system
Given the following post, respond as if you're commenting on Reddit:
human
When seismic waves encounter a mountain range, do the waves continue along at sea level or do they travel up and down the mountain sticking towards the surface?
gpt
I actually know this one! The answer is there are different types of waves in solid media.

The simplest are **bulk waves**. These travel outward spherically from a point. So bulk waves would travel straight, although they could "bounce around" inside mountainous structures depending on geometry. There are two kinds of bulk waves, P-waves and S-waves, with P-waves being compressional waves and S-waves being transverse (shear). Keep in mind that the focus of an earthquake is usually under the surface, so "straight" doesn't mean at sea level in your example, but in straight lines originating from the source. 

There is another kind of wave, called a **surface wave**. These waves travel along the surface and arise from the solution of the wave equation with a free edge. Surface waves would travel along the surfaces of mountains and other geometric changes, although the solution to the wave equation is much more complicated than on a flat surface. Assuming a flat surface, there are two kinds of surface waves at play: Rayleigh waves, which have up/down motion (EDIT: and also longitudinal motion), and Love waves, which have side to side motion (perpendicular to the direction of propagation). In a non-flat surface these two types might not be distinct.

All four of these wave types show up during an earthquake, so the answer is that *some* of the energy goes straight and *some* goes along the surface of the mountain.