Weekend daytime share was 8.28 points higher for northern Cascadia tremor detections in 2017-2025

We tested whether a reported weekend daytime excess remains in a recent public tremor catalog. We used PNSN API v3.0 data at 47-50 N for local dates in 2017-2025. Daytime was 08:00-18:00 and night was 20:00-06:00 in Pacific civil time. The daytime share of detections in these hours was 40.39% on weekends and 32.11% on weekdays. The difference was 8.28 percentage points. A 28-day block bootstrap gave a conditional 95% interval of 6.42 to 10.34 points. No one of 20,000 block calendar-phase draws gave as large an absolute difference. Equal weight for 1,080 active days gave a difference of 8.05 points, with limits of 4.90 to 11.29. Each annual contrast was positive. This extends earlier reports of a weekend effect; it is not its first discovery. The pattern is consistent with a time-dependent observation process but does not identify its cause. Unknown uptime, burst dependence, catalog changes and conditional block assumptions limit inference. Code, daily evidence, source hashes, simulation draws, checks and a figure are included.

Cascadia · tectonic tremor · weekend effect · detection bias · block bootstrap · calendar phase