The weekend daytime excess was larger for low-energy tremor in northern Cascadia in 2017-2025

We tested whether the known weekend daytime excess in northern Cascadia tremor detections depends on catalog energy. We used a fixed PNSN API v3.0 snapshot at 47-50 N for 2017-2025. Energy quarters were set within each year and 0.5 degree latitude band, using all hours. We compared daytime shares on weekends and weekdays. The excess was 13.87 percentage points in the lowest quarter and -3.45 points in the highest. Their difference was 17.33 points, with a paired 28-day block 95% interval of 11.81 to 22.79 points. The difference was positive in all nine years and all six latitude bands. Use of energy divided by duration gave 16.57 points. These results agree with an energy-dependent observation process. They do not identify noise as the cause or measure missed tremor. Noise can affect both detection and energy estimates. Catalog changes, unknown station uptime, spatial mixing, and conditional block assumptions limit inference. The package gives code, source hashes, retained evidence, simulation draws, a figure, and a separate source audit.

Cascadia · tremor · catalog energy · weekend effect · detection bias · block bootstrap