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TitleAssessing earthquake rates and b-value given spatiotemporal variation in catalog completeness: Application to Atlantic Canada
AuthorPlourde, A PORCID logo
SourceSeismica 2023 p. 1-11, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20220415
Mediapaper; digital; on-line
File formatpdf; html
AreaAtlantic Canada; Canada
SubjectsScience and Technology; general geology; seismicity; earthquakes; earthquake studies; seismic risk
ProgramMarine Geoscience for Marine Spatial Planning
Released2023 09 13
Spatiotemporal variations in the magnitude of completeness Mc make it challenging to confidently assess seismic hazard or even to simply compare earthquake rates between regions. In this study, we introduce new techniques to correct for heterogeneous Mc in a treatment of the eastern and Atlantic Canada earthquake catalog (1985--2022). We first introduce new methodology to predict Mc(x,t) based on the distribution of seismometers. Second, we introduce a modified maximum-likelihood estimator (MLE) for b (the b-value) that accounts for spatiotemporal Mc variation, allowing the inclusion of more earthquakes. Third, we compute the ratio of detected/predicted M>1 earthquakes as a function of Mc and apply it to create a calibrated M>1 event-rate map. The resulting map has advantages over a moment-rate map, which is effectively sensitive only to the very largest earthquakes in the dataset. The new MLE results in a modestly more precise b when applied to the Charlevoix Seismic Zone, and a substantial increase in precision when applied to the full Atlantic Canada region. It may prove useful in future hazard assessments, particularly of regions with highly heterogeneous Mc and relatively sparse catalogs.
Summary(Plain Language Summary, not published)
Earthquake hazard assessments, and earthquake science in general, can be complicated by the uneven distribution of the seismometers used to detect earthquakes. This study examines the earthquake catalog from eastern and Atlantic Canada (from 1985 to 2022) and introduces new methods to deal with the uneven seismometer distribution. We first analyze what magnitude of earthquake we are able to detect as a function of location and time. Second, we introduce a new way to estimate the ``b-value", which describes the ratio of large earthquakes to small earthquakes. We apply the new method to the full map region and, separately, to the Charlevoix Seismic Zone in Quebec. Finally, we produce an earthquake map that is calibrated for the historical distribution of seismometers. These methods may be useful in future earthquake hazard assessments, particularly for regions with highly-uneven seismometer coverage and low to moderate earthquake rates.

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