Acoustic gravity waves
Many of those mysterious sounds of groans and hums heard around the world are acoustic gravity waves — waves in the deep. An acoustic gravity wave is a special type of sound wave that can cut through the deep ocean at the speed of sound. They can be generated by underwater earthquakes, explosions, and landslides, as well as by surface waves and meteorites. They often precede a tsunami or rogue wave.
Usama Kadri, a researcher at MITs Department of Mechanical Engineering says “Since acoustic-gravity waves are so much faster than tsunamis or rogue waves, successful recordings of acoustic-gravity waves would enhance current tsunami warning systems dramatically, improving detection by minutes to hours depending on the source location. . .” (Kadri published his results in the Journal of Geophysical Research: Oceans.)
*___Acoustic Gravity Waves – (infrasound, low-frequency [20-100 Hz] modulated by ultra-low infrasonic waves [0.1-15 Hz]).
Earth Changes Hotline by Barbara Schneider 
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