Cathryn,

I don't remember posting about gravity. Certainly there are small spatial variations in gravity and small temporal changes in gravity.

With regard to the rings, the Earth is primarily radially layered. There are somewhat predictable zones of amplification and de-amplification that are a function of distance from a seismic disturbance. However, beyond about 40 degrees, the amplitude of the seismic waves primarily simply diminishes with increasing distance.

There are no secondary peaks that are large enough to trigger enough seismicity to easily see. The water in the oceans is too shallow to affect the seismic waves much, and the lateral variations like continental roots versus oceanic mantle are a second-order effect.

So if seismicity shows up anomalously frequently at particular distances, one cannot resort the Earth structure to focus energy at those distances.

John