[M T]

Another way to think of it is that we live on layers of granular material (think sand) that tends to settle/compress over time.  Water (or other incompressible fluid) in that material, trapped in pockets, will perhaps change how fast it compresses. 

It seems to me that underground "rivers" or reservoirs where the water can flow in (and, thus, can flow out) shouldn't change that compression rate much since, under pressure, the water will flow out.  Of course, the pressure it takes the fluid to flow through the material will contribute to a difference in pressure of the fluid in different regions.

[M T]

Another way to think of it is that we live on layers of granular material (think sand) that tends to settle/compress over time.  Water (or other incompressible fluid) in that material, trapped in pockets, will perhaps change how fast it compresses. 

It seems to me that underground "rivers" or reservoirs where the water can flow in (and, thus, can flow out) shouldn't change that compression rate much since, under pressure, the water will flow out.  Of course, the pressure it takes the fluid to flow through the material will contribute to a difference in pressure of the fluid in different regions.