Long Period Long Duration (LPLD) signals are unusual seismic events that can be observed during hydraulic fracturing. These events are very similar in appearance to tectonic tremors sequences, which were first observed in subduction zones. Their nature is not well known. LPLD might be related to the productivity of the reservoir. Different methods of the LPLD events’ detection recorded during hydraulic fracturing are presented. The author applied two methods for LPLD detection–Butterworth filtering and Continuous Wavelet Transform (CWT). Additionally, a new approach to LPLD events detection–instantaneous seismic attributes–was used, common in a classical seismic interpretation but not in microseismic monitoring. 相似文献
There are over 500 species of arthropods recorded from Svalbard. These animals overwinter either within the soil or on the ground surface, and have to tolerate an environment where the ground is frozen for over 9 months each year. Three cold-tolerance strategies have been described from Svalbard invertebrates: freeze avoidance, freeze tolerance and desiccation. Once in a cold-tolerant state the animals can be extremely cold tolerant in terms of both minimum exposure temperature and period of exposure. How the overwintering capabilities of these animals will be affected by climate changes during the next 100 years, as predicted by climate models, is not yet known. Four principle factors with an impact on overwintering of the terrestrial arthropod fauna are outlined here: (1) warmer winter temperatures, with an increased frequency of extreme events such as freeze–thaw cycles and surface icing; (2) changes in snow fall and snow lie; (3) pollutant load; and (4) dispersal of invertebrates to Svalbard. Finally, areas where further research is required are highlighted: including the development of controlled multi-season field experiments; effect of freeze–thaw cycles; changes in thickness and distribution of snow lie, with the subsequent effects on duration of the summer period; chill susceptibility of soil arthropods; assessing potential colonizing species and the likelihood of these species becoming established; assessing the effect of gene flow from surrounding populations; interactions between pollution and cold tolerance; anoxia stress; and the genetics of cold tolerance. 相似文献
Using the characteristic earthquake model, we calculate the probability of occurrence of earthquakes Mw > 5.5 for individual fault sources in the Central Apennines for the 30-year period (2007–2037). We show the effect of time-dependent
and time-independent occurrence (Brownian passage time (BPT) and Poisson) models together with uncertain slip rates and uncertain
maximum magnitudes and, hence, uncertain recurrence times. In order to reduce the large prior geological slip rate uncertainty
distribution for most faults, we obtain a posterior slip rate uncertainty distribution using a likelihood function obtained
from regional historical seismicity. We assess the uncertainty of maximum magnitude by assuming that the uncertainty in fault
width and length are described by a normal distribution with standard deviation equal to ±20% of the mean values. We then
estimate the uncertainties of the 30-year probability of occurrence of a characteristic event using a Monte Carlo procedure.
Uncertainty on each parameter is represented by the 16th and the 84th percentiles of simulated values. These percentiles bound
the range that has a 68% probability of including the real value of the parameter. We do these both for the Poisson case and
for the BPT case by varying the aperiodicity parameter (α value) using the values 0.3, 0.5, and 0.7. The Bayesian posterior slip rate uncertainties typically differ by a factor of
about 2 from the 16th to the 84th percentile. Occurrence probabilities for the next 30 years at the 84th percentile typically
range from 1% to 2% for faults where the Poisson model dominates and from 2% to 21% where one of the BPT models dominates.
The uncertainty in occurrence probability under the time-dependent hypothesis is very large, when measured by the ratio of
the 84th to the 16th percentile, frequently being as much as two orders of magnitude. On the other hand, when measured by
standard deviation, these standard deviations range from 2% to 6% for those faults whose elapsed time since previous event
is large, but always 2% or less for faults with relatively recent previous occurrence, because the probability of occurrence
is always small. 相似文献
For more than four decades, the reporting of 14C dates on marine molluscs from Arctic Canada has been notable for the lack of consistently applied marine reservoir corrections. We propose that the common approach of reporting Canadian Arctic marine 14C dates using presumed time-invariant reservoir corrections be abandoned in favour of calibration of 14C dates, using the current standard protocol. This approach best facilitates inter- and intra-regional correlation, and correlation with other geochronometers. In order to enable the consistent calibration of marine 14C dates from Arctic Canada, we analysed a 14C database of 108 marine mollusc samples collected live between 1894 and 1956, and determined regional reservoir offset values (ΔR) for eight oceanographically distinct regions. The following new ΔR values should be used for 14C calibration: NW Canadian Arctic Archipelago, 335 ± 85 yrs; Foxe Basin, 310 ± 90 yrs; NE Baffin Island, 220 ± 20 yrs; SE Baffin Island, 150 ± 60 yrs; Hudson Strait, 65 ± 60 yrs; Ungava Bay, 145 ± 95 yrs; Hudson Bay, 110 ± 65 yrs; and James Bay, 365 ± 115 yrs. 相似文献
Complex links between the top-down and bottom-up forces that structure communities can be disrupted by anthropogenic alterations
of natural habitats. We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass
(Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility.
At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment
increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers
did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic
seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were
more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food
web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure
in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in
this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships,
and, ultimately, the productivity values of the ecosystem. 相似文献
The opportunity and the advantages of applying base isolation technologies developed for civil structures to small objects are investigated and some considerations related to the scale effects are discussed. A series of experimental tests carried out at SRMD facility in San Diego are presented with the aim to investigate the dynamic response of a system designed to simulate a sculpture isolated by means of Double Concave Curved Surface Sliders. Such devices are specifically re-designed to fit the peculiar situation of light weight objects. In particular the samples used in the experimentation are designed with geometric and inertia characteristics fit for representing the Michelangelo’s sculptures exposed at the “Galleria dell’Accademia” in Florence, Italy. Finally, the main aspects concerning the numerical simulation of the seismic response of the proposed isolated system are discussed, also to investigate the efficiency of the existing numerical models, which are developed for traditional devices, when they are applied on such small and particular objects. The results of the experimental/numerical campaign show a general efficiency of the isolation system in terms of limiting the transferred action. Further study is needed to understand more clearly some local unexpected phenomena emerged from the experimental tests. 相似文献
First-arrival traveltime tomography was applied to high-resolution seismic data acquired over a known quick-clay landslide scar near the Göta River in southwest Sweden in order to reveal the geometry and physical properties of clay-related normally consolidated sediments. Investigated area proved to be a challenging environment for tomographic imaging because of large P-wave velocity variations, ranging from 500 to 6000 m/s, and relatively steeply-dipping bedrock. Despite these challenges, P-wave velocity models were obtained down to ca. 150 m for two key 2D seismic profiles (each about 500-m long) intersecting over the landslide scar. The models portrait the sandwich-like structure of marine clays and coarse-grained consolidated sediments, but the estimated resolution (20 m) is too small to distinguish thin layers within this structure. Modelled velocity structures match well the results of reflection seismic processing and resistivity tomography available along the same profiles. 相似文献
ABSTRACTThe relative location of commercial properties as the distance to the metro station as well as its absolute location as the address in the Central Business District (CBD) is expected to influence its valuation. We apply the advanced spatial econometric methodology, based on micro geo-located data, to the office rental transaction data from London in 2015. We use different spatial information on the local and global neighbourhood in order to estimate the spatial hedonic valuation model and test the strength of spatial spillovers and location effects on office fees. For offices in London in 2015, geographical factors may raise the price by 50%, as every next 100 m to the metro cost an additional 0.7 ? per ft2 per year and the CBD location raises the cost for ca. 20 ? per ft2 per year. 相似文献
We study the spatio-temporal variability of Atmospheric Rivers (ARs) and associated integrated water vapor and atmospheric parameters over the Euro-Atlantic region using long-term reanalysis datasets. Winds, temperature, and specific humidity at different pressure levels during 1979–2018 are used to study the water vapor transport integrated between 1000 and 300 hPa (IVT300) in mapping ARs. The intensity of ARs in the North Atlantic has been increasing in recent times (2009–2018) with large decadal variability and poleward shift (~ 5° towards the North) in landfall during 1999–2018. Though different reanalysis datasets show similar spatial patterns of IVT300 in mapping ARs, bias in specific humidity and wind components led to IVT300 mean bias of 50 kg m−1 s−1 in different reanalysis products compared to ERA5. The magnitude of winds and specific humidity in the lower atmosphere (below 750 hPa) dominates the total column water vapor and intensity of ARs in the North Atlantic. Reanalysis datasets in the central North Atlantic show an IVT300 standard deviation of 200 kg m−1 s−1 which is around 33% of the ARs climatology (~ 600 kg m−1 s−1). Though ARs have a higher frequency of landfalling over Western Europe in winter half-year, the intensity of IVT300 in winter ARs is 3% lower than the annual mean. The lower frequency of ARs in the summer half-year shows 3% higher IVT300 than the annual mean. While ARs in the North Atlantic show a strong decadal change in frequency and path, the impact of the North Atlantic Oscillation (NAO) and Scandinavian blocking on the location of landfall of ARs are significant. Furthermore, there is a strong latitudinal dependence of the source of moisture flux in the open ocean, contributing to the formation and strengthening ARs.