Characterization of the southern Rocky Mountain Trench near Valemount, British Columbia, using receiver functions
Date
2020-05-21
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Abstract
The Rocky Mountain Trench (RMT) within the eastern Canadian Cordillera marks a prominent topographic and physiographic boundary within the exotic terrains that accreted onto the North American continent. Previous geophysical data have shown that the RMT coincides with a ∼10 - 15 km decrease in crustal and lithospheric thickness from east to west. Receiver function (RF) analysis is a suitable method for investigating the RMT because it provides estimates of the depths of lithospheric boundaries. A deployment of ten broadband seismometers between July 2017 and July 2019 within the RMT near Valemount, B. C., recorded over 300 teleseismic earthquakes with magnitudes greater than 5.5 at epicentral distances between 30◦ and 100◦ degrees. Due to high levels of cultural noise in the region, removing low signal-to-noise ratio events left between 57 and 17 events per station to use for further analysis. Assuming average crustal velocities, stacks of low frequency RFs show a high-amplitude positive arrival at depths greater than 45 km. When viewed at higher frequencies, these RFs reveal arrivals at depths between 20-30 km. These RFs are analyzed through joint inversions with a surface wave dispersion curve, common conversion point stacking, and H-k stacking. There are three major findings of this study: (1) The Moho near the RMT around Valemount is relatively deep (> 45 km) and the crust is thicker to the south, interpreted to indicate that this location marks the northern most segment of the portion of the southwestern Canadian Cordillera where the crust underwent a greater amount of shortening and thickening compared to the rest of the Cordillera. (2) Strong midcrustal discontinuities are present in the RF stacks, and they are interpreted to mark the depth of the Rocky Mountain basal detachment, corresponding to the interface between the North American basement and accreted terranes. (3) The RF signals vary strongly with back-azimuth, likely resulting from a combination of crustal heterogeneity, anisotropy, and dipping layers.
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Rocky Mountain Trench, Receiver Function
Citation
Coffey, J. R. (2020). Characterization of the southern Rocky Mountain Trench near Valemount, British Columbia, using receiver functions (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.