What geological occurrence creates an 'fault line'?

erosion

earthquake

volcanic activity

Generally, an earthquake is the geological occurrence that creates a fault line.

Explanation:

A fault line occurs when the tensional stress in the rocks transcends the elastic capacity of the rocks and a fracture is caused. For a fault line to occur, there has to be a tensional pressure. When a tremor or an earthquake invigorates the tensional pressure from the rock to be released, a rock cracks up in two parts and a fault line appears on the Earth's surface.

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference. 

Ibelieve the answer is c also i'm in k12 too