKES | 9

Department of Earth Sciences


Geol 108 crises of a planet lab 2 locating earthquakes

  • 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?

EARTHQUAKES | 10

Department of Earth Sciences


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