Shallow M7 pairs within 300 km showed no clear excess at 30-180 days under five-year shuffles in 1976-2025

We tested whether shallow earthquakes of magnitude 7 or more occur near each other at delays longer than one month. A fixed USGS ComCat record gave 530 events in 1976-2025. There were 44 pairs within 300 km and more than 30 to 180 days apart. We kept event dates fixed and shuffled locations within five-year periods. In 19,999 draws, the mean count was 39.80 and the 95% reference range was 29-52. The upper-tail p value was 0.25775. The result did not show a clear excess under this reference. The expected count rose to 70.52 for one-year periods and fell to 34.28 for ten-year periods. In contrast, 48 pairs occurred within seven days, against a five-year shuffle mean of 2.84. This small study gives a reproducible delay test and shows its dependence on the reference time scale. It does not exclude delayed interactions, test distant triggering, or estimate a change in hazard. Source rows, hashes, all pair lists, null draws, code, a figure, and a separate arithmetic audit are supplied.

earthquakes · ComCat · local clustering · conditional randomization · null result · reference sensitivity