Well, if I got it right, 1 bar= 1 atmosphere=10 m of water.
density of water=1, density of granite=2/.65. So, 1 km of granite is 265 bars..so ten km is 2,650 bars (lets see...I think this is some number of mega pascals...but I can't deal with that).
But, it is not the total stress that causes earthquakes...it is differential and/or deviatoric stress (I forget the difference and my library is still in boxes..). Stress drop during an earthquake is usually 100 bars or less. So, 1/2 bar is quite a bit. But, yes, we already discussed on this thread that the 1/2 bar at the seafloor may not be seen as differential stress at the depth of the earthquake...need someone who understands how this might work to post...

Now, I could use a bar.
Chris