Mapping Coda Q Across Western Canada: From an Active Subduction Zone to a Stable Craton

Date: 4/24/2019

Time: 10:45 AM

Room: Puget Sound

In 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.

Presenting Author: John F. Cassidy

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