What does it indicate if a professor from other departments is included in applied math department?
Affiliate faculty are common in many university departments. This indicates faculty who have a departmental home (faculty line, voting rights, tenure and promotion line, office space) but for a variety of reasons are given courtesy appointments (sometimes called in the USA as 0 FTE appointments) in another department. This may be because they teach a crosslisted course or occasionally sit on doctoral committees of the other department, or occasionally just for the academic lulz (ie, they requested an affiliation and there was no reason to deny it).

Affiliate faculty rarely occasionally (depending on discipline and university) serve as chairs of doctoral committees and similarly are rarely/occasionally (depending on discipline) given students in that department to supervise. Their ability though to sit as members on committees is useful if you were to want to do a project in geophysics (in this case) but otherwise you can ignore them.

Note that this is different from faculty with dual appointments where their faculty line is split (0.5 FTE in one department, 0.5 in another). They have voting and advisory rights in both departments.

FTE = Full-Time Equivalent, the essential counting unit of faculty lines. 
A department with two full-time faculty and two joint-appointments would 
have 2*1 FTE + 2 * 0.5 FTE = 3 FTE


TL;DR: Don't worry about affiliate faculty. Focus on the core faculty and their strengths when making decisions.