Attached you should find two files. Reno.DTA is a data file with a real gravity anomaly for an east-west profile across Reno. You can read that profile into the gravity program that I distributed - grav2dc. The homework exercise is to try to fit this profile as well as you can.

To give you a start, use a density contrast of -0.33 gm/cm^3 for the basin sediments. Also note that this profile is Bouguer anomalies, and as we discussed in class the overall Bouguer anomaly for the Reno area is about -100 mgal, so the baseline is near there. In my experiments with this program, what I've found is that the best way to deal with that offset is to put in an "infinite slab" like what we discussed in class. This is just a fictitious density anomaly that you can insert below anything of relevance to this profile in order to get the baseline level right.

The second attached file, "jga-reno1.mod", has a start at modeling this data in case you have trouble getting this far. It has a fictitious infinite slab to get the overall negative Bouguer anomaly. It also has the start of a model for the basin - namely a body defined with four points and with a density contrast of -0.33. This starting body has only four corners, two at the surface at the edges of the profile and two below to form the start of a basin. If you want to use this as a starting point, you will need to add more points to the body to make the bottom of the basin a more complex shape that might eventually fit the gravity profile.

I'd like to also more clearly define the other gravity questiion that I asked you to work on with grav2dc. This is to find the gravity anomaly profile across the boundary between two compensated density-depth profiles. To be specific, please take the two compensated density profiles that we used as an example in class. You can build those precisely in grav2dc. Then find the Bouguer gravity profile that would be observed in a survey going across a sharp boundary from the one model to the other.

Good luck. If you have any questions, please email me or stop in my office. I will be on travel from Wednesday afternoon through Friday.