Current deformation in the northern Canadian Cordillera inferred from GPS measurements

Abstract

Continuous and campaign‐style Global Positioning System (GPS) measurements provide new constraints on the first‐order current deformation pattern of the northern Cordillera of NW Canada and eastern Alaska. The Yakutat block is currently colliding with North America in the corner of the Gulf of Alaska. Our data infer that relative Yakutat–North America motion is accommodated across the eastern boundary by right‐lateral motion (∼40 mm/a), mainly on the Fairweather fault, and minor shortening (∼6 mm/a). To the north, collision is taken up by shortening (∼31 mm/a) mainly on the Chugach–St. Elias fault system, with westward extrusion and possible counterclockwise rotation of the Yakutat block and Alaskan fore arc facilitated by ∼23 mm/a right‐lateral motion that is shared by several faults. The seismicity pattern indicates that plate boundary deformation is far reaching, producing strain throughout eastern Alaska, Yukon, and western Northwest Territories. Our GPS data confirm the transfer of strain from the Yakutat collision zone and enable the extent of plate boundary deformation to be mapped, thereby defining the western edge of “stable” North America. GPS sites in SW Yukon show motion of 3–10 mm/a to the NE, confirming that strain is transferred at least 400 km from the Yakutat collision. Continued transfer north toward the Mackenzie Delta and NE to the Mackenzie Mountains, indicated by current seismicity, is not yet well resolved by the campaign GPS data, which are hampered by coseismic and postseismic effects of the 2002 Mw 7.9 earthquake on the Denali fault in eastern Alaska.

Tectonics, climate, and mountain topography

“…[83] McKenzie Mountains (Canada) (MKM): From sparse continuously recording GPS measurements at sites SW of the mountains, Leonard et al [2007] reported a rate of convergence between them and North America of 3-10 mm/a, little different from $5 mm/yr given by Mazzotti and Hyndman [2002]. The wide range of possible rates derives in part from inconsistent velocities of campaign-style GPS measurements.…”

“…Using seismic moments of moderate earthquakes, Leonard et al [2008] inferred rates of 1.8 to 4.0 mm/yr. Recognizing the large uncertainties associated with such estimates, we use a rate at the low end of what Leonard et al [2007] suggested: 5 AE 2 mm/yr.…”

Seismic hazard in western Canada from GPS strain rates versus earthquake catalog

“…Data time spans vary from 1992 to 2008, with an average time series length of 5-6 years. Details of the regional network processing are given in Mazzotti et al [2003b] and Leonard et al [2007]. The various networks are combined, aligned to the International Terrestrial Reference Frame ITRF2000, and referenced to stable North America using the North America/ITRF2000 rigid rotation [cf.…”

“…It comprises 179 horizontal velocity vectors derived from 89 continuous and 90 campaign GPS stations throughout Alberta, British Columbia, and northern Washington [Henton et al, 2006;Leonard et al, 2007;Mazzotti et al, 2003aMazzotti et al, , 2003b] (see auxiliary material). Data time spans vary from 1992 to 2008, with an average time series length of 5-6 years.…”

EON-ROSE and the Canadian Cordillera Array – Building Bridges to Span Earth System Science in Canada

“…3). This oblique collision appears to be transferring strain to the north and northeast, causing active deformation across the Richardson and Mackenzie mountains (Mazzotti and Hyndman 2002;Leonard et al 2007;Leonard et al 2008). One intriguing question is to what extent the strain transfer occurs diffusely across hundreds of kilometres, as opposed to being accommodated by rigid blocks and a few discrete faults.…”