This GIS dataset depicts earthquakes within Alberta from September 2006 through 2017. The events were recorded on seismographs belonging to the Regional Alberta Observatory for Earthquake Studies Network (RAVEN), Canadian Rockies and Alberta Network (CRANE), the Canadian National Seismograph Network (CNSN), the Alberta Telemetered Seismograph Network (ATSN), the Montana Regional Seismograph Network (MRSN), the TransAlta Dam Monitoring Network (TD), the Northeast British Columbia Network (NEBC), and the American National Seismograph System (USRef).
The locations were calculated using the Boulder Real Time Technologies Antelope collection of software for the acquisition, archival, and analysis of seismic waveforms with the hypocentre inversion algorithm GENLOC. The locations have been reviewed and are believed to represent actual seismic events. As more seismic data or information becomes available locations may be added, modified, or removed from future versions of this dataset.
Each event in the database has its own degree of precision based on the number of observations (body phases used in the location) and the number of unknown variables to be solved for, essentially four variables (latitude, longitude, depth, and origin time) or three if depth is fixed. The precision of location is reflected in the attribute SDOBS (standard deviation of observations), defined as the square root of the sum of the squares of the residuals (between the observed arrival and the predicted arrival of a phase) divided by the number of degrees of freedom (number of observations minus the number of unknowns). The diagonal elements of the covariance matrix are given in the attribute fields SXX, SYY, SZZ, and STT. The off-diagonal elements of the covariance matrix are SXY, SXZ, SYZ, SXT, SYT, SZT and are assumed symmetric.
Events where the depth was fixed have no error values associated with SZZ, SXZ, SYZ, or SZT.
The magnitude was not calculated for some events either because the reporting seismic stations were too distant or response files were not available for the reporting stations. The magnitudes for these events were likely close to or below the magnitude threshold for that region. In these cases a magnitude of -999 was assigned.
The points represent unique seismic events determined by date, time, latitude, longitude, and depth.
The data points represent earthquakes that were capable of being located due to their size, proximity to seismic stations, and signal to noise ratio of the seismic stations. Events whose phase arrivals were not detected and picked on more than two seismic stations were not located and included in the database. Events that were judged to be surface mining blasts due to location and time of day or to blast reports from industry were not included in the earthquake database. The dataset is considered generally complete for events above a 2.5 local magnitude (ML) for most of Alberta, although it approaches a 3.0 magnitude threshold for northern Alberta prior to 2014. After 2014 the magnitude threshold is closer to 2 ML but varies throughout the province. The magnitude threshold is lower than 2.0 for the Rocky Mountain Foothills and southern Alberta. In the region near Rocky Mountain House it approaches 1.0 ML after the installation of the TD stations in 2014.
Blasts from mining activities such as known surface coal mines or limestone quarries were not included in the dataset. The criteria for determining that an event was a blast include: location at a known mine, time of event during mine operations, spectral content of event. Locations of events north of latitude 55 N and in the Peace River Arch region were more poorly constrained and therefore time of day was used as a discriminator. Some of these events labeled as blasts could have been mislabeled.
Depths are generally not well constrained. In version 1.0 for most cases the depth was fixed at 1 kilometre beneath the surface. The uncertainty for depth, given that reporting stations are generally 50 to 150 km away from the events, is at least +/- 1 kilometre. As of version 1.1 of the earthquake catalogue all depths were fixed at 0, 1, 3, 5, 10, or 15 km.
From November 2016 onwards the depths are allowed to be free variables that were calculated by the GENLOC algorithm. The depths are reported as integers. The attribute DTYPE which indicates whether the depth was fixed or a not has two values: 'g’ for those events with the depth fixed by the geophysicist and ‘f’ for events in which the depth was allowed to be a free variable.
Data acquisition: Raw seismic waveforms were acquired, using BRTT's Antelope real-time seismic acquisition software, from over eight sources: near-real time data from Earthquake Canada (EC) for the Canadian National Seismograph Network (CN:CNSN) and the Northeast British Columbia Network (CN:NEBC) using the Antelope program orb2orb; near-real time data transfers from Incorporated Research Institutes for Seismology (IRIS) for the Montana Regional Seismograph Network (MB:MRSN), the American Advanced National Seismic System (US:ANSS), the Regional Alberta Observatory for Earthquake Studies Network (RV:RAVEN), The Alberta Telemetered Seismograph Network (RV:ATSN), the TransAlta Dam Monitoring Network (TD), and one station from the Canadian Rockies and Alberta Network (Y5:CRANE) using the Antelope program slink2orb. For earlier versions of the catalogue offline raw data was collected from the Canadian Rockies and Alberta Network (Y5: CRANE) biannually from compact flash cards in station dataloggers. The CRANE data was converted to the Standard for the Exchange of Earthquake Data (SEED) format and merged with the real-time data for the years 2006 through 2012. From 2013 onwards, only waveforms from telemetered stations are routinely used for near real-time analysis of events that are included in the catalogue. For one event on December 16, 2017 at 11:29:06 (UTC), however, the location and magnitude were re-calculated with additional waveform data provided by Industry.
Data processing: batch processing of the waveform data was performed with the Antelope dbdetect module to detect seismic signals in the raw data, dbgrassoc module to associate detections into seismic events with phase arrivals flagged, and the dbpick or smartpick modules were used to perform visual scans and manually pick phase arrivals for missed events.
Data analysis: The phase arrivals were imported into the dbloc2 module. The placement of picks were refined, then using the GENLOC hypocentre inversion algorithm to produce earthquake locations giving the latitude, longitude, depth, date, and time in Universal Co-ordinated Time (UTC). The dbevproc module was used to measure and calculate local magnitudes (ML).
GIS shapefile creation: The solutions containing the latitude, longitude, depth, date and time of origin, and magnitude of each earthquake were stored in an Antelope relational database. The database of earthquake locations was transferred to a comma-separated values (CSV) file using the db2xml program. The CSV files were converted to shapefiles using ArcGIS.
The existing database is rechecked for accuracy during annual revisions. Depths for all events prior to November 2016 were fixed at 0, 1, 3, 5, 10, or 15 km beneath the surface. From November 2016 onwards event depths were not routinely fixed. Events that were verified as earthquakes were retained. Events that were not verified and judged to be either mining blasts or more than 10 km outside the provincial boundaries of Alberta were reclassified and are not part of the dataset.
Several fields were removed from version 1.0 (the first installment), these include EVID, ORID, ETYPE, ALGO. The field EVNAME was renamed LOCATION.
One event was removed from 2011 that occurred near Cardston, AB. Its removal was due to a poor location, in that the arrivals were too small to be detected on the nearest stations (e.g., RAYA, WALA, and PRDA), but were picked up on farther short period instruments in Montana. The magnitude was in error (reported as 3.89) due to incorrect gain in the response files for the Montana stations and was more likely less than a 1.0 ML.
In the years prior to 2013 the velocity model used for locations was a two layer 1D model (cn01) created and used by the Pacific Geoscience Centre for earthquakes in Western Canada. Events for 2013 and later are calculated using in-house regional models for the regions around Fox Creek, Brazeau River, Rocky Mountain House, and Cardston. These models have three or more layers. Cn01 is still used for events in the Rocky Mountain Foothills and outside the above areas.
Updated in March 2016 to include events from 2012 and 2015.
Updated in March 2017 to include events from 2016.
Updated in March 2018 to include events from 2017.