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TitleFocal depth of earthquakes of the St. Lawrence Valley based on crustal phases recorded within 100 km epicentral distance
AuthorLamontagne, M
SourceGeological Survey of Canada, Open File 8032, 2016, 25 pages, (Open Access)
PublisherNatural Resources Canada
Documentopen file
Mediadigital; on-line
File formatpdf
NTS21L/05; 21L/11; 21L/12; 21L/13; 21L/14; 21L/15; 21L/16; 21M/02; 21M/03; 21M/04; 31I/01; 31I/02; 31I/07; 31I/08; 31I/09; 31I/10; 31I/16; 31H; 31G/01; 31G/02; 31G/07; 31G/08; 31G/09
AreaSt. Lawrence River; Gulf of St. Lawrence; Quebec City; Montreal
Lat/Long WENS -73.0000 -67.5000 49.5000 46.0000
Subjectsmarine geology; geophysics; seismic risk; seismicity; seismic zones; epicentres; earthquake risk; earthquakes; earthquake catalogues; marine environments; marine deposits; bathymetry; Charlevoix Seismic Zone; Lower St. Lawrence Seismic Zone
Illustrationslocation maps; tables; graphs
Natural Resources Canada Library - Ottawa (Earth Sciences)
ProgramWestern Canada Geohazards Project, Public Safety Geoscience
Released2016 10 06
AbstractWe have computed the focal depth of 53 earthquakes of the St. Lawrence Valley (defined as latitudes 45oN to 47oN and longitudes 70oW to 75oW) between Montreal and Quebec City using a minimum of six Pg and Sg phases from three seismograph stations or more located within 100 km of each epicentre. In addition, the epicentre had to be within the polygon defined by the seismograph stations (i.e. the azimuthal gap had to be less than 180o). Although all 607 events of the period 1980-2015 inclusively were considered, the majority of selected events were in the period 2013-2015 when the USARRAY stations occupied the region of interest. Computer scripts were written to select phases, stations and solutions that met our criteria. All resulting hypocentres locate between 10 and 21 km focal depth. Only 2 % of the 607 events had an Rg phase that suggests a focal depth of less than 5 km. Together with hypocentres computed with other methods such as the Regional Crustal Depth Determination, these new hypocentres help determine the crustal levels susceptible to fault reactivation.
Summary(Plain Language Summary, not published)
Focal depths of 53 earthquakes in the St. Lawrence valley were computed.