Problem set #3, Fall 2005 - Due 10/10/2005

1. The attached spreadsheet has declination and inclination (D, I) measurements for a number of rock samples collected at one locality. Find the average declination and inclination by breaking each D, I pair into x, y, z components, averaging the components, and then transforming back to D, I space. This is the correct way to average vectors (e.g., (D,I), strike & dips, latitudes and longitudes, Euler poles, lineations, etc.)

2. Read: S.D. Sheriff and M.C. Stickney, 1984, Crustal Structure of Southwestern Montana and East-central Idaho; Results of a Reversed Seismic Refraction Line. Geophysical Research Letters, 11, #4, 299?302.

In that paper we develop a simple, two-layer refraction model for southwestern Montana. I want you t o assume the model is wrong in that there must a thin high-velocity (V = 6.8 km/s) layer (blind zone) between the upper crust and mantle. Assume our other velocities are correct, use our average Pg and Pn values, and that there really is three layers. The point here is you have to develop a 3-layer velocity model that honors our observed first arrivals and travel times. What is the thickest the blind zone can be without becoming a first arrival? Show me a graph of your result. How would you test your hypothesis?