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TitleCoda Q determination across Western Canada: from a region of active subduction to a stable craton
AuthorFarahbod, A; Cassidy, J FORCID logo
SourceCanadian Geophysical Union Annual Meeting, abstract volume; 2017, 1 pages
Alt SeriesEarth Sciences Sector, Contribution Series 20170049
PublisherCanadian Geophysical Union (Vancouver, Canada)
MeetingCanadian Geophysical Union Annual Meeting; Vancouver; CA; May 29-31, 2017
ProvinceBritish Columbia
Areawestern North America; United States of America
Subjectstectonics; earthquake studies; earthquakes; subduction zones; seismicity; lithosphere; deformation; modelling; array seismology; crustal studies
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2017 01 01
AbstractIn this study we investigate the spatial variation in coda-wave attenuation (QC) across western Canada, covering a wide range of tectonic settings - from a seismically active subduction zone in the west, through a volcanic belt, to the stable craton of North America - a region of slow lithospheric deformation in the east. Our dataset is made up of more than 2500 earthquakes recorded at 85 Canadian seismic stations across the region. We employ the single back scattering approximation with a range of ellipse parameter (a2) from 20 km to 100 km. We find a very clear attenuation pattern across the study area. The lowest Q0 (Q at 1 HZ) values (e.g., Q0 of 39, a2=33 km) are in the vicinity of Nazko Cone in the Anahim volcanic Belt (AVB), the highest Q0 values (e.g., Q0 of 165, a2=90 km) are on the stable craton, and intermediate values of Q0 are determined across the Cascadia subduction zone. Our results showing low Q0 throughout the AVB provides additional support for an interpretation of magma injection into the lower crust during the 2007 Nazko earthquake swarm, fracturing of the crust, and resulting high seismic attenuation. Also, low Q0 estimates in the Horn River basin and Montney Basin can be partially attributed to Hydraulic fracture related seismicity. Within the subduction zone, Q0 is lowest closest to the active faults off the coast and in the vicinity of the only known large crustal earthquakes (1918, M~7 and 1946, M~7.3) on Vancouver Island, and Q0 increases moving inland. The highest Q0 values we determine are in the regions of slow lithospheric deformation.
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.

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