The tectonic earthquake data are primarily from a Uniform Moment Magnitude Earthquake Catalog developed for Utah and its surrounding region by Arabasz and others (2016) for the time period 1850 through September 2012. For the map, we extended the catalog through December 2016 and expanded it to include earthquakes smaller than magnitude 2.9. MIS was excluded from the compilation of Arabasz and others (2016) but has been added to the map to show its significance in east-central Utah.

Data for the seismic events plotted on the map are listed in two separate catalogs in the form of an ArcGIS feature class within a file geodatabase. The catalog files are available in the Utah Geospatial Resource Center (UGRC) State Geographic Information Database (SGID, https://gis.utah.gov/data/geoscience/) and at https://ugspub.nr.utah.gov/publications/open_file_reports/ofr-667/ofr-667.zip. The primary catalog used for the map, termed the Earthquake Catalog (EQ Catalog, Utah_EQcat_1850_2016), comprises tectonic earthquakes located within the “Utah Region” (lat. 36.75° to 42.50° N, long. 108.75° to 114.25° W) from 1850 through 2016. This region is the standard region used by the University of Utah Seismograph Stations (UUSS) for the compilation and reporting of earthquakes within and surrounding Utah. Note that the map covers most, but not all, of the Utah Region.

The map delineates two areas in east-central Utah that are characterized by predominantly (more than 90%) MIS. All seismic events (including both MIS and tectonic earthquakes) located in these two areas are listed in a separate catalog, termed the Coal-Mining-Region Catalog (CMR Catalog)(Utah_CMRcat_1928_2016), which extends from 1928 (the year of the first located event) through 2016. The EQ and CMR catalogs are mutually exclusive. The EQ Catalog does not include tectonic earthquakes located within the two delineated areas of predominantly MIS.

More information about the earthquake epicenter data is contained in UGS OFR 667 (https://ugspub.nr.utah.gov/publications/open_file_reports/ofr-667/ofr-667.pdf).