Maps and Faults

Question

I'm having trouble determining the type of fault represented on this map.

1. What type of fault is represented on this map?

2. What is the fault orientation?

What does this mean?, Do I do this by working out strike/dip angle/dip direction of the line F–F'?. In the example I did in class, I was given the orientation every time and just drew the cross sections, so I don't know.

3. determine components of fault movement, i.e., work out dip-slip, strike-slip, net-slip, heave and throw

I know the formulas for each or how to determine some, but where do I have to start on this map? From what I can see I can maybe work out the throw first?

Throw = displacement of horizontal feature = 100 m?

Heave - slide said to use trigonometry

I can't find any examples online for the maths of faults and so I think I need a lot of help with this part if someone could work step by step. Because when I look at this map, I don't know where to start and where things are going by calculating those things. Thanks

I did a rough cross section of the map, but I don't know the orientation of the fault so I just assumed it was in that direction.

Answer 1

There are no dips given, so you have to work by pure geometric deduction. The sediment subcrops on the east side all seem to be roughly parallel to the contours, which suggests near horizontal stratification. On the western side the diorite-shale subcrop is higher, suggesting about an 80 metre downthrow to the east. The aplite boundary shows no curvature in the valley or hillslopes, suggestiong that it is probably near vertical. Therefore, from the scale bar you can estimate the horizontal displacement. You now have horizontal and vertical components, so you can calculate the displacement vector.

The aplite dyke is probably a late-stage crystallization of the diorite, and is obviously pre-fault, pre-basalt dyke. In fact the basalt dyke is the most recent feature, probably thrown in a s a red herring!