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1.
The lack of earthquake-induced liquefaction features in Late Wisconsin and Holocene sediments in Genesee, Wyoming, and Allegany Counties suggests that the Clarendon–Linden fault system (CLF) did not generate large, moment magnitude, M≥6 earthquakes during the past 12,000 years. Given that it was the likely source of the 1929 M 4.9 Attica earthquake, however, the Clarenden–Linden fault system probably is capable of producing future M5 events. During this study, we reviewed newspaper accounts of the 1929 Attica earthquake, searched for earthquake-induced liquefaction features in sand and gravel pits and along tens of kilometers of river cutbanks, evaluated numerous soft-sediment deformation structures, compiled geotechnical data and performed liquefaction potential analysis of saturated sandy sediments. We found that the 1929 M 4.9 Attica earthquake probably did not induce liquefaction in its epicentral area and may have been generated by the western branch of the Clarendon–Linden fault system. Most soft-sediment deformation structures found during reconnaissance did not resemble earthquake-induced liquefaction features, and even the few that did could be attributed to non-seismic processes. Our analysis suggests that the magnitude threshold for liquefaction is between M 5.2 and 6, that a large (M≥6) earthquake would liquefy sediments at many sites in the area, and that a moderate earthquake (M 5–5.9) would liquefy sediments at some sites but perhaps not at enough sites to have been found during reconnaissance. We conclude that the Clarendon–Linden fault system could have produced small and moderate earthquakes, but probably not large events, during the Late Wisconsin and Holocene. 相似文献
2.
Martitia P. Tuttle 《Journal of Seismology》2001,5(3):361-380
A recent study in the New Madrid seismic zone demonstrates that large uncertainties, often involved but rarely expressed, in paleoliquefaction studies can be reduced by conducting detailed investigations at the most promising sites for dating liquefaction features. During the site investigations, care must be taken to collect samples that will provide close maximum and minimum dates for liquefaction features. It is advisable to use two-sigma calibrated dates, rather than one-sigma calibrated dates or radiocarbon ages, when estimating ages of liquefaction features. Well-constrained ages of individual liquefaction features should provide the basis for estimating the timing of paleoearthquakes and correlating features across a region. As uncertainty in ages of liquefaction features decreases, confidence in estimates of timing, source areas and magnitudes of paleoearthquakes increases. The New Madrid study also shows that modern or historic earthquakes that induced liquefaction in the same region and whose locations and magnitudes are fairly well know can serve as calibration events for paleoearthquakes. Future efforts that could further improve the usefulness of liquefaction feature in paleoseismology include (1) the development of new techniques for dating liquefaction features directly, (2) case studies of modern earthquakes that focus on the site and spatial distributions of liquefaction feature as well as geotechnical properties of liquefaction sites and (3) more rigorous quantification of uncertainties associated with estimates of timing, source areas and magnitudes of paleoearthquakes. 相似文献
3.
Weathering of the New Albany Shale, Kentucky: II. Redistribution of minor and trace elements 总被引：2，自引：1，他引：1
During weathering, elements enriched in black shale are dispersed in the environment by aqueous and mechanical transport. Here a unique evaluation of the differential release, transport, and fate of Fe and 15 trace elements during progressive weathering of the Devonian New Albany Shale in Kentucky is presented. Results of chemical analyses along a weathering profile (unweathered through progressively weathered shale to soil) describe the chemically distinct pathways of the trace elements and the rate that elements are transferred into the broader, local environment. Trace elements enriched in the unweathered shale are in massive or framboidal pyrite, minor sphalerite, CuS and NiS phases, organic matter and clay minerals. These phases are subject to varying degrees and rates of alteration along the profile. Cadmium, Co, Mn, Ni, and Zn are removed from weathered shale during sulfide-mineral oxidation and transported primarily in aqueous solution. The aqueous fluxes for these trace elements range from 0.1 g/ha/a (Cd) to 44 g/ha/a (Mn). When hydrologic and climatic conditions are favorable, solutions seep to surface exposures, evaporate, and form Fe-sulfate efflorescent salts rich in these elements. Elements that remain dissolved in the low pH (<4) streams and groundwater draining New Albany Shale watersheds become fixed by reactions that increase pH. Neutralization of the weathering solution in local streams results in elements being adsorbed and precipitated onto sediment surfaces, resulting in trace element anomalies.Other elements are strongly adsorbed or structurally bound to solid phases during weathering. Copper and U initially are concentrated in weathering solutions, but become fixed to modern plant litter in soil formed on New Albany Shale. Molybdenum, Pb, Sb, and Se are released from sulfide minerals and organic matter by oxidation and accumulate in Fe-oxyhydroxide clay coatings that concentrate in surface soil during illuviation. Chromium, Ti, and V are strongly correlated with clay abundance and considered to be in the structure of illitic clay. Illite undergoes minimal alteration during weathering and is concentrated during illuvial processes. Arsenic concentration increases across the weathering profile and is associated with the succession of secondary Fe(III) minerals that form with progressive weathering. Detrital fluxes of particle-bound trace elements range from 0.1 g/ha/a (Sb) to 8 g/ha/a (Mo). Although many of the elements are concentrated in the stream sediments, changes in pH and redox conditions along the sediment transport path could facilitate their release for aqueous transport. 相似文献
4.
The influence of solar‐induced thermal stresses on the mechanical weathering of rocks in humid mid‐latitudes 
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下载免费PDF全文 Jennifer Aldred Martha Cary Eppes Kimberly Aquino Rebecca Deal Jacob Garbini Suraj Swami Alea Tuttle George Xanthos 《地球表面变化过程与地形》2016,41(5):603-614
The role of solar‐induced thermal stresses in the mechanical breakdown of rock in humid‐temperate climates has remained relatively unexplored. In contrast, numerous studies have demonstrated that cracks in rocks found in more arid mid‐latitude locations exhibit preferred northeast orientations that are interpreted to be a consequence of insolation‐related cracking. Here we hypothesize that similar insolation‐related mechanisms may be efficacious in humid temperate climates, possibly in conjunction with other mechanical weathering processes. To test this hypothesis, we collected rock and crack data from a total of 310 rocks at a forested field site in North Carolina (99 rocks, 266 cracks) and at forested and unforested field sites in Pennsylvania (211 rocks, 664 cracks) in the eastern United States. We find that overall, measured cracks exhibit statistically preferred strike orientations (47° ± 16), as well as dip angles (52° ± 24°), that are similar in most respects to comparable datasets from mid‐latitude deserts. There is less variance in strike orientations for larger cracks suggesting that cracks with certain orientations are preferentially propagated through time. We propose that diurnally repeating geometries of solar‐related stresses result in propagation of those cracks whose orientations are favorably oriented with respect to those stresses. We hypothesize that the result is an oriented rock heterogeneity that acts as a zone of weakness much like bedding or foliation that can, in turn, be exploited by other weathering processes. Observed crack orientations vary somewhat by location, consistent with this hypothesis given the different latitude and solar exposure of the field sites. Crack densities vary between field sites and are generally higher on north‐facing boulder‐faces and in forested sites, suggesting that moisture‐availability also plays a role in dictating cracking rates. These data provide evidence that solar‐induced thermal stresses facilitate mechanical weathering in environments where other processes are also likely at play. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
5.
The current study provides long-term catch-rate, biological and feeding data for smooth hammerhead sharks, Sphyrna zygaena, caught in South Africa’s KwaZulu-Natal bather protection programme. In total, 2 512 S. zygaena were caught in net installations between 1978 and 2014, and 72 S. zygaena were caught on drumlines between 2007 and 2014. There was no significant log-linear year trend in the net catch rate over time (slope = 0.0054, t = 1.808, p = 0.07). However, there was a significant temporal increase in mean size of the captured sharks (slope = 0.0012, t = 3.502, p < 0.001). A quasi-Poisson generalised additive mixed model showed that increasing latitude, winter months, colder sea temperatures and the deployment of drumlines all had a significant positive effect on the catch rate of sharks in nets. The size frequency of the catch was unimodal, with significantly more females caught in the nets and more males on the drumlines. The majority (93.1%) of all sharks caught were immature and measured between 80 and 120 cm precaudal length. Teleosts and cephalopods dominated the sharks’ diet in terms of all dietary indices. The prey species consumed indicate that immature S. zygaena are feeding primarily within the pelagic zone of shallow coastal habitats. 相似文献
6.
There is mounting speculation that overharvesting of oyster stocks (Crassostrea virginica) in Chesapeake Bay may be a factor contributing to the decline in water quality and shifts in the dominance of species inhabiting the estuary. The trophic consequences of increasing the oyster population may be addressed using a simple quasi-equilibrium, mass action model of the exchanges transpiring in the Chesapeake mesohaline ecosystem. According to output from the model, increasing oyster abundance would decrease phytoplankton productivity as well as stocks of pelagic microbes, ctenophores, medusae, and particulate organic carbon. Recently acquired field data on phytoplankton productivity, bacterioplankton, and labile organic carbon in the vicinity of rafted oyster aquaculture support model predictions. The model also indicates that more oysters should increase benthic primary production, fish stocks, and mesozooplankton densities. Hence, augmenting the oyster community by restoring beds or introducing raft culture represents a potentially significant adjunct to the goal of mitigating eutrophication through curtailment of nutrient inputs. *** DIRECT SUPPORT *** A01BY059 00005 相似文献
7.
ML Camara B Mérigot F Leprieur JA Tomasini I Diallo M Diallo 《African Journal of Marine Science》2016,38(2):189-206
In a context of growing fishing pressures and recommendations for an ecosystem approach to fisheries, there is a need to monitor changes in fish communities over time. In this study, we analysed data from scientific trawl surveys carried out on the continental shelf off Guinea between 1985 and 2012. We performed factorial analyses and calculated biodiversity indices to characterise the changes in the structure and composition of fish communities that occurred over the 28-year period in this area, particularly given intensive fishing activities. We show that, over the study period, fish communities on the Guinean shelf were structured primarily according to spatial factors, with temporal changes being less pronounced than expected. However, a temporal analysis of biodiversity indices and species dominance showed that the intensification of fishing had significant effects on the general ecological features of the fish assemblages under study. There was a decrease in fish density and in mean trophic level. In addition, there were changes in species dominance, whereby large, slow-growing species with high commercial value were gradually replaced by smaller, fast-growing species of lesser commercial interest. These results from field observations are in line with some conclusions from previous modelling studies in the same geographical area, and provide further support for the hypothesis of a progressive ‘ecosystem effect of fishing’ occurring in Guinean waters. 相似文献
8.
Soil erosion and management recommendations at three State Vehicular Recreation areas,California 总被引：3，自引：0，他引：3
Off-road vehicle (ORV) impact on the landscape includes the destruction of protective vegetative cover, soil compaction, and
increased runoff followed by increased erosion. An investigation of three State Vehicular Recreation Areas (SVRAs) in arid
regions of California have documented 10-to 25-fold increases in sediment yield relative to nearby undisturbed basins. Soil
texture and slope length are the dominant factors controlling soil erodibility in these areas. Organic carbon content of the
soil exposed in hillclimb gullies was comparable to C horizon values of undisturbed soil profiles demonstrating a significant
(70%) loss of soil fertility due to accelerated erosion.
Soil erosion can be minimized and lifespan of these recreational areas prolonged by initiating and enforcing some critical
management policies, including careful control over location and length of hillclimb, rotating use areas such that rehabilitation
or revegetation is feasible, and seasonal use restrictions. 相似文献
9.
JD Klein AE Bester-van der Merwe ML Dicken A Emami-Khoyi KL Mmonwa 《African Journal of Marine Science》2019,41(1):115-118
Genomic data can be a useful tool in the management and conservation of biodiversity. Here, we report the development of genomic resources for the spotted ragged-tooth shark Carcharias taurus using genome-wide DNA data from Illumina next-generation sequencing. We explored two commonly used genetic marker types: microsatellites and mitochondrial DNA. A total of 4 394 putative microsatellites were identified, of which 10 were tested on 24 individuals and found to have ideal properties for population genetic analyses. Additionally, we reconstructed the first complete mitochondrial genome of a South African spotted ragged-tooth shark, and highlight the most informative gene regions to facilitate future primer design. The data reported here may serve as a resource for future studies and can ultimately be applied in the sustainable conservation and fisheries management of this apex predator. 相似文献
10.
When the earth blisters: Exploring recurrent liquefaction features in the coastal system of Christchurch,New Zealand 下载免费PDF全文
下载免费PDF全文 Monica Giona Bucci Peter Almond Pilar Villamor William Ries Carol Smith Martitia Tuttle 《地学学报》2017,29(3):162-172
The 14 February, or Valentine's Day, 2016 earthquake located offshore of Christchurch produced a new generation of liquefaction in the coastal environment of Christchurch, an environment of recurrent liquefaction during the 2010–2011 Canterbury Earthquake Sequence. The Valentine's Day earthquake occurred while trenches were open at a site in the coastal environment for studying the 2010–2011 liquefaction features. Observations in the 2016 trenches provided insights into the formation of a suite of surface and subsurface liquefaction features characteristic of the dune deposits, related to the persistent shallow water table, well‐sorted sands within the liquefiable layer and the soil above. Given these conducive conditions, there is a high potential that all earthquakes capable of inducing liquefaction may have been recorded during formation of the dunes near Christchurch. However, overprinting by subsequent generations of liquefaction features may be common and present challenges in unravelling the event history. 相似文献