Western British Columbia Research Articles

Projected seasonal flooding in Canada under climate change with statistical and machine learning

Study regionCanada Study focusFloods are among the costliest and deadliest natural hazards in the world. To date, little is known about future seasonal flooding across all Canada. In this paper, data-driven models for flood occurrence (i.e., happening of a flood) and impact (i.e., displaced population) were calibrated for spring and summer seasons in 14,000 watersheds across Canada. Generalized Additive Models (GAM), Random Forests (RF) and Gradient Boosting Machines (GBM) were considered to model seasonal floods. The best-performing flood models were then used with regional climate models to assess the effect of climate change on flooding for three time horizons: historical, medium-term (∼2050) and long-term (∼2080). New hydrological insights for the regionGAM offered the best out-of-sample performance trade-off in both seasons for predicting flooding in Canada. Projections with GAM showed a general increase in summer flooding occurrence and impact in 2050 and 2080, mainly in the Yukon, western British Columbia, southern Prairies, Ontario and Quebec and some Atlantic provinces. Results for spring flooding were more mixed, but there seemed to be a slight decrease in the impact of spring flooding in the southern Prairies, particularly in 2080. The combination of statistical/machine learning and climate models have provided a more detailed and contrasted picture of the projected seasonal flooding situation over Canada that will help authorities better mitigate future flood risks.

Seismicity at the intersection of the Coast Shear Zone and Anahim Volcanic Belt near Bella Coola, British Columbia, Canada

In the Coast Mountains of western British Columbia, an anomalous seismicity concentration exists near the intersection of the Coast Shear Zone, a major northwest–southeast trending Eocene-age shear zone that accommodated deformation between the Pacific and North America plates, with the Anahim Volcanic Belt, an east-northeast–west-northwest trending zone of volcanic features that decrease in age to the east. To better characterize seismicity in the Coast Mountains, we augment the existing Natural Resources Canada seismicity catalogue by applying an automatic detection and location algorithm to both permanent Canadian National Seismic Network stations and temporary stations from the 2005–2006 BATHOLITHS deployment, resulting in 837 relocated events with at least three paired P- and S-phase picks. Double-difference relocation reveals several small-scale linear strands subparallel to the Coast Shear Zone and within the Anahim Volcanic Belt and three clusters of events striking at a high angle to the Coast Shear Zone that occurred as swarms in 2015 and 2017. First-motion focal mechanisms exhibit extensional and strike-slip faulting. Our observations indicate that most of these events are not associated with surficial processes such as landslides, but rather, we hypothesize that the interaction of the Anahim Volcanic Belt and Coast Shear Zone has weakened the lithosphere in this region, leading to current-day strain localization and high heat flow that manifest seismicity, including swarm-like activity.

Improved Provenance Constraints for Nanaimo Group Sediments, British Columbia, Canada, Through Zircon LA‐ICP‐MS Depth‐Profiling

AbstractDetrital zircon from Late Cretaceous rocks of the Insular Superterrane have become an important constraint on Cordilleran paleogeography. These interpretations are largely based on the occurrence of a unique detrital zircon facies characterized by a broad Paleoproterozoic (mode 1.70 Ga) and narrow Mesoproterozoic mode (1.38 Ga) in Cordilleran sedimentary rocks. However, uncertainty about the provenance of this facies and the broad geographic distribution of rocks in which it is found limits its usefulness in constraining paleogeography. Detrital rims found on Mesozoic, Proterozoic, and Archean‐aged zircon cores from the Late Cretaceous Nanaimo Group of Western British Columbia, Canada provide constraints into its provenance. Depth‐profiling of a large population of grains (N = 16; n = 3,000), combined with observations regarding zircon external morphology, internal growth textures, U/Th ratios, and U concentrations, indicate high‐grade metamorphism occurred in the sediment source area between 99 Ma and 72 Ma. Rapid cooling of the metamorphic source area at rates of 35 to over 100°C/m.y. between 84 and 63 Ma was required to supply these metamorphic zircon to the basin. The geological history of the sediment source region defined by the rim populations (age of metamorphism and exhumation rate) is inconsistent with previously proposed sediment source areas for the Nanaimo Group in southern (Mojave region) or northern Laurentia (Lehmi Subbasin). We hypothesize that the sediment source area was the adjacent Coast Mountains Batholith and a metasedimentary rock, similar to the Pelona‐Orocopia‐Rand‐type schists, that was exhumed during the Late Cretaceous.

Phylogenetic analysis of the distribution of deadly amatoxins among the little brown mushrooms of the genus Galerina.

Some but not all of the species of 'little brown mushrooms' in the genus Galerina contain deadly amatoxins at concentrations equaling those in the death cap, Amanita phalloides. However, Galerina's ~300 species are notoriously difficult to identify by morphology, and the identity of toxin-containing specimens has not been verified with DNA barcode sequencing. This left open the question of which Galerina species contain toxins and which do not. We selected specimens for toxin analysis using a preliminary phylogeny of the fungal DNA barcode region, the ribosomal internal transcribed spacer (ITS) region. Using liquid chromatography/mass spectrometry, we analyzed amatoxins from 70 samples of Galerina and close relatives, collected in western British Columbia, Canada. To put the presence of toxins into a phylogenetic context, we included the 70 samples in maximum likelihood analyses of 438 taxa, using ITS, RNA polymerase II second largest subunit gene (RPB2), and nuclear large subunit ribosomal RNA (LSU) gene sequences. We sequenced barcode DNA from types where possible to aid with applications of names. We detected amatoxins only in the 24 samples of the G. marginata s.l. complex in the Naucoriopsis clade. We delimited 56 putative Galerina species using Automatic Barcode Gap Detection software. Phylogenetic analysis showed moderate to strong support for Galerina infrageneric clades Naucoriopsis, Galerina, Tubariopsis, and Sideroides. Mycenopsis appeared paraphyletic and included Gymnopilus. Amatoxins were not detected in 46 samples from Galerina clades outside of Naucoriopsis or from outgroups. Our data show significant quantities of toxin in all mushrooms tested from the G. marginata s.l. complex. DNA barcoding revealed consistent accuracy in morphology-based identification of specimens to G. marginata s.l. complex. Prompt and careful morphological identification of ingested G. marginata s.l. has the potential to improve patient outcomes by leading to fast and appropriate treatment.

Postseismic Deformation due to the 2012 Mw 7.8 Haida Gwaii and 2013 Mw 7.5 Craig Earthquakes and its Implications for Regional Rheological Structure

AbstractObservations of ∼7 years of postseismic deformation following the 2012 M w 7.8 Haida Gwaii and 2013 M w 7.5 Craig earthquakes in western British Columbia and southeastern Alaska provides insight into the regional rheologic structure and seismological hazards. A stress‐driven afterslip‐only model cannot alone explain rates or spatial patterns of the far field and later stage postseismic deformation measured by Global Positioning System (GPS). We thus develop an integrated model that fits the observations by combining afterslip on the deeper extension of the faults and distributed viscous flow in the asthenosphere. The best‐fit integrated model has a 60‐km thick lithosphere overlying a Burgers body asthenosphere with a Maxwell viscosity of 2 × 1019 Pa s (0.8–3 × 1019 Pa s at 95% confidence), with a Kelvin viscosity assumed equal to 10% of that value. These values are in good agreement with rheological models derived from glacial isostatic adjustment data. The early, near‐field postseismic deformation from both events is dominated by their corresponding afterslip, however, throughout the Craig postseismic period, the dominant mechanism in the far field is viscoelastic relaxation. For the intermediate region between the two earthquakes, both events contribute to the observed postseismic displacements. Because there was no obvious afterslip following the Haida Gwaii event or known large historical earthquakes on the southernmost part of the QCF, this region continues to have great potential to suffer a large earthquake in the future.

Focused fluid flow and methane venting along the Queen Charlotte fault, offshore Alaska (USA) and British Columbia (Canada)

AbstractFluid seepage along obliquely deforming plate boundaries can be an important indicator of crustal permeability and influence on fault-zone mechanics and hydrocarbon migration. The ∼850-km-long Queen Charlotte fault (QCF) is the dominant structure along the right-lateral transform boundary that separates the Pacific and North American tectonic plates offshore southeastern Alaska (USA) and western British Columbia (Canada). Indications for fluid seepage along the QCF margin include gas bubbles originating from the seafloor and imaged in the water column, chemosynthetic communities, precipitates of authigenic carbonates, mud volcanoes, and changes in the acoustic character of seismic reflection data. Cold seeps sampled in this study preferentially occur along the crests of ridgelines associated with uplift and folding and between submarine canyons that incise the continental slope strata. With carbonate stable carbon isotope (δ13C) values ranging from −46‰ to −3‰, there is evidence of both microbial and thermal degradation of organic matter of continental-margin sediments along the QCF. Both active and dormant venting on ridge crests indicate that the development of anticlines is a key feature along the QCF that facilitates both trapping and focused fluid flow. Geochemical analyses of methane-derived authigenic carbonates are evidence of fluid seepage along the QCF since the Last Glacial Maximum. These cold seeps sustain vibrant chemosynthetic communities such as clams and bacterial mats, providing further evidence of venting of reduced chemical fluids such as methane and sulfide along the QCF.

Late Cretaceous to Paleocene Tectonometamorphic Evolution of the Blanchard River Assemblage, Southwest Yukon: New Insight into the Terminal Accretion of Insular Terranes in the Northern Cordillera

Abstract The Intermontane-Insular terrane boundary stretches over 2000 kilometers from British Columbia to Alaska in the western Cordillera. Juxtaposed between these terranes is a series of Jura-Cretaceous basinal and arc assemblages that record a complicated and contested tectonic evolution related to the Mesozoic-Paleocene accretionary history of northwestern North America. In southwest Yukon, west-verging thrust faults facilitated structural stacking of the Yukon-Tanana terrane over these basinal assemblages, including the Early Cretaceous Blanchard River assemblage. These previously undated compressional structures are thought to be related to the final collapse of the Jura-Cretaceous basins and the tectonic burial of the Blanchard River assemblage resulting in amphibolite facies metamorphism. New in situ U-Th-Pb monazite ages record at least three tectonic events: (1) the tectonic burial of the Blanchard River assemblage to amphibolite facies conditions between 83 and 76 Ma; (2) peak burial was followed by regional exhumation at ca. 70-68 Ma; and (3) intense heating and ca. 63-61 Ma low-pressure contact metamorphism attributed to the intrusion of the voluminous Ruby Range suite, which is part of the northern Coast Mountains batholith. The tectonometamorphic evolution recorded in the Blanchard River assemblage can be correlated to tectonism within southwest Yukon and along the length of the Insular-Intermontane boundary from western British Columbia through southwestern Yukon and Alaska. In southwest Yukon, these results suggest an asymmetric final collapse of Jura-Cretaceous basins during the Late Cretaceous, which relates to the terminal accretion of the Insular terranes as they moved northward.

Epiphyllous bryophytes in Arboretum Mlyňany (Slovakia)

Epiphyllous bryophytes in Arboretum Mlyňany (Slovakia)

Cryptic and extensive hybridization between ancient lineages of American crows.

Most species and therefore most hybrid zones have historically been defined using phenotypic characters. However, both speciation and hybridization can occur with negligible morphological differentiation. Recently developed genomic tools provide the means to better understand cryptic speciation and hybridization. The Northwestern Crow (Corvus caurinus) and American Crow (Corvus brachyrhynchos) are continuously distributed sister taxa that lack reliable traditional characters for identification. In this first population genomic study of Northwestern and American crows, we use genomic SNPs (nuDNA) and mtDNA to investigate the degree of genetic differentiation between these crows and the extent to which they may hybridize. Our results indicate that American and Northwestern crows have distinct evolutionary histories, supported by two nuDNA ancestry clusters and two 1.1%-divergent mtDNA clades dating to the late Pleistocene, when glacial advances may have isolated crow populations in separate refugia. We document extensive hybridization, with geographic overlap of mtDNA clades and admixture of nuDNA across >900km of western Washington and western British Columbia. This broad hybrid zone consists of late-generation hybrids and backcrosses, but not recent (e.g., F1) hybrids. Nuclear DNA and mtDNA clines had concordant widths and were both centred in southwestern British Columbia, farther north than previously postulated. Overall, our results suggest a history of reticulate evolution in American and Northwestern crows, perhaps due to recurring neutral expansion(s) from Pleistocene glacial refugia followed by lineage fusion(s). However, we do not rule out a contributing role for more recent potential drivers of hybridization, such as expansion into human-modified habitats.

Climate indices to characterize climatic changes across southern Canada

AbstractThe present study analyses the impacts of past and future climate change on extreme weather events for southern parts of Canada from 1981 to 2100. A set of precipitation and temperature‐based indices were computed using the downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) multi‐model ensemble projections at 8 km resolution over the 21st Century for two representative concentration pathway (RCP) scenarios: RCP4.5 and RCP8.5. The results show that this region is expected to experience stronger warming and a higher increase in precipitation extremes in future. Generally, projected changes in minimum temperature will be greater than changes in maximum temperature, as shown by respective indices. A decrease in frost days and an increase in warm nights will be expected. By 2100 there will be no cool nights and cool days. Daily minimum and maximum temperatures will increase by 12 and 7°C, respectively, under the RCP8.5 scenario, when compared with the reference period 1981–2000. The highest warming in minimum temperature and decrease in cool nights and days will occur in Ontario and Quebec provinces close to the Great Lakes and Hudson Bay. The highest warming in maximum temperature will occur in the southern parts of Alberta and Saskatchewan. Annual total precipitation is expected to increase by about 16% and the occurrence of heavy precipitation events by five days. The highest increase in annual total precipitation will occur in the northern parts of Ontario and Quebec and in western British Columbia.

Plate boundary localization, slip-rates and rupture segmentation of the Queen Charlotte Fault based on submarine tectonic geomorphology

Linking fault behavior over many earthquake cycles to individual earthquake behavior is a primary goal in tectonic geomorphology, particularly across an entire plate boundary. Here, we examine the 1150-km-long, right-lateral Queen Charlotte-Fairweather fault system using comprehensive multibeam bathymetry data acquired along the Queen Charlotte Fault (QCF) offshore southeastern Alaska and western British Columbia. Fine-scale analysis of tectonic geomorphology allowed us to identify and reconstruct 184 strike-slip piercing points over a 630 km stretch of the QCF. Age constraints from glacial recession and offshore sedimentation patterns yield a consistent slip-rate of ∼50–57 mm/yr since ∼17–12 ka, the fastest rate for a continent-ocean strike-slip fault on Earth. These slip-rates equal or exceed estimates of Pacific-North America (PA-NA) relative motion from global plate reconstructions, indicating that PA-NA motion is highly localized. The QCF cuts the seafloor along a narrow and unusually straight trace for its entire length and multiple fault traces are observed only at local step-overs. The geometry and behavior of the QCF over many earthquake cycles is simple and typical of mature faults with relatively homogeneous stress fields. Since the QCF is the primary PA-NA plate boundary, we used the trace of the QCF to define the small circle path for relative plate motion and computed the associated Euler pole. Predicted along-strike obliquity variations based on the new pole agree with observed tectonic geomorphology and suggest that previous global plate reconstructions overestimated the degree of oblique convergence along the QCF. We also find that subtle, long-wavelength (75–150 km) bends and discrete step-overs appear to define the endpoints of M>7 earthquakes, suggesting that obliquity and resultant fault geometry may control rupture segmentation and asperity development. Lastly, the agreement between predicted obliquity and tectonic geomorphology along the entire length of QCF compelled a reevaluation of regional tectonic models. In the north, the eastern Yakatat Terrane appears to be translating northwest with the Pacific plate, and slip transferred from the QCF to the Fairweather Fault results in ∼20 mm/yr of convergence along the southern St. Elias mountains. In the south, we predict a reduced rate of convergence along the QCF west of Haida Gwaii (∼5–6 mm/yr of shortening, on average) relative to previous studies. Our results support a model for transpression and strike-slip partitioning along the edge of a hot and weak Pacific Plate, leading to crustal thickening and growth of the Queen Charlotte Terrace to the west of Haida Gwaii.

Detection of ‘Candidatus Ehrlichia khabarensis’ in rodents and ticks removed from rodents in British Columbia, Canada

‘Candidatus Ehrlichia khabarensis’ was first described from rodents and insectivores in the Far East territory of Khabarovsk on the Russian Pacific Coast. Here we report the detection of DNA from this microorganism in rodents and fed ticks collected from rodents in British Columbia, Canada in 2013–2014. ‘Candidatus Ehrlichia khabarensis’ was detected in (i) a female Ixodes angustus tick collected from a Peromyscus maniculatus; (ii) a female Dermacentor andersoni tick collected from a Perognathus parvus; (iii) a pool of 2 larval Ixodes pacificus ticks collected from a single P. maniculatus; and (iv) a pool of 3 nymphal I. pacificus ticks collected from a single P. maniculatus. Three of these four rodents (2 P. maniculatus and 1 P. parvus) with infected ticks also had evidence of ‘Candidatus Ehrlichia khabarensis’ in at least one tissue type. The infected P. maniculatus and Ixodes ticks came from the Vancouver area in western British Columbia and the P. parvus and Dermacentor tick from an inland site in central British Columbia. Although it remains to be determined whether ‘Candidatus Ehrlichia khabarensis’ has any negative impacts on wildlife, domestic animals or humans, we note that all three tick species found to contain the DNA of this microorganism are known to bite humans. Future detection of this microorganism either in ticks collected from rodents and allowed to molt to the next life stage prior to being tested, or from host-seeking ticks, is required to determine if it can survive the tick’s molt after being ingested via an infectious blood meal.

Grylloblattodea of Canada.

The enigmatic insect order Grylloblattodea comprises two described species in Canada, which are limited to the Montane Cordillera and Pacific Maritime ecozones. One of the described species has three Canadian subspecies of uncertain taxonomic ranking, and there are two additional undescribed or unreported species known in close proximity to the Canadian border in western Alberta and British Columbia that likely also occur in Canada. Thus, as much as 50% of the total taxonomic diversity of Grylloblattodea in Canada is still undocumented. Targeted surveys and taxonomic work, as well as studies that describe the ecology and conservation status of Grylloblattodea are important goals for future research.

Comparison of chemotherapy use, cost, and survival in patients with metastatic colorectal cancer in Western Washington and British Columbia.

LBA3579 Background: Few studies have directly compared health care utilization, costs, and outcomes between geographically similar patients (pts) treated in the U.S.’ multi-payer health system versus Canada’s single-payer system. Using cancer registry and claims data, we assessed systemic therapy (ST) use, cost, and survival for metastatic colorectal cancer (mCRC) pts in Western Washington (WW) and British Columbia (BC). Methods: Pts age ≥ 18 diagnosed with mCRC in 2010 and later were identified from 1) the BC Cancer Agency database and 2) a regional database linking WW SEER to claims from two large commercial insurers. Demographic and treatment characteristics for the two populations were compared using two-sample T tests. ST costs (first-line and lifetime) were expressed as mean per patient per month costs; Canadian costs were expressed in US dollars using the Purchasing Power Parity for Health in 2009. Median survival was reported for both populations. Results: 1622 BC pts and 575 WW pts were included in the analysis. BC pts were more likely to be older (median age 60 vs 66) and male (57% vs 48%, p = < 0.01). A greater proportion of WW versus BC pts received ST (79% vs. 68%, p < 0.01). FOLFIRI plus bevacizumab was the most common first-line regimen in BC (32%) while FOLFOX was the most common first-line regimen in WW (39%). The mean monthly cost of first-line therapy per patient was significantly higher in WW than BC ($12,345 vs $6,195, p = < 0.01), and this was true for all regimens assessed. Mean lifetime monthly ST costs were significantly higher in WW ($7,883 vs $4,830, p = < 0.01). There was no difference in median overall survival between populations among those receiving ST (21.4 months (95% CI 18.0-26.2) in WW and 22.1 months (20.5-23.7) in BC) or among those not receiving ST (5.4 months (2.4-7.7) WW versus 6.3 months (5.2-7.3) BC). Conclusions: Utilization and cost of ST for mCRC was significantly higher for patients in WW compared to BC without differences in overall survival in treated and untreated patients.

Slope failure and mass transport processes along the Queen Charlotte Fault Zone, western British Columbia

Abstract Multibeam echosounder (MBES) images, 3.5 kHz seismic-reflection profiles and piston cores obtained along the southern Queen Charlotte Fault Zone are used to map and date mass-wasting events at this transform margin – a seismically active boundary that separates the Pacific Plate from the North American Plate. Whereas the upper continental slope adjacent to and east (upslope) of the fault zone offshore of the Haida Gwaii is heavily gullied, few large-sized submarine landslides in this area are observed in the MBES images. However, smaller submarine seafloor slides exist locally in areas where fluid flow appears to be occurring and large seafloor slides have recently been detected at the base of the steep continental slope just above its contact with the abyssal plain on the Queen Charlotte Terrace. In addition, along the subtle slope re-entrant area offshore of the Dixon Entrance shelf bathymetric data suggest that extensive mass wasting has occurred in the vicinity of an active mud volcano venting gas. We surmise that the relative lack of submarine slides along the upper slope in close proximity to the Queen Charlotte Fault Zone may be the result of seismic strengthening (compaction and cohesion) of a sediment-starved shelf and slope through multiple seismic events.

Tectonically controlled initiation of contemporaneous deep‐water channel systems along a Late Cretaceous continental margin, western British Columbia, Canada

AbstractSubmarine channel‐systems are globally prevalent on continental margins and their deposits record the transfer of significant volumes of sediment from continental catchments to deep‐water environments. These deposits contain signals of past events that can provide critical insight into the geological history of an area, including the long‐term (>1 Ma) controls on sedimentation. Well‐exposed outcrops of the Late Cretaceous Nanaimo Group, British Columbia, Canada, provide an opportunity to investigate long‐term sediment‐routing in a tectonically active setting. This study combines detrital zircon geochronology with stratigraphic analysis to establish a robust, basin‐wide palaeogeographic framework that constrains the timing and distribution of coarse‐grained sediment transport and deposition in the Nanaimo forearc basin. Three south‐west trending submarine conduits are documented along a 135 km long strike‐oriented transect, parallel to the north‐west/south‐east trending basin. Composite conduit deposits are 350 to 700 m thick, 4 to 16 km wide, and record substantial delivery of coarse‐grained detritus (up to boulder‐sized clasts) within submarine channel‐levée systems. Maximum depositional ages derived from detrital zircon datasets constrain contemporaneous sediment transfer and deposition at each conduit location, which spanned between 73·5 ± 1·3 Ma to 69·1 ± 1·1 Ma around the Campanian–Maastrichtian boundary. Submarine conduits are spaced at 40 km and 70 km, and were likely connected to fluvial drainage systems sourced in uplifted catchments. Widespread, coarse‐grained deposits suggest that surface uplift associated with concurrent regional events (such as deformation and/or magma emplacement) along the North American margin may have promoted sediment delivery to the deep‐water basin. Comparisons to modern and ancient analogues support palaeogeographic interpretations, as well as the interpretation that pervasive coarse‐grained deep‐water sediment delivery was linked to tectonic activity. The integrated stratigraphic–geochronological approach used provides unique insight into the influence of regional tectonics on continental margin physiography and the nature of deep‐water sediment dispersal.

Sediment underthrusting within a continental magmatic arc: Coast Mountains batholith, British Columbia

AbstractThough continental magmatic arcs are factories for new continental crust, a significant proportion of continental arc magmas are recycled from supracrustal material. To evaluate the relative contributions of retroarc underthrusting and trench side partial sediment subduction for introducing supracrustal rocks to the middle and lower crust of continental magmatic arcs, we present results from the deeply exposed country rocks of the Coast Mountains batholith of western British Columbia. Prior work demonstrates that these rocks underwent widespread partial melting that contributed to the Coast Mountains batholith. We utilize U‐Pb zircon geochronology, Sm‐Nd thermochronology, and field‐based studies to document the protoliths and early burial history of amphibolite and granulite‐facies metasedimentary rocks in the Central Gneiss Complex. U‐Pb detrital zircon data from the structurally highest sample localities yielded ~190 Ma unimodal age peaks and suggest that retroarc rocks of the Stikine terrane constitute a substantial portion of the Central Gneiss Complex. These supracrustal rocks underwent thrust‐related burial and metamorphism at >25 km depths prior to ~80 Ma. These rocks may also be underlain at the deepest exposed structural levels by Upper Cretaceous metasedimentary rocks, which may have been emplaced as a result of trench side underplating or intraarc burial. These results further our understanding of the mechanisms of material transport within the continental lithosphere along Cordilleran subduction margins.

An alternative approach to site factors for NBCC 2015

The site amplification factors in the 2015 edition of the National Building Code of Canada (NBCC 2015) for South Western British Columbia (SWBC) were developed using only the single site term associated with the ground motion prediction equation (GMPE) for crustal sources. The seismic hazard in SWBC is derived from three source types; crustal, subduction intraplate, and subduction interface sources. Therefore site factors based only on a crustal site term are approximate. This study was conducted to assess the degree of approximation. Alternative site amplification factors for Vancouver and Victoria, British Columbia were calculated using site specific look-up tables incorporating all the GMPEs associated with each seismic source type and their associated site terms. The alternative site factors are significantly greater than those given in NBCC 2015 for periods 0.3 s, 0.5 s, and 1.0 s. These results suggest that the process for calculating site amplification factors should be reassessed by the committee currently reviewing seismic hazard for NBCC 2020.

Sturgeon Bank, Fraser River Delta, BC, Canada: 150 Years of Human Influences on Salt Marsh Sedimentation

Atkins, R.J.; Tidd, M., and Ruffo, G., 2016. Sturgeon Bank, Fraser River Delta, BC, Canada: 150 Years of Human Influence on Salt Marsh Sedimentation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 790–794. Coconut Creek (Florida), ISSN 0749-0208.The Fraser River Delta in south western British Columbia, Canada, is a relatively recent geologic feature being only approximately 10,000 years old. The delta environment, and the intertidal banks, are the cumulative effect of flood and sediment discharges over the post-glacial interval. The salt marsh of Sturgeon Bank, on the northwest side of the delta, has been identified as under threat from erosion. The occurrence, cause and extent of erosion have been a subject of speculation, investigation and conclusion for several decades; however, dissenting opinions on the persistence of erosion over the last fifty years are numerous. To explore potential causes of the erosion further, publically available historical datasets of natural phenomena were re-examined relative to records of human activities to enable development of a conceptual model. Historical datasets of natural phenomena included sedimentary geology, post-glacial history, bathymetry, flood discharge records, sediment discharge/basin sediment yield, sediment grain size data, wind-waves, and tides. Human activity, stretching back to the late 1800's, included navigation dredging, aggregate resource dredging, river training, river diversion, flood protection dyking, land-use changes, and ongoing habitat management activities. From this review, a conceptual model of physical constraints on deltaic environments was developed. The various phenomena are discussed, the integration of those phenomena as processes affecting deltaic habitat explored, and potential management strategies identified to address the sedimentary consequences of the last 150 years of human influence on the salt marshes of Sturgeon Bank.

Early Albian (Early Cretaceous) douvilleiceratid ammonites from Haida Gwaii, British Columbia, Canada

AbstractThe early Albian to mid-Albian cosmopolitan genusDouvilleicerasis represented in the Haida Gwaii archipelago of western British Columbia by five species,D.mammillatum(Schlotheim),D.offarcinatum(White),D.scabrosumCasey,D.spiniferum(Whiteaves), andD. aff.spiniferum(Whiteaves). Specimens of one of these taxa,D.spiniferum, are particularly abundant on Haida Gwaii and the species is discussed with respect to its morphological variability and ontogenetic development. The important morphological features for taxonomic criteria of the genusDouvilleicerasare the mode of tuberculation, the pattern of ribbing, and the proportions of the shell in the middle growth stage.