Exercise 15
The granite that forms a small peninsula (Google Earth image at the top-left of the image below) on the coast of São Paulo State, Brazil, faces the Atlantic Ocean. The granite bears three subvertical fracture sets, two of the fracture sets strike approximately N15E and N75E as shown in Photograph (a) which was taken looking NE. The third fracture set strikes N45E as shown in Photograph (b) which was taken by looking SW. The third set is subparallel to the elongation of the peninsula. Answer the following questions.
a) What typical patterns do you observe in Photograph a and in Photograph b?
b) What fracture types do they imply? What is the orientation of the principal stresses and the tectonic regime?
c) What fractures seem to be more persistent?
d) Does this observation have implications for flow?
e) What can you say about the fracture connectivity?
Photographs (a) and (b) were taken from the red star looking toward NE and SW, respectively. Photographs from Ubatuba, São Paulo, Brazil, by Amélia Fernandes