Once upon a time, when I was still in-school, we had a small ground penatrating radar (GPR) unit. As part of our lab work, we went to a garden on campus and proceeded to map the sub-surface using the unit.
What we saw was that the ground we surveyed was solid for about 30 feet, but then it seems that the ground gave way to a void after 30 feet. We found out later that the void was actually the underground causeway between two buildings. People use it to walk from one building to another. Kind of like the underground tunnels in downtown Houston. GPR can be used to map caves that are not too deep below the surface as it has a limited range into the ground. I don't remember how deep the limit is. If you want to map deeper undergroud, you use various forms of seismic, up to the center of the earth, even to the other side of the globe! On Thu, 15 Nov 2007 10:25:09 -0800 l...@alumni.sfu.ca wrote: > Hi Dave, > > Petroleum geologist and geophysicists have been using various seismic > methods to map the sub-surface since the end of WWII (plus/minus). > > The new ship probably has a more advanced/more capable version of an > old technology. > > There other technologies. There is ground penetrating radar. There is > EM, magnetic and gravity survey techniques, to name a few. > > For example, the ground directly below a big cave would have less > gravity because gravity is related to mass and if you have a void, > there will be less gravity. You weigh less (just a very tiny bit) > standing on the surface above a big cave. You can measure this slight > change in gravity to determine what could (speculative) be underneath > the surface. > > It's called geophysics - the application of the laws and principles of > physics to the study of the earth. Being in Texas, there are a lot of > geophysicists around that can help explain how you map the underground > using various technologies. I'm not one. Perhaps there is a > geophysicist on this mailing list that can explain a bit more. > > > > On Thu, 15 Nov 2007 11:12:41 -0600 dlocklea...@gmail.com wrote: > > There was something in the news this week about the launching > > of a big research vessel that would map the underground layers of the > > earth as it traveled around the ocean. I barely caught a glimpse > > of the news story, but it indicated they could map deep voids in > > the earth. > > > > If this is true, do geologist have a similar device to map > > caves from a surface driven vehicle? > > > > Or is the technology old news? > > > > Or did I miss something? > > > > David Locklear > > > > --------------------------------------------------------------------- > > Visit our website: http://texascavers.com > > To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com > > For additional commands, e-mail: texascavers-h...@texascavers.com > > > > > -- > Lyndon Tiu > > --------------------------------------------------------------------- > Visit our website: http://texascavers.com > To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com > For additional commands, e-mail: texascavers-h...@texascavers.com > -- Lyndon Tiu --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com
