ALBERT

Beschreibung: On 28 October 2012, an M w  7.8 earthquake occurred off the west coast of Haida Gwaii, British Columbia. Although past large events at this margin reflect strike-slip motion between the Pacific and North American plates (e.g., 1949 M s  8.1), this earthquake involved low-angle thrust faulting with a slip direction almost perpendicular to the margin, a consequence of slip partitioning at this obliquely convergent margin. To refine regional source models, we investigated the coseismic and postseismic displacements using a network of Global Positioning System (GPS) sites. Coseismic movement at the campaign site closest to the coast and about 30 km from the epicenter is 115 cm to the south-southwest, with 30 cm of subsidence. The only continuously recording GPS station on Haida Gwaii at the time of the earthquake, about 80 km from the epicenter, provides a robust coseismic displacement estimate of 22 cm to the south-southwest. The coseismic results are consistent with a shallow-dipping thrust rupture underlying the Queen Charlotte terrace, immediately seaward of the Queen Charlotte fault. These results allowed us to update rupture models that were originally derived from seismic waveforms and tsunami data. Estimates of cumulative postseismic horizontal displacements over about one year from seven sites are up to 6 cm, with a systematic along-strike variation in azimuth from south-southwest to southeast from north to south in the study area. Besides viscoelastic stress relaxation, these postseismic trends may indicate afterslip on the deeper plate interface beneath northern Moresby Island and possibly aseismic slip along the Queen Charlotte or subparallel faults offshore of southern Moresby Island. Online Material: Figures of three-component daily position estimates from Bernese analysis at Global Positioning System tracking stations on Haida Gwaii and the adjacent mainland.

Beschreibung: The thickness and equivalent global sea level contribution of an improved model of the central and northern Laurentide Ice Sheet is constrained by 24 relative sea level histories and 18 present-day GPS-measured vertical land motion rates. The final model, termed Laur16, is derived from the ICE-5G model by holding the timing history constant and iteratively adjusting the thickness history, in four regions of northern Canada. In the final model, the last glacial maximum (LGM) thickness of the Laurentide Ice Sheet west of Hudson Bay was ~3.4–3.6 km. Conversely, east of Hudson Bay, peak ice thicknesses reached ~4 km. The ice model thicknesses inferred for these two regions represent, respectively, a ~30 per cent decrease and an average ~20–25 per cent increase to the load thickness relative to the ICE-5G reconstruction, which is generally consistent with other recent studies that have focussed on Laurentide Ice Sheet history. The final model also features peak ice thicknesses of 1.2–1.3 km in the Baffin Island region, a modest reduction relative to ICE-5G and unchanged thicknesses for a region in the central Canadian Arctic Archipelago west of Baffin Island. Vertical land motion predictions of the final model fit observed crustal uplift rates well, after an adjustment is made for the elastic crustal response to present-day ice mass changes of regional ice cover. The new Laur16 model provides more than a factor of two improvement of the fit to the RSL data ( 2 measure of misfit) and a factor of nine improvement to the fit of the GPS data (mean squared error measure of fit), compared to the ICE-5G starting model. Laur16 also fits the regional RSL data better by a factor of two and gives a slightly better fit to GPS uplift rates than the recent ICE-6G model. The volume history of the Laur16 reconstruction corresponds to an up to 8 m reduction in global sea level equivalent compared to ICE-5G at LGM.

Beschreibung: New, more socially-acceptable technologies are being developed to suppress horticultural pests, because suppression is technically difficult with current technologies, especially in urban areas. One technique involves the release of sterile insects to prevent offspring in the next generation. This technology involves aerial or ground release systems, but this could also create issues for the public. This study investigated community perceptions of a recently-introduced response to codling moth control in New Zealand—Sterile Insect Technique (SIT). Community attitudes to SIT were examined in Hastings, New Zealand, in April, 2018. Eighty-six detailed interviews were undertaken with a random sample of households. This community was very willing (98% agreement) to host a sex pheromone trap in their gardens, and condoned regular visits to monitor traps. Attitudes to SIT were very positive (98% in favor). Once explained, the concept of using unmanned aerial vehicles to deliver sterile insects was also acceptable (98%) to the community. Use of unmanned aerial vehicles to release sterile insects during a hypothetical incursion response of an exotic fruit fly was also supported at 98% by respondent householders. Investigation of community attitudes can be valuable to guide practitioners in determining suitable technologies before an area-wide programme is launched.

Beschreibung: This paper documents the methodology of computing sea-level rise allowances for Atlantic Canada in the 21st century under conditions of uncertain sea-level rise. The sea-level rise allowances are defined as the amount by which an asset needs to be raised in order to maintain the same likelihood of future flooding events as that site has experienced in the recent past. The allowances are determined by combination of the statistics of present tides and storm surges (storm tides) and the regional projections of sea-level rise and associated uncertainty. Tide-gauge data for nine sites from the Canadian Atlantic coast are used to derive the scale parameters of present sea-level extremes using the Gumbel distribution function. The allowances in the 21st century, with respect to the year 1990, were computed for the Intergovernmental Panel on Climate Change (IPCC) A1FI emission scenario. For Atlantic Canada, the allowances are regionally variable and, for the period 1990–2050, range between –13 and 38 cm while, for the period 1990–2100, they range between 7 and 108 cm. The negative allowances in the northern Gulf of St. Lawrence region are caused by land uplift due to glacial isostatic adjustment (GIA).

Beschreibung: On 28 October 2012, an Mw 7.8 earthquake occurred off the west coast of Haida Gwaii, British Columbia. Although past large events at this margin reflect strike‐slip motion between the Pacific and North American plates (e.g., 1949 Ms 8.1), this earthquake involved low‐angle thrust faulting with a slip direction almost perpendicular to the margin, a consequence of slip partitioning at this obliquely convergent margin. To refine regional source models, we investigated the coseismic and postseismic displacements using a network of Global Positioning System (GPS) sites. Coseismic movement at the campaign site closest to the coast and about 30 km from the epicenter is 115 cm to the south‐southwest, with 30 cm of subsidence. The only continuously recording GPS station on Haida Gwaii at the time of the earthquake, about 80 km from the epicenter, provides a robust coseismic displacement estimate of 22 cm to the south‐southwest. The coseismic results are consistent with a shallow‐dipping thrust rupture underlying the Queen Charlotte terrace, immediately seaward of the Queen Charlotte fault. These results allowed us to update rupture models that were originally derived from seismic waveforms and tsunami data. Estimates of cumulative postseismic horizontal displacements over about one year from seven sites are up to 6 cm, with a systematic along‐strike variation in azimuth from south‐southwest to southeast from north to south in the study area. Besides viscoelastic stress relaxation, these postseismic trends may indicate afterslip on the deeper plate interface beneath northern Moresby Island and possibly aseismic slip along the Queen Charlotte or subparallel faults offshore of southern Moresby Island.Online Material: Figures of three‐component daily position estimates from Bernese analysis at Global Positioning System tracking stations on Haida Gwaii and the adjacent mainland.

Beschreibung: Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

Beschreibung: The ocean load in glacial isostatic adjustment (GIA) modelling is represented by the so-called sea level equation (SLE). The SLE describes the mass redistribution of water between ice sheets and oceans on a deforming Earth. Despite various teams independently investigating GIA, there has been no systematic intercomparison among the numerical solvers of the SLE through which the methods may be validated. The goal of this paper is to present a series of synthetic examples designed for testing and comparing the numerical implementations of the SLE in GIA modelling. The 10 numerical codes tested combine various temporal and spatial parametrizations. The time-domain or Laplace-domain discretizations are used to solve the SLE through time, while spherical harmonics, finite differences or finite elements parametrize the GIA-related field variables spatially. The surface ice-water load and solid Earth’s topography are represented spatially either on an equiangular grid, a Gauss–Legendre or an equiarea grid with icosahedron-shaped spherical pixels. Comparisons are made in a series of five benchmark examples with an increasing degree of complexity. Due to the complexity of the SLE, there is no analytical solution to it. The accuracy of the numerical implementations is therefore assessed by the differences of the individual solutions with respect to a reference solution. While the benchmark study does not result in GIA predictions for a realistic loading scenario, we establish a set of agreed-upon results that can be extended in the future by including more complex case studies, such as solutions with realistic loading scenarios, the rotational feedback in the linear-momentum equation, and by considering a 3-D viscosity structure of the Earth’s mantle. The test computations performed so far show very good agreement between the individual results and their ability to capture the main features of sea-surface variation and the surface vertical displacement. The differences found can often be attributed to the different approximations inherent in the various algorithms. This shows the accuracy that can be expected from different implementations of the SLE, which helps to assess differences noted in the literature between predictions for realistic loading cases.