Instructions:
This is a take-home quiz for each student to complete on their own. Please write your answers to these questions neatly on a sheet of paper and turn it in, labeled with your name. Rest assured, you can actually work out all four questions on one sheet of paper. It is crucial to include the units of any numerical answers you give. Numerical answers need no more than 2 or 3 significant figures. If you show your calculations I can give you partial credit; but no formal lab report format is needed.

Due date:
In class, Thursday March 12.

At a Nevada geothermal prospect it is important to image a range-front fault that may dip up to 50 degrees, at depths that will correspond to two-way seismic travel times of up to 1.5 seconds. The alluvium above the fault is expected to have a P-wave velocity averaging 2500 meters/second, so the 50-degree fault dip translates to a time-dip of about 0.001 second/meter.

1. Just above the fault in the sedimentary section you would like to be able to distiguish two reflectors that are separated by a vertical distance as short as 10 meters. What is the minimum seismic frequency that you will need to observe the reflections with, to achieve this vertical resolution? Assume you will be able to collect very clean data with no noise.

2. To collect seismic reflection data on the fault at the frequency you computed above, what will be the maximum subsurface spacing for your survey?

3. What is the maximum migration distance you will have to account for? Imaging the fault will require that a receiver line be extended the length of the migration distance, with the receiver spacing you computed above for the maximum subsurface spacing. So the number of receivers ng that have to be "live" during the recording is the migration distance divided by the subsurface spacing. If ng is up to 48, we can do the survey ourselves. If ng is up to 256, a local contractor like Zonge can do the survey. If ng is up to 2000, we need a national contractor like Dawson from Colorado, Texas, or California. If ng is more than 2000, only one company can handle it, ION, at huge expense. Who will do this survey?

4. The ability to collapse Fresnel zones of horizontal resolution down to the quarter-wavelength Widess criterion depends on how well we can assess lateral seismic velocity variations. It might cost $100,000 for Optim to apply full-strength velocity analysis to our 3D survey. If we have to be cheap, not contract with Optim, and live with the Fresnel zone, how wide will it be for a drill target at the maximum 1.5-second time-depth? That width will be our location uncertainty for any targets.