A very good suggestion. Working on your idea will possibly reveal more new findings, especially with Detectors & Sonic Repulsers etc. If Archaeological Department works in this direction 'may be' they will be able to discover Hidden Moorththi's hidden and kept 'if any' in any underground Chambers, or of any underground tunnels leading to former Thanjavur King's Palaces 'if any'. What is happening regarding a news report on a well being drilled within the premises of the Temple recently which met some protests from the public fearing the weakening of the structure of the temple ??
I have read two methods in Geology to Identify the different layers of soil and water in our Geo Profile. One is Electric Resistivity method other is Seismic resistivity Method. This will give layer by layer information.
This happens to be my field, so maybe I can put in some more general information...
All these methods depend on some sort of penetration of the material (in this case, the floor/soil) with some energy, and seeing how that energy behaves. There are several techniques one can use, depending on what is under observation, and what we're looking for. The techniques I know of are:
1. Resistivity/Conductivity: This is good for loose soil and metals, but pretty much worthless for stone. Also, it can't really penetrate deep into the material.
2. Impact echo/seismological testing: This is the equivalent of tapping a box to see if it's hollow or not. Basically, you use a hammer or a ball to send vibrations into the object and listen for echoes. It's useful for finding the thickness of a solid object, and variations in that thickness. This would seem to be a good fit for the subjects at hand (stone blocks). Unfortunately, the deeper you want to go, the more heavy your impact should be. Since you have to move in a grid pattern for this, it's quite possible that this has an adverse effect on the structural integrity of the temple. On the other hand, it will probably be the best for actually giving something of a yes/no answer. This is also the most painstaking technique, since the hammer and microphone have to be moved physically from point to point to probe everywhere. A single reading is not of much use, since it's sensitive to noise. Many readings taken on a grid are usually put together to form an image, which shows the thickness under each point.
3. Ultrasound: Pretty much like impact echo, except that you use a probe to excite a high-frequency sound wave into the object. It's nice for smaller objects, but not really that great for the large depths we're talking about.
3. Ground penetrating radar: This is the same as the above, except that it uses radio waves (usually microwave) to do the pulsing. Again, the problem is penetrating power, but it should normally be able to go deep enough. GPR is excellent for finding metallic objects, especially when embedded inside another medium, and so, is probably good for buried caches.
granite walls/floors in Madurai, which would be on the edge of detectability for most common instruments. On the other hand, if the chamber is _within_ that 8 ft wall, there's a better than even chance of detection with the right equipment. These things are commonly used to test bridge decks of about 2 metres depth, so it's definitely plausible. But probably quite an expensive proposition if you're not at least reasonably sure that there's something to find. Personally, if you could guarantee that the superstructure can take it, I'd go with Impact Echo techniques for something like this, with the second choice probably being GPR.