An unseen interior is declared empty
Hollow-Earth claims replace the planet’s deep material with a large empty space. Surface caves are real, but a local cavity and a planet-scale void make very different predictions for waves travelling through the interior.
Different waves reveal different materials
Compressional P waves pass through solids and liquids. Shear S waves do not pass through the liquid outer core. The changed wave paths, rather than simply an absent arrival, help identify the core’s physical state.
USGS describes a nominal direct P-wave shadow between angular distances of 104° and 140° from the earthquake. Refraction at the core changes the paths. A station in that band can still record other seismic phases: this is not a claim that its entire seismogram is blank.
Earth’s interior is layered, with crust and mantle over a liquid outer core and a solid inner core. A large central vacuum would need to reproduce the observed transmitted, refracted and reflected signals together, not only point to one missing direct arrival.
Put the shadow band on a surface-distance scale
For a spherical radius R, an angular separation θ corresponds to a surface arc s = Rθπ/180. The calculator converts the nominal shadow boundaries into kilometres and locates a chosen station by angular distance.
These are distances around the surface from the epicentre, not lengths of the bent paths inside Earth and not predicted arrival times. Move the station control to compare an angle before, within or beyond the direct P-wave shadow. Boundary values are reference markers, not a detailed earthquake travel-time solution.
Locate a station relative to the P-wave shadow
Enter the epicentre-to-station angle. Surface arc distance is not the wave’s underground path length.
Surface arc on the mean-radius sphere; not a seismic ray path.
Nominal near edge of the direct P-wave shadow.
Nominal far edge of the direct P-wave shadow.
The difference between the two reference boundary angles.
Working tape
- Radius × π ÷ 180
6,371.0084 × 0.017453 = 111.195073 - Station angle × kilometres per degree
120 × 111.195073 = 13,343.40879 - Near boundary surface arc
104 × 111.195073 = 11,564.287618 - Far boundary surface arc
140 × 111.195073 = 15,567.310255 - Far angle − near angle
140 − 104 = 36 - Angular width × kilometres per degree
36 × 111.195073 = 4,003.022637
The shadow is a material boundary, not an entrance
The 104°–140° reference interval spans 36° of angular distance. At the selected mean Earth radius it covers roughly 4,003 km of surface arc. The tool places the interval on a scale; the seismic observations supply its physical interpretation.
A missing direct P arrival alone does not prove a void. The pattern across P waves, S waves and other phases supports a differentiated interior and a liquid outer core. It does not support extrapolating small caves into a hollow planet.