What the numbers are
Epicenter distances use the haversine formula on a sphere of radius 6,371 km and the coordinates in the USGS table of the 20 largest earthquakes since 1900. Volcano distances use the same formula and the Smithsonian snapshot. Rectangle distance is zero when the point is inside a lat/lon box, and otherwise the haversine distance to the closest point of the box (the coordinates clamped to the box). That matches how the boxes are defined: edges of constant latitude and longitude, not a geodesic polygon.
The San Andreas fault and the Cascadia megathrust do not have a vertex in that USGS top-20 table. The 1700 Cascadia earthquake and the 1811–1812 New Madrid earthquakes predate the instrumental list. Do not read “distance to the Cascadia rectangle” as distance to the locked fault. Read the San Andreas and Cascadia pages for what we can say without inventing a line.
Worked examples to try
- Mount St. Helens (already filled in) should fall inside the Cascadia rectangle, so that edge distance is 0 km.
- Kīlauea’s preset should fall outside every rectangle.
- The 2011 Tohoku preset should sit close to the Japan / Ryukyu rectangle and exactly on its own epicenter (0 km to that epicenter).