I am working on a seismology assignment and it starts with the fundamentals of seismology such as the wave equation, the slowness... such as the question below:
write an equation describing the horizontal slowness (reciprocal of the velocity). This becomes a vector quantity for propagation in multiple directions.
I haven't fully grasped these concepts yet. And I looked around for lecture notes and this is what I found: MIT-introduction to seismology and
I am not sure which one is the answer to this question or what is even the difference between the two because they both seem to represent the slowness