The Shower pan is technically that device which keeps the water from going everywhere. The bathtrap area is the area in the picture with the pipes letting the water go to the plumbing and out of the house.
Now visualize the termite people coming out to spray under the slab before its poured. That show box size area is higher with dirt and when the plumbers come in to finish they take away dirt. They also take away any trace of liquid termiticide and therefore = termites.
See the termite tube in the right side of the hole, that is how all the damage occurred. Inspect, investigate and then solve the problem. In this case impossible to see the shower pan so a surprise happens. Call ProBest for an inspection today 480-831-9328 or 623-414-0176