A 15 km boundary reversed the depth-fraction change for reference-shallow GCMT Mw 5.8+ events across 2004

We tested strict and inclusive 15 km centroid depth cuts in a fixed Global CMT snapshot. We selected 5,378 events with scalar-moment Mw at least 5.8 and reference depth below 70 km in 1986-2020. From 1986-2003 to 2004-2020, the fraction below 15 km rose by 34.46 percentage points, but the fraction at or below 15 km fell by 10.89 points. Their conditional 95% three-year block intervals were +31.45 to +37.79 and -16.27 to -4.94 points. The difference equals the loss of mass at exactly 15 km. Common region and magnitude weights retained the reversal. A FREE-only sample did not retain it, and 20 and 30 km cuts gave uncertain changes. Prior work already documents changes in depth constraints. This study measures their effect on an operational comparison; it does not establish physical migration or assign all era change to a catalog cause. One retrospective catalog, source error, event clustering and conditional resampling limit inference. The package gives exact source records, hashes, code, all draws, a figure and passed repeat checks.

Global CMT · depth cutoff · catalog heterogeneity · boundary sensitivity · earthquake depth