Seismic Prospecting

lcp1992

Does somebody know what is seismic prospecting? and where can I find more info about it

davenn

hi there

have you done any google searching using that term, or seismic profiling ?

But to get you started ...

Basically its the its the process of emitting sound energy into the earth and recording the reflections of those sound waves off the various rock/sediment layers in the earth.

The sound is generated by either small explosions or by trucks with large ground thumping/vibrating units on them .... google search Vibroseis truck

strings of many geophones ( small seismometers) are layed out along the surface of the ground and they record the reflected waves

ok here a photo of a couple of my seismic surveying geophones with a ruler to get an idea of scale :)



cheers
Dave

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lcp1992

Are seismic prospecting and seismic profiling related? or do they mean the same?

davenn

here's an example of a seismic profile, this one done at sea showing the layering below the seafloor



When I did Geology at university, there was a lot of offshore surveying done around the local coastline, which was great for us students as it gave us first hand experience in creating the seismic profiles, then later on learning how to interpret them with help from the lecturers

cheers
Dave

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davenn

you have to do the profiling BEFORE you can do the prospecting

ie. its the profiling that gives you the information on what lies below, where oil /natural gas can be trapped etc That trap is usually at the top of an anticline and nees the right overlaying rocks/sediments to keep the oil etc trapped so it doest dispurse upwards any further

here is a basic drawing of an anticline....



Dave

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johnbbahm

There is a lot that goes into the raw data to make it look like the graphs above.
The sound frequencies are mostly between 10 and 110 Hz.
The main orag. is http://www.seg.org/seg
Basically you send out a signal and look at the echo with a BIG array.
By comparing the signal from physically separated geophones/hydrophones,
you can determine depth and density of layers.

davenn

Yes there is bit all the recordings from the many geophones, as I stated, build up the picture :)
The freqs looked at are not really much more than 20Hz since the geophones used are usually resonant between 5 and 15 Hz. Those 2 profiling geophones I showed above are resonant at 8Hz. They are out of an array of 100 geophones.

Dave