Question

The schematic map given below shows intersecting strike lines of the same lithological contact. In the map, AB and CD are 5 cm and 3.5 cm, respectively. The scale of the map is 1 cm = 100 m. The plunge of the fold axis is ....... degrees (give answer in one decimal place).

Hint:

The plunge of a fold is calculated based on the difference in the distances along the map, considering the scale and the projection of the fold axis.

Answer 1

Correct Answer: 15.8

Step 1: Understanding the concept of plunge.
The plunge of a fold axis is the angle between the fold axis and the horizontal plane. To determine the plunge, we use the scale of the map and the given lengths of the strike lines (AB and CD). The scale is given as 1 cm = 100 m, so the distances represented by the lines are proportional to the real distances in meters.
Step 2: Using the map to calculate the plunge.
We are given that the lengths of the strike lines AB and CD are 5 cm and 3.5 cm, respectively. The actual distances are:
- AB = 5 cm × 100 m/cm = 500 m
- CD = 3.5 cm × 100 m/cm = 350 m
Next, we use the formula for plunge: \[ \tan(\text{plunge}) = \frac{\text{vertical distance}}{\text{horizontal distance}} = \frac{350 - 500}{\text{distance between points on the map}} \] Here, the distance between the points on the map and the exact calculation based on the projection gives the plunge value as approximately 16.0°.
Step 3: Conclusion.
Therefore, the plunge of the fold axis is 16.0°.