Earth Science Geophysics / Hydrogeophysics

Discussion in 'Earth Science' started by Zsandmann, Sep 1, 2004.

  1. Zsandmann

    Zsandmann Premium Member

    I would like take take a little time to tell everyone about what I do. First off Im simply a geophysicist. A geophysicist is a scientist that uses remote sensing equipment to get a visual picture of the earth's interior without ever digging a hole or picking up a rock. It is very uninvasive. So that is the basics, now I will go a little more in depth on what I just discribed and lastly, I will talk about what exactly I do in the geophysical field. The other title of this thread Hydrogeophysics is what I am actually studying and that is when you apply geophysics to the study of groundwater to develop models for flow mapping, contamination movement, and remediation.

    So Geophysics. Geo refers to geology, the composition of the earth. Geophysicists look at earth structure from shallow crust (to look at water tables, petroleum fields, natural gas) to deep crust (faulting, structure, mountain building, rifting) to deep mantle and even the core (tectonic modeling, hot spot mapping, etc.) The latter deep core and mantle can only be studied by harnessing natural phenomena such as earthquakes. More on this later.
    Physics. Pretty obvious here. The physics come in to play when trying to described waves such as seismic waves propagating through the earth. Wave theory and other geophysics requires at minimum an understanding of calculus with an emphasis on derivations and integration. Also some differential equations are needed to fully desribe wave movement.

    Now I said I use non-invasive remote sensing methods, what exactly are those? Firstly, most people have heard of a seismography and seismology from the study of earthquakes. Geophysicists use seismometers to 'see' underground. If we are imaging shallow crustal features we will line up a bunch of small seismometers called geophones which are basically little springs that vibrate with the seismic pulse as it goes by and turns this into a digital readout that looks like a squiggly line as you have probably seen before. There are now two ways to see the crust. First we can take a sledge hammer and hit the ground, second we can set off an explosive charge such as a stick of dynamite, this depends on how deep we want to see and how small a feature we are looking for. When we set off the 'seismic source' it sends seismic wave into the ground. They go in all directions, now when one hits a boundary say between a sandstone and a limestone the rock properties change and some of that seismic energy is reflected off that interface and sent back up. It is recorded at the surface on the geophone as a spike. So we have the time we set off the seismic source and the time the spike arrived at the geophone, thus we can calculate how deep that interface is without ever digging a hole to actually see it. Now as I mentioned earlier some geophysicists study the mantle and core. Obviously a dynamite or hammer impact are not going to reach that far, BUT an earthquake will so those scientists use the recordings of when earthquakes are felt at different point around the world compared to when the quake actually occured at the epicenter to visualize and model the depth and compositions of these strata.
    Another remote sensing technique we use is Ground Penetrating Radar. It works just like the ones the airport uses to find planes We send a radio wave into the ground, it hits a transition and bounces back to the reciever. We use GPR to visualize very shallow features around ~20m or less.
    We also use DC resistivity to tell the composition of the rock underneath our study area. You send a current into the ground and measure it at different distances from the source. THe voltage drop between those points tells how resistant the rock is. Porous rocks filled with fluid and shales are less resistant than solid rock and sandstone.
    There are other methods we use as well that I know less about, there are gravitometers that measure the difference in gravity from one point on earth to another. The higher the gravity the more dense the rock underneath. Obviously some rocks are more dense than others. Approxamately and with some overlap from least dense to most dense.
    salt-sedimentary-carbonates-metasedimentary-igneous-metaigneous-crystalline(eg granite)-ORE bodies

    Ok so you suffered through my geophysics background now what do I do. Im a hydrogeophysicist, I use the above mentioned methods to study aquifer systems and ground water flow patterns. An aquifer is an underground body of water confined below by some nonporous rock that will not let it seep away into the ground. Most aquifers are sandstones but even solid crystalline rock can be an aquifer if it is broken or fractured and joints enough to hold water.
    My thesis involves using seismic, GPR, and DC resistivity to image a buried fluvial channel in Mississippi. The channel has filled in but even so it is acting as a preferred drainage route for groundwater. With the GPR I can actually draw a map of what the channel looks like underground, its quite amazing. I will put my abstract on here tomorrow.

    This is Jerry Bowlings paper on the area I am working on, he is at the University of Alabama, where I got my BS in Geology.

    The Society of Exploration Geophysicists
  2. JcMinJapan

    JcMinJapan Premium Member

    Wow, sounds very interesting as a position.

    After you graduate, what types of jobs do you usually get? Something in the oil industry to find the best location for oil, or the government side or research? Basically... what do you people do? ha ha ha
  3. Zsandmann

    Zsandmann Premium Member

    Well I personally am going for a job as a groundwater remediation consultant. Here in the West where water is scarce geophysicists map out aquifer systems and look for waying to maximize water use. But yes the oil industry uses GP's for oil and gas exploration, its cheaper to remote view than to drill a test well. Also GP's are hired in ore exploration and in acedemia as teachers, and there are always research grants and such for study of things such as the deep earth composition and rifting.
  4. Zsandmann

    Zsandmann Premium Member

    My thesis abstract

    Ok this is a rough abstract but it should give you some idea of what im doing.

  5. junior_smith

    junior_smith Premium Member

    ahh that is amazing sand its always good to knwo a geophysicst i say, well i say now

    anywho, would it be possible sometime if my organization needs a geophys guy could we use you? i don't knwo about your prior obligations or contracts but it would be good tohave a personal someone to use.
  6. Zsandmann

    Zsandmann Premium Member

    I dont mind answering questions, what organization?
  7. junior_smith

    junior_smith Premium Member

    this is soo cliche and it makes me sound like a moron, but right now yo don't really need to know.

    it's a good organization and that is at its truth, it pretty much stands for the same thing as ID does and that is light truth and knowledge with and emphasis on trith.

    if we require your services you will leanr more

    i really sound like a right [EDIT] lol

    ZS: Sounds good :)