Shallow and deep M5.5+ earthquake pairs showed no clear one-day excess within 500 km under annual time shifts in 2000-2025

We tested whether shallow and deep earthquakes occur close in space and time more often than expected under annual relative time shifts. We used a fixed global USGS ComCat snapshot for 2000-2025. Shallow events had depth 0-70 km. Deep events had depth greater than 300 km. Both had preferred magnitude M5.5 or more. The primary count was 26 cross-depth pairs within 500 km and one day in the same year. In 9,999 shifts of the full deep series within each year, the mean count was 24.32 and the central 95% range was 13-44. The two-sided Monte Carlo p-value was 0.7292. Ten shallow events followed deep events and 16 preceded them, counting pairs. Radius, time-window and split-period checks gave no clear excess. This is a conditional null result for large-event coincidence, not proof that deep and shallow systems are independent. The shift model changes relative seasonal phase and cuts clusters at year ends. Sparse counts, mixed magnitudes, location errors and catalog revision limit inference. Code, aggregate results, shift draws, an independent count audit and source hashes are included. External event records remain outside the package.

earthquakes · cross-depth coincidence · circular time shifts · null result · ComCat