chris
when major planets changes the direction(though apperent from earth),the tidal force due to them on magma suddenly changes. Thus,either it accelarate or retard the motion suddenly.This ultimately,creates imbalance inside the crust.
Given the above condition exists,when a major tidal force of Moon joins,it act as a trigger for the quakes.
I do not know what is unscientific about this?
regards
Amit