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TitleTemporal variations in coda Q before and after the 2017 Barrow Strait earthquake (Mw 5.9) in Nunavut and the 2012 Haida Gwaii earthquake (Mw 7.8) in British Columbia
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorFarahbod, A M; Cassidy, J FORCID logo
SourceGeological Survey of Canada, Open File 8930, 2022, 67 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediadigital; on-line
File formatpdf
ProvinceNunavut; British Columbia
NTS103B; 103C; 103F; 103G; 58F; 58G; 68E/01; 68H/01; 68E/02; 68E/07; 68E/08; 68E/09; 68E/10; 68E/15; 68E/16; 68H/02; 68H/07; 68H/08; 68H/09; 68H/10; 68H/15; 68H/16
AreaHaida Gwaii; Barrow Strait
Lat/Long WENS-134.0000 -130.0000 54.0000 52.0000
Lat/Long WENS -98.0000 -92.0000 76.0000 74.0000
Subjectstectonics; mathematical and computational geology; earthquakes; earthquake studies; seismicity; seismology
Illustrationslocation maps; seismic images; seismic profiles; tables
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2022 11 21
AbstractIn this study, we examine potential temporal changes in coda Q values for two significant Canadian earthquakes in different tectonic environments: the 2017 (Mw 5.9) Barrow Strait earthquake along Canada's northern margin and the 2012 (Mw 7.8) Haida Gwaii subduction earthquake on Canada's west coast. Waveforms from 124 earthquakes (2.0 <= M <= 4.6) for ~30 years prior to the January 8, 2017 Barrow Strait earthquake and 66 events (mainly aftershocks of M 2.0-5.3) in about 4 years after the mainshock recorded by the closest seismic station (RES) of the Canadian National Seismograph Network (CNSN) were utilized in this study. Based on our analysis, overall average of Q0 (Q at 1 Hz) decreased from 92 (before the mainshock) to 81. The most significant decrease in the frequency range between 2 and 16 Hz is observed for areas corresponding to ellipse parameter a2 of 50, 70 and 80 mainly related to aftershock activity. Precursory Q changes could not be evaluated before the mainshock due to the lack of reported seismicity within 100 km of the recording seismic station for almost 2 years from April 2015 to January 2017. Coda Q values before and after the October 28, 2012 Haida Gwaii earthquake in British Columbia show a similar pattern. Waveforms from 249 earthquakes (2.0 <= M <= 4.9) in 2 years before the mainshock and 498 events (2.5 <= M <= 6.3) in 2 years after the mainshock recorded by the three closest seismic stations of the CNSN were utilized. Overall average of Q0 decreased from 89 (before the mainshock) to 69 (station BNB), from 90 to 79 (station DIB) and from 86 to 78 (station VIB). In general, these results are in agreement with other global studies that show a decrease in Q0 following a major earthquake, likely the result of increased fracturing and fluids in the epicentral region.
Summary(Plain Language Summary, not published)
This is the first known study to look at the attenuation of seismic waves in different tectonic environments of Canada, and how the attenuation changes before and after significant earthquakes. We find that following both the M5.9 Barrow Strait, NU earthquake and the M7.8 Haida Gwaii, BC earthquake, attenuation increased - especially at stations closest to the earthquake. This is likely caused by increased fracturing of rock and fluids in the vicinity of the fault zone.

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