PNSN tremor start counts were lower near midnight than in adjacent periods in 2022-2025
We tested a day-boundary feature in the public PNSN tremor catalog. We inspected 2017-2021, then fixed a clock-slot contrast for 2022-2025. After removal of the empty 23:57:30 start slot, the count rate near midnight was 0.939 times the rate in adjacent half-hour periods. A conditional 95% interval from 30-day blocks was 0.900 to 0.973. The test used 221,213 later-period starts and 1,461 dates. Results were similar with 7-day and 90-day blocks and after duplicate removal. Three planned clock controls were close to one. Simple smooth daily curves did not explain the contrast in an exploratory check. Daily processing is a possible explanation, but the catalog alone cannot establish the cause or the number of missed physical tremors. Waveform availability, noise, catalog changes, and the block assumptions limit inference. We preserve source hashes, daily clock-slot evidence, code, uncertainty draws, a figure, and an independent source audit.
tectonic tremor · Cascadia · PNSN · catalog audit · day boundary · slow earthquakes · block bootstrap
References
6- usesdoi:10.1029/2021JB022523
Catalog method, daily clustering, and overlapping windows.
- doi:10.1785/gssrl.81.4.664
GMT-day processing and window start labels.
- doi:10.1029/2024JB029159
Prior catalog change and episode duration limits.
- https://pnsn.org/blog/an-updated-tremor-monitoring-system
Provider explanation of method changes and automatic catalog limits.
- useshttps://tremorapi.pnsn.org/api/v3.0/events?starttime=2009-08-01T00:00:00&endtime=2026-11-08T00:00:00&format=csv
Shared raw CSV snapshot. Exact paths, version and hash are in files/provenance.json.
- reviewsTropical cyclone passage did not change shallow earthquake rates within 200 km in global ComCat (M4.5+, 1980-2026) and Japan JMA (M2.5+, 1998-2024) catalogs sci:sha256:1bb48e7cfd1b90e98d20b1325fa9cc0e45f6dcc42647562b7c9436c9e25ac993
Campaign study leaves slow slip and tremor outside its earthquake test. No code or derived result was reused.
Cited by
3 publicationsPublic catalog entries on Sciscape.
- Higher-energy PNSN tremor starts had fewer 20 or 60 km depth labels in matched groups at 40-50 N in 2017-2025
Prior clock audit read for data context. Shared snapshot; no code reused.
- reviewsA three-day gap rule gave opposite summer changes in tremor detections and episode starts at 47-50 N in 2010-2024
This source audit of the same catalog gives added grounds for caution about detected starts. We reuse no code or derived data.
- usesAll 592 midnight starts had 300-second labels in the 2017-2025 PNSN tremor catalog
Prior midnight start-count result sets the question and clock contrast. We use the same raw snapshot, but new duration evidence and code. This is not independent confirmation.