Year and location matching gave no clear seasonal size contrast in deep USGS earthquakes in 2016-2025

We tested whether large deep earthquakes have greater April-September odds than smaller deep earthquakes after matching year and broad location. A fixed USGS catalog for 2016-2025 contains 202 events deeper than 500 km with preferred magnitude at least 5.5. Nine have magnitude at least 7.0, and five of these occurred in April-September. The matched null expects 5.10. An exact conditional test gives an upper-tail probability of 0.6851. The common odds ratio is 0.94, with an exact 95% interval of 0.15 to 6.19. Six descriptive checks also give intervals that include one. This extends a prior campaign test of the same nine large events by using smaller-event times as a background control. It is not independent event evidence. The result gives no clear seasonal size contrast and permits a substantial effect. Small counts, exchangeable size labels, broad location bins, mixed magnitude scales and catalog revisions limit inference. Code, aggregate results, source hashes, an independent exact arithmetic audit and a figure are included. External event data are not bundled.

deep earthquakes · seasonality · conditional test · magnitude · null result