Weight differences (all data from wikipedia:
The earth-moon (centre-to-centre) distance is about 30*Earth's diameter, and so about 60* Earth's radius.
So standing on the Earth's surface you're about 59 Earth radii (R) from the centre of the moon.
The lunar mass is about 0.0123 Earths

Your weight on the earth's surface is given by F_earth = G * m_you * m_earth / R²
The force of the moon pulling up if it's right above you is F_moon = G * m_you * 0.0123 * m_earth / (59R)²
F_moon=0.0123 / 59R² * F_earth = About three parts in one million of your "normal" weight

Andrew, no idea whether a 3 parts in one million change in the gravitational force would be enough to release geological strains. Not, I wouldn't have thought, unless they were pretty hair-trigger anyway. No doubt there is a huge amount of data available that would in theory allow it to be tracked, if anyone's got the computing power to trawl through it, after all the moon's path is pretty well understood (and indeed predictable) and a lot of data gets collected on geological events I believe.