The Canadian Rockies and Alberta Network (CRANE): New Constraints on the Rockies and Western Canada Sedimentary Basin

Abstract

The Canadian Rockies and the neighboring Alberta Basin mark the transition from the old North American continental lithosphere (east) to young accreted "terranes" (west). Geologic, seismic, and magnetic data in this region have suggested complex crustal domains, conductive anomalies, and major seismic velocity gradients in the mantle. However, the nature of the boundaries between the basement domains and their vertical extents remains controversial due to the lack of exposed geology and limited seismic and electromagnetic receivers. Since 2006, the seismic data coverage and depth sensitivity have received a major boost from the establishment of the Canadian Rockies and Alberta Network (nicknamed CRANE), the first semi-permanent broadband seismic array in Alberta. The availability of the array data provides vital constraints on the regional micro-earthquakes and crust/mantle seismic structures. Among the broad range of ongoing efforts, this study highlights promising results from the analyses of P-to-S wave receiver functions, shear wave splitting amplitudes/directions, and ambient seismic noise. Our preliminary receiver-function stacks show that the base of the crust gradually shallows from approximately 60 km beneath the Rockies near the Canadian-U.S. border to 37-40 km beneath central Alberta; the latter range is consistent with earlier findings from active-source experiments. Converted waves from "littered" crust and/ or lithosphere have also been detected at a number of stations in the depth range of 80-130 km. Complexities in the lithosphere are further evidenced by our regional shear wave splitting measurements. We infer a strong east-west change of mantle flow pattern, consistent with present-day plate motion. The spatial distribution of the SKS fast orientations highlights the contrasting crust/mantle structures and histories between the Rockies and adjacent domains. Dynamic effects associated with a migrating continental root east of the province may be important. Finally, our preliminary inversions using ambient seismic noise indicate more than 0.8 km/s in peak-to-peak group velocity variations throughout the crust. The upper crust beneath the Alberta Basin is dominated by low Rayleigh-wave group velocities. A lower-than-expected correlation between seismic velocities and tectonic domain boundaries suggests significant tectonic overprinting in the southern Western Canada Sedimentary Basin. Overall, the broadband seismic data from CRANE could play a key role in uncovering the mysteries of the crust and mantle beneath the transition region between cratons and terranes.

Stress drop estimates and hypocenter relocations of induced seismicity near Crooked Lake, Alberta

“…In the meantime, seismic station coverage in western Canada has increased significantly in recent years [e.g., Gu et al, 2011;Novakovic and Atkinson, 2015], where additional stations were deployed for the purposes of monitoring induced earthquakes. Schultz et al [2015a] establish a temporal correlation of > 99.99% between the timing of these operations and c 2016 American Geophysical Union.…”

“…We begin with a list of 82 events (M 1.8 to M 4.6) from the NRCan Earthquake Catalogue, hereafter NRCan, from December 2013 to June 2015. We obtain waveform data from the TD, RAVEN [Schultz and Stern, 2015], CRANE [Gu et al, 2011], and CN networks (Figure 1), where the majority of the stations have a sampling rate of 100 sps while others are sampled at a rate of 40 sps. After removing instrument response and filtering from 0.5 Hz to the Nyquist frequency, we cut the raw data into four-second windows beginning 0.5 seconds before the respective P-and S-wave arrivals.…”

3-D geomechanical–numerical model of the contemporary crustal stress state in the Alberta Basin (Canada)

“…5) by directional kriging. These are data from seismic refraction studies (Bouzidi et al, 2002;Burianyk et al, 1997;Clowes et al, 2002;Fernández-Viejo and Clowes, 2003;Halchuk and Mereu, 1990;Németh et al, 1996Németh et al, , 2005Spence and McLean, 1998;Welford et al, 2001;Zelt and White, 1995) and from teleseismic studies (Gu et al, 2011;Shragge et al, 2002).…”

Sharp mantle transition from cratons to Cordillera in southwestern Canada

“…This semipermanent network [Gu et al, 2011] was designed to complement the existing stations at Leduc (EDM, Alberta), Waterton Lake (WALA, Alberta), and Sale Mountain (SLEB, British Columbia), three permanent broadband stations from the Canadian National Seismograph Network (CNSN). With average spacing of~150 km between stations, these two arrays provide semiuniform coverage beneath the southern WCSB.…”

“…function technique [Langston, 1977;Vinnik, 1977;Ammon, 1991;Ligorria and Ammon, 1999;Cassidy, 1995;Bostock, 1996;Liu et al, 2003;Tauzin et al, 2008;Gu et al, 2011;Thompson et al, 2011], with critical improvements to counteract the high noise levels caused by soft glacial sediments. The short-period nature of receiver functions computed from P-to-S converted waves enables high-resolution constraints on the depth and impedance (the product of density and velocity) contrast of crustal and mantle interfaces beneath the seismic stations (see Rondenay [2009] for review).…”