Nearby events within one magnitude unit were more common after 171 isolated shallow M7 to below 8 earthquakes in 2001-2024

We tested whether relatively large nearby events were more common after selected shallow earthquakes than before them. A fixed global ComCat snapshot gave 171 centers of preferred magnitude 7 to below 8 in 2001-2024 after equal isolation on both time sides. Each center counted at most one success per side. A success had at least one event within one magnitude unit of the center, within a 300 km hypocentral chord distance, at least one day and less than 30 days away. There were 30 after successes and 14 before successes. The paired fraction difference was 9.36 percentage points, with a conditional 95% three-year block interval of 2.78 to 16.38 points. Radius, isolation and spatial resampling checks retained positive primary intervals. A half-unit gap and days 7-30 alone gave intervals that touched or crossed zero. Most centers had neither event. The primary excess thus remains when rich sequences cannot contribute many successes per center. It does not identify causal aftershocks, test the mean Bath magnitude gap or give a hazard forecast. Selection, sparse discordant centers, catalog revisions and dependence limit inference. The package gives code, aggregate evidence, source hashes, a figure, independent count checks and replay instructions.

earthquakes · relative magnitude · temporal asymmetry · paired incidence · ComCat · mainshock selection