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
Department of Earth Sciences
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
DETERMINING QUAKE EPICENTER
• Step 1: Identify P and S arrival times
2:37:10
2:41:50
EARTHQUAKES | 4
Department of Earth Sciences
DETERMINING QUAKE EPICENTER
• Step 2: Subtract arrival times to get S-P delay
2:37:10
S-P delay = 2:41:50 – 2:37:10
S=P delay = 0:04:40
(4 minutes, 40 seconds)
2:41:50
EARTHQUAKES | 5
Department of Earth Sciences
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
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
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
TSUNAMIS
Fukushima Prefecture, Japan. Photograph by Sadatsugu Tomisawa, AP
• http://www.youtube.com/watch?v=2uJN3Z1ryck
EARTHQUAKES | 9
Department of Earth Sciences
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