Final answer:
The type of fault when tectonic plates move past each other in opposite directions is a transform fault, a kind of strike-slip fault. The San Andreas Fault is a famous example of such a fault where the Pacific and North American Plates slide horizontally past one another.
Step-by-step explanation:
When tectonic plates move past each other in opposite directions, the type of fault that occurs is known as a transform fault. This kind of fault is characterized by the horizontal motion of the blocks on either side of the fault line. A well-known example of a transform fault is the San Andreas Fault in California. It's a site where the Pacific Plate and the North American Plate slide past each other horizontally. Unlike other types of faults like normal faults and reverse faults, transform faults do not involve significant vertical movement, meaning that one block does not move over or under the other. Instead, the movement is primarily lateral.
There are several kinds of faults, each characterized by the direction of movement between the blocks. Normal faults occur when the crust is being pulled apart, causing one block, the hanging wall, to slip downward. Reverse faults happen when the crust is being compressed, leading to the hanging wall moving upward. Both are subtypes of dip-slip faults due to the vertical motion. Strike-slip faults, on the other hand, mainly experience lateral horizontal movement. The answer to the question is thus a transform fault, which is essentially a type of strike-slip fault where the tectonic plate movement is horizontal and alongside each other.
Given the definitions and examples of faults, our final answer is: (a) transform fault. This fault type is evidenced by the San Andreas Fault's activity, marked by frequent earthquakes due to the lateral sliding past of the Pacific and North American plates.