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TitleSeismic attenuation in the interior of British Columbia and westernmost continental craton
AuthorFarahbod, A M; Cassidy, J F
SourceGeological Survey of Canada, Open File 8221, 2018, 69 pages,
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
File formatpdf
ProvinceBritish Columbia
NTS82E; 82F; 82G; 82H; 82J; 82K; 82L; 82M; 82N; 83C; 83D; 83E; 92; 93; 94; 102; 103; 104; 114
Lat/Long WENS-141.0000 -112.0000 60.0000 48.0000
Subjectsgeophysics; tectonics; fossil fuels; seismology; seismicity; seismic risk; earthquakes; earthquake magnitudes; earthquake foci; epicentres; seismic waves; attenuation; tectonic setting; crustal studies; continental crust; petroleum resources; hydrocarbon recovery; hydraulic fracturing; Canadian Cordillera; Canadian National Seismic Network; Foreland Belt; Omineca Belt; Intermontane Belt; Coast Belt; Insular Belt; Anahim Volcanic Belt; Stikinia; North American Craton; Horn River Basin; Montney Basin; Ancestral North America; coda waves; geological hazards; Phanerozoic; Precambrian
Illustrationslocation maps; geoscientific sketch maps; seismograms; plots; tables
ProgramAssessing Earthquake Geohazards, Public Safety Geoscience
ProgramPOLARIS - Portable Observatories for Lithospheric Analysis and Research Investigating Seismicity
ProgramCanadian Hazard Information Service
Released2018 02 22
AbstractIn this study we investigated coda-wave attenuation (QC) in the interior of British Columbia, with a focus on stations in the eastern Cordillera and westernmost continental craton using records from 13 stations (short period and broadband) of the Canadian National Seismic Network (CNSN). Our dataset is comprised of 1832 earthquakes recorded between 1992 and 2017 with magnitudes ranging from 1.5 to 4.9, depths from 0 to 54 km (with the vast majority being <15 km) and epicentral distances of 15 to 100 km. This gives a total of 1214 high signal-to-noise (S/N) traces (S/N?5.0) useful for QC calculation (with a range of ellipse parameter, a2, of 20 to 100) across the region. Coda windows were selected to start at tc = 2tS (two times the travel time of the direct S wave), and were filtered at center frequencies of 2, 4, 8, 12 and 16 Hz. Our study reveals a consistent pattern. We find that in the interior of BC, the lowest Q0 values (e.g., Q0 of 45) are at station BCBC at the western end of the Anahim Volcanic Belt. This is consistent with previous studies showing a low average Q0 of 53 (a2 of 30-50 km) for stations within that volcanic belt. The highest Q0 values that we find (e.g., Q0 of 165) are at station BLBC, located on the western edge of the continental craton. Other stations in the interior of BC show intermediate values of Q0. One surprising result is that FNBB and BMBC stations in northeast BC - also located on the western edge of the continental craton - show consistently low Q0 values (46-76 over the range of a2 from 20 to 70). Those stations were deployed in a region of hydraulic fracturing activity, and the low Q0 values may be partially attributed to fluids or fracturing in the uppermost crust.
Summary(Plain Language Summary, not published)
This study examines seismic attenuation across western Canada in a wide range of tectonic environments - from an active subduction zone in the west, through a volcanic belt, to the stable craton in the east. We determine a clear link between the attenuation patterns, the tectonic setting, and the seismicity rate - with the greatest attenuation in the most seismically active regions, and the lowest attenuation on the stable craton. Our research helps to constrain the boundaries of various tectonic environments across western Canada, and provides new details on the seismic attenuation - both of which will contribute to improved earthquake and volcanic hazard models for this region.