Earthquake Catalog Processing and Swarm Identification for the Pacific Northwest

The Pacific Northwest (PNW) of North America encompasses diverse tectonic settings that can produce damaging earthquakes near population centers. Seismicity in this region is often clustered into aftershock sequences and swarms, and their patterns and frequencies differ across subregions or tectonic regimes. Characterizing the seismicity of the PNW requires a catalog of observed earthquakes. Furthermore, applications with the catalog may require earthquake clusters to be identified and regarded separately. Unlike previous studies, we explicate how to overcome challenges when combining catalogs from different countries, particularly in accounting for duplicate events and other discrepancies. We apply this to merge authoritative catalogs for the United States and Canadian portions of the PNW, along with a third dataset with data quality measures. We also perform a window‐based search for earthquake clusters, which then get labeled as possible or definite swarms or aftershock sequences. We further split the catalog into its two primary tectonic regimes. We then study the PNW catalog’s completeness, and the extent to which this varies between the northern and southern parts of the region. We provide a harmonized international PNW catalog with derived variables describing earthquake clustering and tectonic regimes. This entire processing pipeline has also been fully documented and is supported with software, enabling its use in other seismic regions.