<p>Activities for Episode Five, Over the Edge Activity 5.1: Acoustic Monitoring of Undersea Earthquakes</p><p>What is Hydroacoustics? Go to NOAA’s Sounds in the Sea web site and read their mission plan: http://oceanexplorer.noaa.gov/explorations/sound01/background/plan/plan.h tml</p><p>Then complete the following:</p><p>1. Define hydroacoustics (underwater acoustics). 2. List five physical and three biological sources of sound in the ocean. 3. List five man-made sources of sound in the ocean. 4. What is SOSUS and how was it used historically? How is it used now? 5. What is NOAA’s Sound in the Sea project and what scientific goals does it hope to achieve?</p><p>Listen to the Sea Now that you’re familiar with the project, let’s hear some of their results. Listen to the Astoria Canyon earthquake sound first: http://oceanexplorer.noaa.gov/explorations/lewis_clark01/background/hydro acoustics/media/sup3_earthquake_sound.html</p><p>Watch the spectrogram while you are listening to the sound. Listen a couple times to get a feel for how the sound and the spectrogram match up.</p><p>Now try a volcanic tremor: http://oceanexplorer.noaa.gov/explorations/sound01/background/seasounds/ media/tremorx16.html</p><p>Again, keep an eye on the spectrogram to get a feel for how it matches with the sound.</p><p>Now listen to these sounds in “The Sound in Sea Gallery” and look at the spectograms: The NOAA ship Ronald H. Brown Airguns Northeast Pacific blue whale</p><p>Interpreting Spectrograms Now surf on over to the Vents Program site where recent monitoring data are available. View the spectrogram and listen to the acoustic signal of the April 2001 Gorda Ridge eruption: http://pmel.noaa.gov/vents/acoustics/seismicity/nepac/gorda2001/onset.htm l</p><p>You will also want to read this page:</p><p> http://pmel.noaa.gov/vents/acoustics/seismicity/nepac/gordaridge01.html</p><p>Complete the following: 1. Where is the Gorda Ridge and why do eruptions occur there? 2. What is the difference between the axes of the spectrogram of the Astoria Canyon earthquake and the spectrogram of the Gorda Ridge eruption? 3. Describe how colors are used to indicate the frequency of sound. 4. How do the colors of the spectrogram “sound”? Describe the colors and “shape” of loud sounds versus background noise. 5. What were the results of the “response” cruise following this event?</p><p>Can You Identify These Sounds? The NOAA site also has a collection of mystery sounds. Go to this page: http://pmel.noaa.gov/vents/acoustics/sounds_mystery.html</p><p>Listen to one or more of the mystery sounds listed (i.e. Bloop, Julia, Slowdown, etc.)</p><p>Using the audio and the spectrograms as your evidence, argue for whether you think the sound is seismic, biological, or man-made. Include in your argument a comparison with known sounds from each of these types.</p>