ALBERT

Description: Canada has four of the 20 largest water reservoirs in the world, with 16 that are at least 75 m deep and have a volume greater than 109  m3. Eleven of these are located in the Canadian Shield of Quebec, and five are located in the Cordillera of British Columbia and Alberta. Six of these large reservoirs, along with two other smaller reservoirs, have been associated with reservoir‐triggered seismicity (RTS). The proportion of reservoirs with an RTS that is larger than Nuttli magnitude MN 3.0 (25%; i.e., four cases) is similar to the one for worldwide counterparts (22%). All RTS cases are located in the Canadian Shield of Quebec, which is an area that is weakly seismically active. RTS is of a small magnitude (the largest event was magnitude MN 4.1). Based on the known cases of RTS and those that had no associated seismicity, there are a few conclusions that can be drawn. Before the mid 1970s, many potential triggered earthquakes could have been below the detection threshold that was offered by the Canadian National Seismograph Network (CNSN) at the time (generally magnitude 3.5). The weight of the reservoirs does not appear to be the main factor that triggers RTS; two of the reservoirs with the largest volumes do not have any associated activity. In all RTS cases, it is almost impossible to relate the activity to specific fault characteristics. In some RTS cases, filling was not completed when the RTS started. For these cases, it is not easy to distinguish between a rapid response (such as the weight of the reservoir increasing the pore‐fluid pressures at depth) and the delayed type of response, in which the pore‐fluid pressure diffusion leads to reactivation of the fault. For the majority of RTS cases, however, a delayed‐response type appears more likely; that is, it is more likely that activity that is started shortly after the initial impoundment will continue for many months, sometimes in swarms, and finally stop after a few years.

Description: Slipstream Slump, a well-preserved 3 km wide sedimentary failure from the frontal ridge of the Cascadia accretionary wedge 85 km off Vancouver Island, Canada, was sampled during Canadian Coast Guard Ship (CCGS) John P. Tully cruise 2008007PGC along a transect of five piston cores. Shipboard sediment analysis and physical property logging revealed 12 turbidites interbedded with thick hemipelagic sediments overlying the slumped glacial diamict. Despite the different sedimentary setting, atop the abyssal plain fan, this record is similar in number and age to the sequence of turbidites sampled farther to the south from channel systems along the Cascadia Subduction Zone, with no extra turbidites present in this local record. Given the regional physiographic and tectonic setting, megathrust earthquake shaking is the most likely trigger for both the initial slumping and subsequent turbidity currents, with sediments sourced exclusively from the exposed slump face of the frontal ridge. Planktonic foraminifera picked from the resedimented diamict of the underlying main slump have a disordered cluster of 14C ages between 12.8 and 14.5 ka BP. For the post-slump stratigraphy, an event-free depth scale is defined by removing the turbidite sediment intervals and using the hemipelagic sediments. Nine 14C dates from the most foraminifera-rich intervals define a nearly constant hemipelagic sedimentation rate of 0.021 cm/year. The combined age model is defined using only planktonic foraminiferal dates and Bayesian analysis with a Poisson-process sedimentation model. The age model of ongoing hemipelagic sedimentation is strengthened by physical property correlations from Slipstream events to the turbidites for the Barkley Canyon site 40 km south. Additional modelling addressed the possibilities of seabed erosion or loss and basal erosion beneath turbidites. Neither of these approaches achieves a modern seabed age when applying the commonly used regional marine 14C reservoir age of 800 years (marine reservoir correction ΔR = 400 years). Rather, the top of the core appears to be 400 years in the future. A younger marine reservoir age of 400 years (ΔR = 0 years) brings the top to the present and produces better correlations with the nearby Effingham Inlet paleo-earthquake chronology based only on terrestrial carbon requiring no reservoir correction. The high-resolution dating and facies analysis of Slipstream Slump in this isolated slope basin setting demonstrates that this is also a useful type of sedimentary target for sampling the paleoseismic record in addition to the more studied turbidites from submarine canyon and channel systems. The first 10 turbidites at Slipstream Slump were deposited between 10.8 and 6.6 ka BP, after which the system became sediment starved and only two more turbidites were deposited. The recurrence interval for the inferred frequent early Holocene megathrust earthquakes is 460 ± 140 years, compatible with other estimates of paleoseismic megathrust earthquake occurrence rates along the subduction zone.

Description: At 8:04 P.M. Pacific daylight time (PDT) on 27 October 2012 (03:04 universal time (UT), 28 October), Canada's second largest instrumentally recorded earthquake rocked Haida Gwaii (formerly Queen Charlotte Islands) and the mainland coast of British Columbia. The M 7.7 event off the west coast of Moresby Island caused a tsunami with local runup of more than 7 meters and amplitudes up to 0.8 meter on tide gauges 4000 kilometers away in Hawaii. Shaking was felt as far away as the Yukon, Alberta, Washington, and Montana, up to 1500 kilometers away. Little damage was caused, as the immediate region is an uninhabited National Park Reserve. The closest point of the rupture zone, as defined by aftershocks (Figures 1a and 1c), was 50 kilometers from the nearest community, Queen Charlotte, where damage was confined to a few chimneys and slumped roads.