05-04-2018, 03:39 PM
Tom: my reading of the USGS methods that Kirt posted is that since depth is (at least sometimes) calculated relative to sea level, an earthquake with a negative depth occurred below ground but above sea level. So for example this one: https://earthquake.usgs.gov/earthquakes/...#executive is centered just south of Halemaumau, at an elevation of 1100m, is shown as having a depth of -1.1km, which would put it close to the surface. There are a few close to or in the ocean that are shown with a depth of up to -0.6km, but those are all around the southwest rift where there's probably more error.