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is it possible to find empty spaces i.e. caves in solid rock through siesmology. the way my professor described it to me is that the ground waves would slow down passing through air, is there way to record the differences in speeds and possibly visualize the space?

Paul Siegel

It is problematic,but possible.
You got me Googling,so here's an interesting link:
http://www.naturalgas.org/naturalgas/exploration.asp

You can rent GPR units for $150-$250 per day,pricey for an individual,but a large organized project could afford it..

GPR (Ground Penetrating Radar) ain't the same thing as seismic.

Actually, in theory, you can use electrical resistivity, electrical magnetic, seismic, ground penetrating radar, and micro gravity to locate underground voids, old excavations, and near-surface faults. All have some kind of limitations, some work better in different conditions than others, and all can give you false data. The data from all should be confirmed by drilling bore holes.

Which means, in my opinion, that direct exploration of the underground void is still the best way to go.

George Dasher wrote:Which means, in my opinion, that direct exploration of the underground void is still the best way to go.

As well as the most satisfying.

obviously surfaced based exploration into caves is the way we all would prefer. but is it possibly that there are caves that are not possible to access from the surface? potential spaces in the ground that would require an artifical entrance. what i was thinking when i posed the original question, is that it would be a (relatively) easy way to visualize possible connections between caves. instead of lugging a GPR far into the nether reachs of a cave it could be done above ground (relatively) simply.

Also, you could use such things to search for cavities before building on property. Very effective, I think.

Paul,

GPR really isn't simple and requires training to interpret the data correctly.

There is a commercial cave in Germany (north of Weisbaden) that has no natural entrance. The owner discovered it when drilling for a well. He then drilled a 6 inch shaft and lowered a cylindrical panaramic camera to have a look. He then proceed to excavate a large sloping tunnel to the void below.

A few of us Euroregion Grotto cavers assisted him with digging open some more passage. The cave is not too bad either.

Hmmmm...wonder if I can find it on the web? I don't remember the name at this point since this was back around 1977-1978.

Ahhh..you gotto love the web! Here it is: Kubach Crystal Cave
http://www.showcaves.com/english/de/showcaves/Kubacher.html

I think there are many caves without known human entrances--caves that have only groundwater and/or critter entrances.

And there are probably many caves without any entrance whatsoever.

George,

Bill Varnedoe made an estimate many years ago on how many caves there were with no entrances based on the distribution, etc. of caves then on the Alabama Cave Survey. But, it remains an unprovable number so what's the point?

Paul -

There are two main kinds of seismic surveys - reflection and refraction. In reflection surveys,
sound waves are sent vertically into the earth. When the wave front encounters an interface the
wave is reflected back to the surface where seismometers (specialized microphones) pick up the
sound and the travel time is recorded. This method is worthless for cave detection. In refraction
seismic surveys, the sound waves that travel downward at an angle to the surface. When these
waves encounter a rock layer that conducts sound waves with a higher velocity, the wave is
refracted (meaning the direction of travel changes) and travels essentially horizontally along the
top of the rock layer. The wave is also refracted back to the surface where several seismometers
record the signal. Using the times of travel, geophysicists can deduce what lies beneath. (This is
a greatly simplified explanation - experts please don't jump on me.)

I believe your professor is talking about using some modification of refraction seismology to
detect caves by sending sound waves horizontally beneath the surface. Theoretically, this would
work. Practically, I can think of three problems. First, the sound wave you generate will travel
along the surface and reach the seismometers first, because it is the shortest path. In small
dimension surveys, such as what would be used in looking for caves, this initial hit on the
seismometer may still be ringing when the wave that went through the suspected cave arrives.
Separating the two events might be difficult, if not impossible. Secondly, the void would have to
be quite large to obtain a difference in travel times that can be discerned from those waves that
did not go through the void. Thirdly, the earth surrounding the void is usually not homogeneous,
and may introduce extraneous results that are difficult to interpret (again, if not impossible).

On the practical side, the learning curve to interpret the results for lay people would be too much
to bother with. When you rent the equipment to do this survey, you would also have to hire a
consultant that has experience with the method. There are better ways to geophysically prospect
for caves. The best practical method IMHO, and fastest and cheapest, is resistivity. For shallow
caves, resistivity equipment can be built for a nominal cost, and with certain electrode arrays,
interpretation is comparatively easy. A magnetometer works great for most lava tubes, and if the
void is large enough, could be used with shallow limestone caves. This method is fast, easy to
interpret even for a lay investigator, and the instrument is cheap, compared to other geophysical
instruments, like $5,000 new. eBay has had them for $1K - $1.5K; don't know how good they
are. (Mine was free as compensation for extra time.) Most other methods work, but still require
a specialist to interpret the results, can be very time consuming, and use very expensive
instruments.

then the question then boils down to conservation: if we have the technology to find and access the caves do we, as responsible cavers, possible desecrate a pristine natural environment or do we leave them as is, of course then doesnt every explorer entering virgin cave face the same conflict?. this , i feel, is the key difference between conservationist and explorers. the key would be to find some morally acceptable middle ground, like only enter human accesible natural cavesand drill only for connections to enlarge presents systems.

another arguement that enters my mind could be the possible abuse of such technologies. it wouldnt do to have a pit drilled into every empty space and to connect caves that have no natural connections, but the possible discoveries would be enoromous.

does the nss have an ethics section yet?