Changing magnitude-type weights account for most of a larger-event share drop in a 2020 Puerto Rico catalog sample
We tested how a change in catalog magnitude types affects an observed change in earthquake size. We used a fixed USGS snapshot for Puerto Rico, within 50 km of a fixed center, on days 1-7 and 7-30 after 7 January 2020. Among local and duration magnitude records at magnitude 3 or more, the share at 3.5 or more fell from 47.50% to 28.12%. A symmetric two-part calculation assigned 15.71 percentage points of this 19.38-point drop to changes in type weights. It assigned 3.67 points to changes within types. Conditional 95% two-day block intervals were -20.91 to -10.15 points for the type-weight term and -11.59 to 2.97 points for the within-type term. The type-weight term had the same sign at two other cutoffs and at a 100 km radius. This is an arithmetic result for selected catalog records. Type choice can depend on event size and detection. Thus the result does not prove a measurement error or rule out a physical change. The study adds a type-weight check to a prior campaign forecast test. Code, raw data, event rows, resample values, and an independent arithmetic check are included.
Puerto Rico · aftershocks · magnitude types · catalog composition · standardization · ComCat
References
5- usesThe forecast gain from a second decay term depended on exponent settings in Puerto Rico on days 7-30 at magnitude 3 or more sci:sha256:c4e5b97e90080abf8f56a862c786a199e2bd09a7463679fd6194385d31f47fce
We reuse its shared raw snapshot and time and radius settings. It reported the magnitude-type shift. We add a new arithmetic decomposition and block resamples.
- reviewsdoi:10.1785/0220210222
Prior public aftershock forecast study reports changes in the magnitude distribution and fitted parameters. We used its public USGS abstract.
- reviewsdoi:10.1785/0120220229
The public abstract describes the complex fault network and a much denser catalog. We do not use that enhanced catalog.
- https://www.usgs.gov/programs/earthquake-hazards/magnitude-types
USGS definitions distinguish local and duration magnitudes.
- useshttps://earthquake.usgs.gov/fdsnws/event/1/query?format=csv&starttime=2020-01-07T08%3A24%3A26&endtime=2020-02-06T08%3A24%3A26&latitude=17.916&longitude=-66.813&maxradiuskm=100&minmagnitude=2.5&eventtype=earthquake&orderby=time-asc&limit=20000
Exact USGS query for the saved catalog snapshot.
Cited by
4 publicationsPublic catalog entries on Sciscape.
- usesOne added early event made a Puerto Rico spatial spread increase uncertain at M3 or more on days 1-30 in 2020
We read its magnitude mixture study. It motivates separate ML and MD checks.
- usesMean depth change was uncertain for M3+ Puerto Rico records on days 1-30 in 2020 and depended on depth-label selection
Prior campaign study supplied context on magnitude-type weights and the fixed sample.
- usesSix-hour controls reduced a short-gap spatial excess in a 2020 Puerto Rico earthquake catalog sample
Prior magnitude-type result motivated the within-type shuffle control. Data overlap; this is not independent replication.
- usesThe day-night small-event share difference was uncertain in a January-February 2020 Puerto Rico catalog sample
This published study supplied the shared raw snapshot and showed a magnitude-type shift. We test a new time-of-day contrast. The observations overlap.