The University of Washington has a new map of Mercer Island's geology. I don't see anything particularly unsettling (so-to-speak)about our neighborhood:
We're sitting on "Vashon subglacial till" (purple), which is between Vashon recessional deposits (orange) and "Pre-Fraser non-glacial deposits" (green). The jagged lines near us are "scarps", which in our case are those big dirt cliffs behind our neighbors across the street.
No fault lines, no artificial fill: just nice glacial deposits from the Pleistocene Era.