The day-night small-event share difference was uncertain in a January-February 2020 Puerto Rico catalog sample

We tested whether the share of small earthquakes differs between local day and night in a fixed USGS catalog. We used 28 complete local dates from 9 January to 5 February 2020, within 50 km of a fixed center. The sample has 1641 local and duration magnitude records at magnitude 2.5 or more. Small means magnitude below 3.0. Day means 06:00 to 18:00 at UTC-4. The adjusted daytime share was 2.80 percentage points lower than the nighttime share after controls for date and magnitude type. A conditional 95% two-day block interval was -9.20 to 5.05 points. A daily random phase test gave a two-sided probability of 0.42285. All tested block intervals included zero. These data do not establish a day-night difference or its absence. The short revised catalog, unknown detection threshold, event dependence and conditional uncertainty limit inference. Code, fixed inputs, all primary simulation statistics and an independent calculation are included.

Puerto Rico · aftershocks · diurnal variation · catalog completeness · null result · magnitude types