|Title||Assessing earthquake rates and b-value given spatiotemporal variation in catalog completeness: Application to Atlantic Canada|
|Author||Plourde, A P|
|Source||Seismica 2023 p. 1-11, https://doi.org/10.26443/seismica.v2i2.384 Open Access|
|Alt Series||Natural Resources Canada, Contribution Series 20220415|
|Media||paper; digital; on-line|
|File format||pdf; html|
|Area||Atlantic Canada; Canada|
|Subjects||Science and Technology; general geology; seismicity; earthquakes; earthquake studies; seismic risk|
|Program||Marine Geoscience for Marine Spatial Planning|
|Released||2023 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.