TEST YOUR KNOWLEDGE Answers on Page 30
Robert G. Font, CPG-03953
rgfont@cs.com
1. A type of “texture” one may expect to find in volcanic rocks is: a) b) c) d)
Dendritic Oolitic
Aphanitic Phaneritic
2. The foundation of “silicate minerals” (which constitute the most abundant mineral group found in the Earth’s crust) is the “silicon tetrahedron” where four oxygen anions bond to a silicon cation to create a radical with a valence of -4. What is the valence of the silicon cation?
a) +4 b) +6 c) +8
3. The seismic discontinuity that separates the Earth’s mantle from the Earth’s core is known as the: a) Mohorovic discontinuity b) Gutenberg discontinuity c) Bullen or Lehmann discontinuity
4. Consider a horizontal fault where Block X rests on Block Y. The force “F” is that which is required to move Block X over Block Y. Block X has a length “L,” a width “a” and thickness “T.” Let “U” be the coefficient of friction along the fault plane and “W” be the weight of Block X. Let’s also say that the lithologic unit which makes up Blocks X and Y has a density “p” and that the acceleration due to gravity is “g.” In our example, let L = 10 km, g = 980 cm sec-2, p = 2.70 gm cm-3 and U = 0.5. Recall that “stress” (S) is force per unit area. Based on this information, what value of “S” would be needed to cause motion along the fault?
a) 1.09 x 108 dyne cm-2 b) 1.32 x 109 dyne cm-2 c) 1.56 x 1010 dyne cm-2 d) Me, do this? No way, José!
5. In reference to question 4 and given a rupture strength of 5 x 108 dyne cm-2 for the rock which makes up Blocks X and Y (closer to what we may expect, in reality), what is the maximum length (L) of Block X that could be moved along the fault without it being potentially “crushed in place?”
a) L = 9.33 km b) L = 4.19 km c) L = 3.78 km d) Great Scott! Man, this is absolutely depressing!
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