This is some earthquake triggering theory information which was included in a report which I just posted to a number of Internet Newsgroups regarding that earthquake triggering chart I am preparing:

There is what might be referred to as a "Pressure Wave" in the Earth's crust. And it constantly travels towards the west. When a Pressure Wave crest or trough hits an earthquake fault zone which has accumulated enough strain energy that it is about ready to fracture on its own and it does that at the right time and angle it can trigger an earthquake.

As the Earth and moon rotate relative to one another and relative to the sun they are both being constantly accelerated in various directions. That happens when objects travel in a somewhat circular orbit. And although the gravitational pull of the sun on the Earth is largely constant around the world, the pull of the moon differs by something like 7% from the side of the Earth facing the moon to the side of the Earth facing away from the moon. When the Earth is experiencing times of maximum acceleration in space such as when the sun and moon are next to one another in the sky that gravity force difference tends to "stretch" the Earth more than usual. That then results in especially strong Pressure Waves and increased earthquake triggering activity.

My chart might not provide any information on this, but I suspect that the daily rotation of the Earth on its North - South Pole axis could also be important here. Because of that rotation a part of the Earth which is on one side of a line connecting the location on the Earth's surface where the combined gravitational pulls of the sun and the moon is strongest and the center of the Earth, is being accelerated in one direction versus the moon location in the sky. And a part of the Earth on the other side of that line is being accelerated in the other direction. Those conflicting forces might then affect the locations of the Pressure Wave crests and troughs.