Just a couple of quick questions that came up in a conversation I was having with my wife:
If one is, say, out in the middle of the desert with no man-made structures around as an earthquake approaches, can one hear a rumble as it approaches?
If one is airborne above a major fault line as an earthquake erupts and the fault line breaks, could a pressure wave be felt?
Does there exist any kind of aerial video footage of an earthquake as it happens? If not, what would it look like?
Not quite what you’re asking, but when I was 10 or so, we had a mild earthquake in New Hampshire that we heard approach quite clearly (it sounded like a very low-flying airliner), despite living in an extremely sparsely populated forest area.
Oddly, my mother, having gone out to get the mail, noticed nothing.
I’m not sure how one would ever hear an earthquavke before one felt it. Sound travels (IIRC) 13 1/2 to almost 16 times faster through solids than through air, so it would seem that it would be impossible to “hear” it first. (I may be misremembering the details or misunderstanding the question, so I am open to correction, but I recall air as being the slowest medium through which sound waves pass, as the molecules are spaced farther apart and need more time to jostle each other.)
History channel did a story about a town in California,(Parkland) on the San Andreas Fault ,that has an earthquake every 20 years. They had cameras set up and waited. It came late but they got it . It just showed a bunch of trees and land shaking and vibrating.
That’s essentially true. The velocity of earthquake waves varies greatly depending on medium, but air is far slower than rock.
As written here, P-waves travel at 5000 m/s in granite versus 330 m/s in air. S-waves, which only travel in solids, are about 60% slower than P-waves, so about 3000 m/s for granite. Surface waves are a little slower, about 2700 m/s for granite.
If you think about it, if it really was possible to hear earthquakes coming it would have been fairly easy to create some sort of earthquake warning system. Unfortunately, the best we have right now uses P-waves and it’s not clear just how useful they really are.
(Missed the edit window)
Here’s a news broadcast from a recent large earthquake in Japan. There’s a shot from the top of a building, and later helicopter shots of aftershocks. I don’t think that’s quite what you were looking for though.
(By the way, we just happened to be woken up this morning by a medium-small earthquake. Not a very nice way to start the day.)
(Apologies if hijack.)
I have been meaning to ask about earthquakes for a while.
If surface movements can be approximated as sine waves in up to three dimensions, what are the ranges of frequency and translations that are typical? (I can also imagine that some are one-time jumps, with some decaying vibrations following.)
A follow up question to those of you who have experienced them first hand: Can the velocity and movement make it impossible to stand? I.e., can they knock you off your feet? Could you find yourself curled up in a fetal position, struggling to hold on to a few blades of grass? Could they bounce you up and down on the ground?
(Thank Og the New Madrid fault hasn’t erupted in the last 200 years - it could be a big one when it goes again.)
There’s a huge range, from imperceptible to, well, something like this. I’m pretty sure that you would have had difficulty standing on that road. I know several people who were thrown to the ground during Mexico City and Kobe earthquakes.
Here, rather than the Richter scale, earthquakes are measured by their surface movement. In the link, you’ll see that the higher levels have descriptions like “Some people find it difficult to move” and “Thrown by the shaking and impossible to move at will.”
I couldn’t begin to tell you the mechanics of it, but we definitely heard it before we felt it. Maybe we were hearing leading waves that were intense enough to create a rumbling but not to feel. Who knows. But we heard something, looked at each other, then my orange juice almost fell over.
A real-world earthquake isn’t necessarily a single shock moving at the speed of sound through the earth. There can be a whole series of shocks of varying intensity, sometimes over a considerable time. So it would seem possible to have one that produced sound, then another that was enough to perceptibly shake a building.
In his notes during the voyage of the Beagle, Charles Darwin describes being in Valpariso shortly after a severe earthquake. Some people were unable to stand on open ground; some had injuries from being bounced around.
That was some nice video. The show, a segment of How The Earth Was Made will next be on Feb 28th. Set your TIVO.
I started a thread awhile back about experiences with dynamic geology. One poster to it mentioned sitting near a mountain peak and hearing the rumbles of an oncoming earthquake as it moved across the terrain toward her. Too cool.
As to how she might hear it before feeling it, I wonder if it wasn’t occurring in sections, the release of one fault segment causing the subsequent release of the next. Even if so, that of course wouldn’t always be the case.
While I hate to disagree with you folks, I can tell you that in some circumstances one can hear it coming. It’s not enough time to take any precautions, however, unless you recognize what you are hearing.
The 1965 Anchorage earthquake (9.0) made a lot of noise before we felt it. Whether it was the collapsing earth approaching us, or the actual sound of the fault slippage, I couldn’t say, but it sounded like a freight train bearing down on us. There was enough time for my mother to say “Earthquake!!” and my father to reply “Aw, bullshit!” before all hell broke loose.
More recently, about ten years ago I worked in an office in the eastern part of Anchorage, near the Chugach Mountain Range. I was sitting there one day when I heard a distinct pair of booms, which I would describe as similar to the sound of outgoing artillery or perhaps a jet’s sonic boom. Then the building started shaking. I didn’t really associate the two at the time, as I’d never heard the phenomenon. A few months later, the same thing happened; I realized that I was hearing some sort of preliminary sound/shock wave to the earthquake. The third time it happened, I immediately ducked under my desk and rode out the temblor down there. I don’t know why we could hear those booms: perhaps the mountains were amplifying the noise of the fault slippage. I’ve never heard it since I left that area of the city.
There were a lot of witnesses to these events who described the same experience, so I know I’m not imagining things.
I don’t have my notes handy, but I recall that buildings certified for seismic activity in my area have to be designed to withstand around .3g in the transverse direction.
That one was of my Dad’s favorites to talk about in class (he was a Structural Civil Engineering professor). I’d love to hear the story from an eye-witness’ perspective (hint, hint).
My mistake: it was Good Friday, March 27, 1964. I’m truly losing my mind. As for your request, I don’t think this is the right forum for that sort of story-telling. I may have related my experience in a past thread, but have no idea when, or what that thread may have been about. Perhaps the opportunity will arise again. I also have a friend who was in Kodiak when the tidal wave hit the town.
My earthquake experience doesn’t compare to Chefguy’s, but I once heard one coming* and *going.
I was sitting in a meadow in the high Sierra. I heard a low rumble off in the distance to the west; the rumble grew closer, then I felt the ground shake under me for a few seconds; after which the rumble continued on up the valley …
Twoflower, your experience and post was the one I was referencing. As a geologist I’d give anything to experience that. Chef’s too.
Perhaps on a small scale. I can tell you that in a major earthquake, you’re only concerned with saving your own ass.
