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While on the flank of Mammoth Mountain with Bill Ellsworth one day during the 1989 Mammoth Mountain earthquake swarm, we both heard muffled booming sounds but felt no shaking. On checking, we found that the earthquakes during that period were shallow (< 4 km deep) with magnitudes M < 2.0. This may explain reports by people living on the flanks of restless volcanoes of ominous booming sounds that both feed local legends and serve as an early warning of a possible impending eruption.
Dave Hill is a research geophysicist with the U.S. Geological Survey in Menlo Park, CA. He has served as Scientist-in-Charge of the Long Valley Observatory from 1982 to April 2009, Chief of the Seismology Branch from 1978-1982, and as Staff Seismologist at the Hawaiian Volcano Observatory from 1964-1966.
Much of my research has focused on processes driving unrest in large, silicic calderas with particular emphasis on Long Valley Caldera in eastern California. My approach is that of a seismologist interested in regional tectonic-magmatic interactions, seismotectonics, crustal structure, earthquake source mechanisms, and seismic wave propagation. A closely related interest involves an effort to understand remote triggering of seismicity (including “non-volcanic” tremor) and volcanic unrest by dynamic stresses in the form of seismic waves from large, distant earthquakes. Remote triggering is a promissing tool for probing the physical state of crustal volumes that have reached some form of criticality.
Originally posted by PuterMan
reply to post by summer5
I think first of all any noise that goes on as long as 20 minutes is probably not an earthquake. An earthquake lasts but a few seconds or in extreme case a minute or two. They certainly never last 20 minutes.
I am not saying these are not earthquake related, just that what you are hearing is not the P wave of a quake, or related to the P wave.
In many many ways I wish I could hear this sound. i don't mean on a recording, I mean to be in it to feel it around me. I am very susceptible to low frequency sound and I am sure If I could hear/feel it I could get an idea of what it may be.
The plains are gravel, if that makes a difference to the way sound is generated etc.
The rumble we hear (it's very very distinguishable from any other potential noise, sounds like nothing on earth) is very very low resonance, you can almost 'feel' it as well as hear it. It is eerie. It's strange because it's so low you feel you ought not to be able to hear it, yet it's very audible (if that makes sense) yet it's not LOUD... but all around you.
The LOUD noises, more like jets, arrive with the movement. Particularly the 7.1 (about 12km from me) which when it hit sounded like several large jumbo jets landing in the garden, and continued for a good 40 secs with the movement.
Sometimes booming will be heard with NO movement. This type of boom is different - short and sharp like an explosion. I've experienced this too, as have many I know. These are weird ones because you brace yourself but nothing comes. I've noticed these are often v. shallow and close by and small quakes (sub 2.5). This was the case the day before the 7.1 where residents near the epicentre (which is also fairly need a small Army shooting/bomb practice range) had rung the Police after hearing booming to check it was the range. It wasn't. Next day the 7.1 hit.
The propagation velocity of the waves depends on density and elasticity of the medium. Velocity tends to increase with depth, and ranges from approximately 2 to 8 km/s in the Earth's crust up to 13 km/s in the deep mantle.