RESUMEN
Coastal deposits at Tofino, Ucluelet, and Port Alberni in Vancouver Island along the Cascadia subduction zone were re-examined to improve the earthquake history of the southwest coast of Canada. We found sand sheets interbedded within peat and mud, suggesting deposition by strong flows in a low-energy environment. Based on limiting maximum and minimum ages derived from plant macrofossils, the age of one of the sand sheets below the tsunami deposits of the great Cascadia earthquake in 1700 CE was estimated to be 1330-1430 CE. Onshore paleoseismic evidence has been documented in Vancouver Island, northern Washington, and northern Oregon during this period. However, the newly constrained age is between those of coseismic subsidence Y and W events in southern Washington, which have been recognized as the 1700 CE and the penultimate Cascadia earthquakes, respectively. Moreover, the new age partly overlaps with the age of offshore paleoseismic evidence for T2, interpreted to have originated from the penultimate Cascadia earthquake, based on offshore turbidite records. The new chronology prior to the 1700 CE Cascadia tsunami deposit from Vancouver Island contributes to a better understand of the timing of the penultimate Cascadia earthquake.
RESUMEN
This paper presents a novel approach to continuously monitor very slow-moving translational landslides in mountainous terrain using conventional and experimental differential global navigation satellite system (d-GNSS) technologies. A key research question addressed is whether displacement trends captured by a radio-frequency "mobile" d-GNSS network compare with the spatial and temporal patterns in activity indicated by satellite interferometric synthetic aperture radar (InSAR) and unmanned aerial vehicle (UAV) photogrammetry. Field testing undertaken at Ripley Landslide, near Ashcroft in south-central British Columbia, Canada, demonstrates the applicability of new geospatial technologies to monitoring ground control points (GCPs) and railway infrastructure on a landslide with small and slow annual displacements (<10 cm/yr). Each technique records increased landslide activity and ground displacement in late winter and early spring. During this interval, river and groundwater levels are at their lowest levels, while ground saturation rapidly increases in response to the thawing of surficial earth materials, and the infiltration of snowmelt and runoff occurs by way of deep-penetrating tension cracks at the head scarp and across the main slide body. Research over the last decade provides vital information for government agencies, national railway companies, and other stakeholders to understand geohazard risk, predict landslide movement, improve the safety, security, and resilience of Canada's transportation infrastructure; and reduce risks to the economy, environment, natural resources, and public safety.
RESUMEN
Light nonaqueous phase liquids (LNAPLs), such as fuels, are the source of much soil and groundwater contamination. Though the mobility of LNAPLs is limited in many environments, dissolved-phase components, such as benzene, can produce groundwater plumes that are more mobile than the LNAPL source. In such a setting, it is commonly assumed that recovery of the LNAPL will result in a reduction in risk associated with the dissolved phase. This paper synthesizes several existing multiphase and chemical transport solutions into a single linked methodology that predicts concentrations of soluble constituents within and downgradient of LNAPL source zones from dissolution of those constituents into groundwater flowing through and below LNAPL sources. This approach has been applied to a variety of LNAPL spill conditions. For biodegradable compounds, these analyses show that the period of time where the dissolved-phase plume is expanding is very small compared to the duration of most LNAPL sources, and that the downgradient extent is generally less than about 100 m for BTEX compounds. Therefore, the risk to receptors, as measured by the maximum downgradient extent of dissolved-phase plume or the maximum concentration of these compounds at a downgradient receptor, is generally unrelated to the longevity of the LNAPL sources. The maximum downgradient extent of the dissolved-phase plume is determined almost entirely by the groundwater velocity and the biodegradation rate. These analyses further demonstrate that recovery of LNAPL by hydraulic methods is often ineffective at reducing risk. Except in coarse-grained soils or intermediate soils with significant LNAPL saturations, free-product recovery approaches do not result in significant reductions in the longevity of downgradient dissolved-phase contamination. Further, for biodegradable constituents, remediation does not result in a near-term decrease in the downgradient extent of contamination. Cleanup methods that act to change the composition of the LNAPL source are more effective at reducing the downgradient concentrations, particularly for fine-grained soils or when LNAPL saturations are low.