Roger
1)Tidal pull on ocean creates several meters of high tides.It is actually not tidal pull but the differential pull on water due to Moon as well as center of earth.this is only the reason why we get high tide at the opposite end of the earth.It also depends on volume of water it acts.More the volume more the effect of differential pull.This is again the reason why we do not have measurable high tide in a pond.
Now considering huge volume of semisolid fluids/magma in side the crust ( how many times more than ocean water?) it is also acted upon by the same differential pull. And in turn may have greater high tide (at X-X axis) and low tides( at Y-Y axis). when the these differential pull exceed the limit it creates thrust on earth crust from inside). When this pull comes beneath the weaker crust or fault line it break the crust. If it comes below a volcano mouth it can erupt a volcano, This is why the dates are also prone to eruptions.Now as earth moves in orbit and along axis it becomes difficult to pin point where and when it will be below a fault line
the quakes occurs at plate boundaries only because they are weaker section and breaks first

roger, what you are talking is force ,but it is deferential pull that water gains the tides.
what do you think,a force equipment to make mouse sneeze can move ocean waters by 4 to 6 mts high?

Amit