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1.
Microseismic noise was studied in the frequency range 0.5–30 Hz in the conditions prevailing in the town of Vorkuta. A seismic
noise model was developed consisting of power spectral densities of ground motion velocity separately for daytime and nighttime
in different frequency ranges. The absolute noise level for frequencies of 1–5 Hz in Vorkuta varies between −140 and −150
dB in daytime and from −152 to −158 dB in nighttime, with the ranges for the 8-15 Hz noise being −140 to −155 dB in daytime
and −155 to −165 dB in nighttime. Well-pronounced daily variations in noise amplitude were observed in the frequency ranges
1.5–3 Hz and 14–17 Hz. The noise amplitude varies by 7 dB over 24 hours, with the amplitude of horizontal component variation
being 5 dB above that of the vertical component. The power spectral densities of ground motion velocity in the microseismic
noise involve several spectral peaks, whose central frequencies did not vary by more than 0.15 Hz during the entire period
of instrumental observation. The seismic background in the town of Vorkuta contains seismic events due to distant earthquakes
and local industrial explosions. 相似文献
2.
Katrina J. Butkas Yvonne Vadeboncoeur M. Jake Vander Zanden 《Aquatic Sciences - Research Across Boundaries》2011,73(1):153-169
Studies of aquatic invertebrate production have been primarily conducted at the level of individual taxa or populations. Advancing
our understanding of the functioning and energy flow in aquatic ecosystems necessitates scaling-up to community and whole-lake
levels, as well as integrating across benthic and pelagic habitats and across multiple trophic levels. In this paper, we compare
a suite of non-cohort based methods for estimating benthic invertebrate production at subpopulation, habitat, and whole-lake
levels for Sparkling Lake, WI, USA. Estimates of the overall mean benthic invertebrate production (i.e. whole-lake level)
ranged from 1.9 to 5.0 g DM m−2 y−1, depending on the method. Production estimates varied widely among depths and habitats, and there was general qualitative
agreement among methods with regards to differences in production among habitats. However, there were also consistent and
systematic differences among methods. The size-frequency method gave the highest, while the regression model of Banse and
Mosher (Ecol Monogr 50:355–379, 1980) gave the lowest production estimates. The regression model of Plante and Downing (Can J Fish Aquat Sci 46:1489–1498, 1989) had the lowest average coefficients of variation at habitat (CV = 0.17) and whole-lake (CV = 0.08) levels. At the habitat
level, variance in production estimates decreased with sampling effort, with little improvement after 10–15 samples. Our study
shows how different production estimates can be generated from the same field data, though aggregating estimates up to the
whole-lake level does produce an averaging effect that tends to reduce variance. 相似文献
3.
R. Puglia R. Ditommaso F. Pacor M. Mucciarelli L. Luzi M. Bianca 《Bulletin of Earthquake Engineering》2011,9(3):869-892
Previous works based mainly on strong-motion recordings of large Japanese earthquakes showed that site amplification and soil
fundamental frequency could vary over long and short time scales. These phenomena were attributed to non-linear soil behaviour:
the starting fundamental frequency and amplification were both instantaneously decreasing and then recovering for a time varying
from few seconds to several months. The recent April 6, 2009 earthquake (M
W 6.3), occurred in the L’Aquila district (central Italy), gave us the possibility to test hypotheses on time variation of
amplification function and soil fundamental frequency, thanks to the recordings provided by a pre-existing strong-motion array
and by a large number of temporary stations. We investigated the intra- and inter-event soil frequency variations through
different spectral analyses, including time-frequency spectral ratios and S-Transform (Stockwell et al. in IEEE Trans Signal
Process 44:998–1001, 1996). Finally, analyses on noise recordings were performed, in order to study the soil behaviour in linear conditions. The results
provided puzzling evidences. Concerning the long time scale, little variation was observed at the permanent stations of the
Aterno Valley array. As for the short time-scale variation, the evidence was often contrasting, with some station showing
a time-varying behavior, while others did not change their frequency with respect to the one evaluated from noise measurements.
Even when a time-varying fundamental frequency was observed, it was difficult to attribute it to a classical, softening non-linear
behaviour. Even for the strongest recorded shocks, with peak ground acceleration reaching 0.7 g, variations in frequency and
amplitude seems not relevant from building design standpoint. The only exception seems to be the site named AQV, where the
analyses evidence a fundamental frequency of the soil shifting from 3 Hz to about 1.5 Hz during the mainshock. 相似文献
4.
Use of spectral acceleration data for determination of three-dimensional attenuation structure in the Pithoragarh region of Kumaon Himalaya 总被引:1,自引:0,他引:1
Three-dimensional attenuation structures are related to the subsurface heterogeneities present in the earth crust. An algorithm
for estimation of three-dimensional attenuation structure in the part of Garhwal Himalaya, India has been presented by Joshi
(Curr Sci 90:581–585, 2006b; Nat Hazards 43:129–146, 2007). In continuation of our earlier approach, we have presented a method in which strong motion data have been used to estimate
frequency-dependent three-dimensional attenuation structure of the region. The border district of Pithoragarh in the Higher
Himalaya, India, lies in the central seismic gap region of Himalaya. This region falls in the seismic zones IV and V of the
seismic zoning map of India. A dense network consisting of eight accelerographs has been installed in this region. This network
has recorded several local events. An algorithm based on inversion of strong motion digital data is developed in this paper
to estimate attenuation structure at different frequencies using the data recorded by this network. Twenty strong motion records
observed at five stations have been used to estimate the site amplification factors using inversion algorithm defined in this
paper. Site effects obtained from inversion has been compared with that obtained using Nakamura (1988) and Lermo et al. (Bull Seis Soc Am 83:1574–1594, 1993) approach. The obtained site amplification term has been used for correcting spectral acceleration data at different stations.
The corrected spectral acceleration data have been used as an input to the developed algorithm to avoid effect of near-site
soil amplification term. The attenuation structure is estimated by dividing the entire area in several three-dimensional block
of different frequency-dependent shear wave quality factor Q
β
(f). The input to this algorithm is the spectral acceleration of S phase of the corrected accelerogram. The outcome of the algorithm
is given in terms of attenuation coefficient and source acceleration spectra. In the present study, this region has been divided
into 25 rectangular blocks with thickness of 10 km and surface dimension of 12.5 × 12.1 km, respectively. Present study gives
three-dimensional attenuation model of the region which can be used for both hazard estimation and simulation of strong ground
motion. 相似文献
5.
The effect of horizontal grid resolution on the horizontal relative dispersion of particle pairs has been investigated on
a short time scale, i.e. one tidal M
2 cycle. Of particular interest is the tidal effect on dispersion and transports in coastal waters where small-scale flow features
are important. A three-dimensional ocean model has been applied to simulate the tidal flow through the Moskstraumen Maelstrom
outside Lofoten in northern Norway, well known for its strong current and whirlpools (Gjevik et al., Nature 388(6645):837–838,
1997; Moe et al., Cont Shelf Res 22(3):485–504, 2002). Simulations with spatial resolution down to 50 m have been carried out. Lagrangian tracers were passively advected with
the flow, and Lyapunov exponents and power law exponents have been calculated to analyse the separation statistics. It is
found that the relative dispersion of particles on a short time scale (12–24 h) is very sensitive to the grid size and that
the spatial variability is also very large, ranging from 0 to 100 km2 over a distance of 100 m. This means that models for prediction of transport and dispersion of oil spills, fish eggs, sea
lice etc. using a single diffusion coefficient will be of limited value, unless the models actually resolves the small-scale
eddies of the tidal current. 相似文献
6.
Marcos E. C. Bernardes Mark A. Davidson Keith R. Dyer Ken J. George 《Ocean Dynamics》2006,56(3-4):186-197
The main objective of this paper is to address the principal mechanisms involved in the medium-term (order of months to years) morphodynamic evolution of estuaries through the application of a process-based numerical modelling. The Teign estuary (Teignmouth, UK) is the selected site. The system is forced by the macrotidal semi-diurnal tide in the English Channel and is perturbed to a minor extent by high river discharge events (freshets). Although waves have a definite influence on the adjacent coastal area, Wells (Teignmouth Quay Development Environmental Statement: Changes to Physical Processes. Report R.984c:140. ABP Marine Environmental Research Ltd., Southampton, 2002b) suggested that swell waves do not enter the estuary. Hence, wave effects are neglected in this study, as only tides and the river discharge are taken into account. The sediment grain size is highly variable, but mainly sandy. Within the frame of the COAST3D project (), four bathymetric surveys of the adjacent coastal area were carried out at a nearly weekly intervals. The outer estuary and the adjacent coastal area were also surveyed every 6 months as part of the COASTVIEW project (). Based on these data and on continuously measured parameters, such as water level, waves, wind and river discharge, numerical modelling of the morphodynamic processes can be tested. To replicate the morphological changes in the medium-term within a feasible simulation time, forcing conditions are reduced through the use of an input reduction method (called ensemble technique). In this study, simulations are based on the coupling between Telemac-2D and its non-cohesive sediment transport module, Sisyphe (version 5.3 for both modules). Three different sediment transport formulae were tested: (1) Engelund and Hansen (A monograph on sediment transport in alluvial streams, 3rd edn. Technological University of Denmark, Copenhagen, 1967) including the modifications proposed by Chollet and Cunge (J Hydraul Eng 17(1):1–13, 1979); (2) Bijker (Mechanics of sediment transport by the combination of waves and current. In: Design and reliability of coastal structures. 23rd international conference on Coastal Engineering, pp 147–173, 1968) and (3) Soulsby (Dynamics of Marine Sands. A manual for practical applications. HR Wallingford, Wallingford, p 142, 1997) modified version of van Rijn [J Hydraul Eng 110(10):1431–1456, 1984a, J Hydraul Eng 110(11):1613–1641, 1984b] formulation. Both a qualitative (i.e. visual comparison) and a quantitative tool [Brier Skill Score (BSS); described in Sutherland et al. in Coast Eng 51:917–939, 2004b] are applied to assess the similarity of simulations when compared to model predictions and observations. Tests confirmed the reliability and time efficiency of the ensemble technique, since it reproduced very well the results of a reference run, a computation based on the observed boundary conditions. For the spring-neap cycle modelled, the BSS was of 0.91 (a perfect modelling would have a BSS of 1), with a reduction in the simulation time on the order of 80%. For the 6-month-period simulation, results were also excellent: BSS=0.92 and a computer time reduction of 85%. In principle, this method has the advantage of being applied to any process-based numerical model. 相似文献
7.
A reappraisal of shear wave splitting parameters from Italian active volcanic areas through a semiautomatic algorithm 总被引:1,自引:0,他引:1
Shear wave splitting parameters represent a useful tool to detail the stress changes occurring in volcanic environments before
impending eruptions. In the present paper, we display the parameter estimates obtained through implementation of a semiautomatic
algorithm applied to all useful datasets of the following Italian active volcanic areas: Mt. Vesuvius, Campi Flegrei, and
Mt. Etna. Most of these datasets have been the object of several studies (Bianco et al., Annali di Geofisica, XXXXIX 2:429–443,
1996, J Volcanol Geotherm Res 82:199–218, 1998a, Geophys Res Lett 25(10):1545–1548, 1998b, Phys Chem Earth 24:977–983, 1999, J Volcanol Geotherm Res 133:229–246, 2004, Geophys J Int 167(2):959–967, 2006; Del Pezzo et al., Bull Seismol Soc Am 94(2):439–452, 2004). Applying the semiautomatic algorithm, we confirmed the results obtained in previous studies, so we do not discuss in much
detail each of our findings but give a general overview of the anisotropic features of the investigated Italian volcanoes.
In order to make a comparison among the different volcanic areas, we present our results in terms of the main direction of
the fast polarization (φ) and percentage of shear wave anisotropy (ξ). 相似文献
8.
An automatic scheme for baseline correction of strong-motion records in coseismic deformation determination 总被引:2,自引:0,他引:2
Coseismic deformation can be determined from strong-motion records of large earthquakes. Iwan et al. (Bull Seismol Soc Am
75:1225–1246, 1985) showed that baseline corrections are often required to obtain reliable coseismic deformation because baseline offsets lead
to unrealistic permanent displacements. Boore (Bull Seismol Soc Am 91:1199–1211, 2001) demonstrated that different choices of time points for baseline correction can yield realistically looking displacements,
but with variable amplitudes. The baseline correction procedure of Wu and Wu (J Seismol 11:159–170, 2007) improved upon Iwan et al. (Bull Seismol Soc Am 75:1225–1246, 1985) and achieved stable results. However, their time points for baseline correction were chosen by a recursive process with
an artificial criterion. In this study, we follow the procedure of Wu and Wu (J Seismol 11:159–170, 2007) but use the ratio of energy distribution in accelerograms as the criterion to determine the time points of baseline correction
automatically, thus avoiding the manual choice of time points and speeding up the estimation of coseismic deformation. We
use the 1999 Chi-Chi earthquake in central Taiwan and the 2003 Chengkung and 2006 Taitung earthquakes in eastern Taiwan to
illustrate this new approach. Comparison between the results from this and previous studies shows that our new procedure is
suitable for quick and reliable determination of coseismic deformation from strong-motion records. 相似文献
9.
Decadal evolution of a degassing magma reservoir unravelled from fire fountains produced at Etna volcano (Italy) between 1989 and 2001 总被引:1,自引:1,他引:0
Between 1989 and 2001, five eruptions at Etna displayed a regular alternation between repose periods and episodes rich in
gas, termed quasi-fire fountains and consisting of a series of Strombolian explosions sometimes leading to a fire fountain.
This behaviour results from the coalescence of a foam layer trapped at the top of the reservoir which was periodically rebuilt
prior to each episode (Vergniolle and Jaupart, J Geophys Res 95:2793–2809, 1990). Visual observations of fire fountains are combined with the foam dynamics to estimate the five degassing parameters characteristic
of the degassing reservoir, i.e. the number of bubbles, gas volume fraction, bubble diameter, reservoir thickness and reservoir
volume. The study of decadal cycles of eruptive patterns (Allard et al., Earth Sci Rev 78:85–114, 2006) suggests that the first eruption with fire fountains occurred in 1995 while the last one happened in 2001. The number of
bubbles and the gas volume fraction increase smoothly from the beginning of the cycle (1995) to its end (2001). The increasing
number of bubbles per cubic metre, from 0.61–20×105 to 0.1–3.4×109, results from cooling of the magma within the reservoir. The simultaneously decreasing bubble diameter, from 0.67–0.43 to
0.30–0.19 mm, is related to the decreasing amount of dissolved volatiles. Meanwhile, the thickness and the volume of the degassing
reservoir diminish, from values typical of the magma reservoir to values characteristic of a very thin bubbly layer, marking
the quasi-exhaustion of volatiles. The magma reservoir has a slender vertical shape, with a maximum thickness of 3,300–8,200 m
and a radius of 240 m (Vergniolle 2008), making its detection from seismic studies difficult. Its volume, at most 0.58–1.4 km3, is in agreement with geochemical studies (0.5 km3) (Le Cloarec and Pennisi, J Volcanol Geotherm Res 108:141–155, 2001). The time evolution of both the total gas volume expelled per eruption, and the inter-eruptive gas flux results from the
competition between the increasing number of bubbles and the decreasing bubble diameter. The smooth temporal evolution of
the five degassing parameters also points towards bubbles being produced by a self-induced mechanism within the magma reservoir
rather than by a magmatic reinjection prior to each eruption. The decadal cycles are therefore initiated by a magmatic reinjection,
in agreement with a typical return time of 14–80 years (Albarède 1993). Hence, the 1995 eruption results from a fresh magma being newly emplaced while the magma from the following eruptions is
progressively depleted in volatiles species until reaching a state of quasi-exhaustion in 2001. A magmatic reinjection of
0.13–0.6 km3 every few decades is sufficient to explain the expelled gas volume, including SO2. A scenario is also proposed for the alternation between gas-rich summit eruptions and gas-poor flank eruptions which are
observed during decadal cycles. The scenario proposed for Etna could also be at work at Piton de la Fournaise and Erta ’Ale
volcanoes. 相似文献
10.
Abiotic effects of UV on planktonic P kinetics 总被引:1,自引:0,他引:1
Jeff M. Sereda Jeff J. Hudson William D. Taylor 《Aquatic Sciences - Research Across Boundaries》2009,71(2):127-134
11.
Liverpool Bay is a region of freshwater influence which receives significant freshwater loading from a number of major English
and Welsh rivers. Strong tidal current flow interacts with a persistent freshwater-induced horizontal density gradient to
produce strain-induced periodic stratification (SIPS). Recent work (Palmer in Ocean Dyn 60:219–226, 2010; Verspecht et al. in Geophys Res Lett 37:L18602, 2010) has identified significant modification to tidal ellipses in Liverpool Bay during stratification due to an associated reduction
in pycnocline eddy viscosity. Palmer (Ocean Dyn 60:219–226, 2010) identified that this modification results in asymmetry in flow in the upper and lower layers capable of permanently transporting
freshwater away from the Welsh coastline via a SIPS pumping mechanism. Observational data from a new set of observations from
the Irish Sea Observatory site B confirm these results; the measured residual flow is 4.0 cm s−1 to the north in the surface mixed layer and 2.4 cm s−1 to the south in the bottom mixed layer. A realistically forced 3D hydrodynamic ocean model POLCOMS succeeds in reproducing
many of the characteristics of flow and vertical density structure at site B and is used to estimate the transport of water
through a transect WT that runs parallel with the Welsh coast. Model results show that SIPS is the dominant steady state,
occurring for 78.2% of the time whilst enduring stratification exists only 21.0% of the year and enduring mixed periods, <1%.
SIPS produces a persistent offshore flow of freshened surface water throughout the year. The estimated net flux of water in
the surface mixed layer is 327 km3 year
−1, of which 281 km3 year−1 is attributable to SIPS periods. Whilst the freshwater component of this flux is small, the net flux of freshwater through
WT during SIPS is significant, the model estimates 1.69 km3 year−1 of freshwater to be transported away from the coast attributable to SIPS periods equivalent to 23% of annual average river
flow from the four catchment areas feeding Liverpool Bay. The results show SIPS pumping to be an important process in determining
the fate of freshwater and associated loads entering Liverpool Bay. 相似文献
12.
We address possibilities of minimising environmental risks using statistical features of current-driven propagation of adverse
impacts to the coast. The recently introduced method for finding the optimum locations of potentially dangerous activities
(Soomere et al. in Proc Estonian Acad Sci 59:156–165, 2010) is expanded towards accounting for the spatial distributions of probabilities and times for reaching the coast for passively
advecting particles released in different sea areas. These distributions are calculated using large sets of Lagrangian trajectories
found from Eulerian velocity fields provided by the Rossby Centre Ocean Model with a horizontal resolution of 2 nautical miles
for 1987–1991. The test area is the Gulf of Finland in the northeastern Baltic Sea. The potential gain using the optimum fairways
from the Baltic Proper to the eastern part of the gulf is an up to 44% decrease in the probability of coastal pollution and
a similar increase in the average time for reaching the coast. The optimum fairways are mostly located to the north of the
gulf axis (by 2–8 km on average) and meander substantially in some sections. The robustness of this approach is quantified
as the typical root mean square deviation (6–16 km) between the optimum fairways specified from different criteria. Drastic
variations in the width of the ‘corridors’ for almost optimal fairways (2–30 km for the average width of 15 km) signifies
that the sensitivity of the results with respect to small changes in the environmental criteria largely varies in different
parts of the gulf. 相似文献
13.
A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity
are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year
study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA)
and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during
the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed
in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO
x
decreased by 25 ± 4 μmol kg−1 and DIC by 106 ± 16 μmol kg−1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of
TA increased by 33 ± 8 μmol kg−1 (2009) and 33 ± 15 μmol kg−1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al.
(2009) suggested that denitrification may enhance the CO2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it
does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake
of CO2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow
are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot
be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show
that patterns of seasonal change in concentrations of TA in river inputs differ between river systems. 相似文献
14.
Lee E. Brown Alexander M. Milner David M. Hannah 《Aquatic Sciences - Research Across Boundaries》2010,72(3):325-334
Glacier retreat and thinning are occurring in many regions of the world, leading to significant changes in river discharge,
water quality and aquatic ecosystems. Therefore, it is increasingly necessary for environmental scientists and managers to
develop and adopt methods that link changes in meltwater dynamics and biotic response to better understand and predict future
ecosystem change in glacially influenced rivers. To this end, two approaches have been developed recently: (1) the ARISE quantitative
meltwater contribution approach of Brown et al. (Freshw Biol 54:1357–1369, 2009b) and (2) the glaciality index (GI) of Ilg and Castella (Freshw Biol 51:840–853, 2006), which provides a measure of glacial runoff influence on stream ecosystems based on four environmental variables (water
temperature, channel stability, electrical conductivity and suspended sediment concentration). However, the relative performance
and potential complementarities of these two approaches have yet to be evaluated. We conducted a methodological comparison
using detailed hydrological, water quality and biological datasets collected over two summers in the French Pyrénées. Analyses
revealed strong and significant correlation between ARISE meltwater contributions and the GI. However, the ARISE approach
performed better when differentiating glacial influence between streams and over time. Both approaches were significant predictors
of macroinvertebrate taxonomic richness, beta diversity, the number of EPT genera and total abundance, although regression
models were typically stronger for the ARISE meltwater contribution approach. At the species level, ARISE performed better
for predicting the abundance of 13 of the 20 most common taxa. We propose both approaches are valuable for assessing the effects
of decreasing meltwater contributions on river ecosystems at the community level but this case study suggests ARISE was better
able to identify subtle differences in hydrological change, community response and the abundance of individual taxa. Comparative
studies from other catchments are required to further evaluate the two methods. 相似文献
15.
G. A. Mikhailova Yu. M. Mikhailov O. V. Kapustina S. E. Smirnov 《Geomagnetism and Aeronomy》2010,50(6):814-823
We have performed a spectral analysis of variations in the E
z
component of a quasistatic electric field in the atmospheric surface layer in a wide band of internal gravity waves (from
5 min to 3 h) for quiet and seismically active conditions as well as high thunderstorm activity. Observational data of the
field for September, 1999 and August–September, 2002, were used. It has been shown that, if there are no thunderstorms or
earthquakes, the background spectrum includes oscillations with maxima at periods of T ∼ 1.8 and 1 h, 40, 30, 15, and 10–13 min. Their intensity in the range of periods of 0.5–3.0 h is two or more orders of magnitude
higher than the intensity of maxima in the range of 5–30 min. Before earthquakes, with anomalies in diurnal variations of
field intensity, there is a tendency of increased background spectrum at maxima noted there. In both ranges of oscillation
periods, the spectral intensity increases by one to one and a half orders of magnitude. Under high thunderstorm activity,
the variability is higher as compared to the spectra of earthquake precursors by both locations of maxima and their intensity.
The intensity of maxima exceeds the maxima on the eve of earthquakes one to one and a half orders of magnitude in the range
of periods 0.5–3.0 h and two and more orders of magnitude in the range of periods 5–30 min. 相似文献
16.
17.
John E. Hathaway Richard O. Gilbert John E. Wilson Brent A. Pulsipher 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(2):253-261
After site clean-up teams have removed all of what they believe to be UXO within a specific impact area, statistical compliance
sampling is a possible method for verifying with a specified probability that this area has been cleaned to specifications.
Schilling [J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] developed a compliance sampling methodology based on the hypergeometric distribution. Bowen and Bennett (1987) also use compliance sampling where they provide an approximation for estimating the number of samples (n) required to state with desired probability that the entire population of sample units (N, where n < N) are in compliance with cleanup goals. This article describes two methods (anomaly and transect) for applying the Schilling
[J Qual Technol 10(2):47–51, 1978, Acceptance sampling in quality control. Marcel Dekker, Inc., New York, 1982] compliance sampling method to military training sites. After describing these methods, a simulation study is presented which
demonstrates the performance of transect compliance sampling calculations based on varied degrees of clustered UXO within
a specific impact area and different types of sampling routines. 相似文献
18.
In this work we present and discuss the results of ambient seismic noise analyses computed at four sites where seismic stations,
managed by the INGV (Italian Institute for Geophysics and Vulcanology) and the DPC (Italian Department of Civil Protection), are installed inside buildings. The experiments were performed considering different types of installation: sensor located
at the bottom of a school, directly installed on rock (case 1); sensor located at the bottom of a medieval fortress, built
on an isolate hill, directly installed on rock (case 2); sensor installed on the foundations of a medieval fortress, built
on an isolate hill (case 3); sensor installed on the foundations of a school, built on alluvial deposits (case 4). Since recent
works proposed the use of spectral ratio techniques to study the dynamic characterization of buildings, ambient seismic-noise
measurements were performed for each site close to the stations (at the base of the structures), at the top of the structures
and outside the buildings. In order to check the source of vibrations both horizontal to vertical spectral ratio (HVNR) and
standard spectral ratio (SSR) techniques were applied. For all stations the results from ambient seismic noise were compared
to those obtained from earthquakes (HVSR). In order to detect preferential directions of amplification, for each site average
HVNRs and HVSRs were computed considering one azimuth for each set of 5°. We obtain different results for different types
of installation: in cases 1 and 2, where the sensors are directly installed on rock, the vibrations of the structure do not
affect the noise measures performed close to the stations, which show flat HVNR in the whole frequency range: in both cases
the eigenfrequency of the building is given by the HVNR calculated from the measures performed at the top of the structure.
In cases 3 and 4, where the sensors are installed on the foundations of the considered structures, both the amplification
peaks between 5 and 9 Hz (case 3) and between 5.5 and 7 Hz (case 4) include the contribution of the free oscillations of the
buildings. In particular, in case 4, HVNRs performed outside building highlight possible soil–structure resonance effects
in case of an earthquake. 相似文献
19.
Mohamed A. Gamal 《Journal of Seismology》2009,13(1):13-30
In order to determine the fundamental period of soil vibrations in Cairo, 174 microtremors stations, in conjunction with mobile
accelerographs, were used. The result was a collection of long-period microtremors and ambient noise arising from cultural
disturbances. The Nile Valley shows some fixed peaks at 2.5–3.5 Hz at the center of the basin, while the Nile’s surrounding
area shows a fundamental peak of 4–5 Hz, leaving a 5–7-Hz resonance peak for the sand-like, gravelly soil from Abbasiya to
the airport. A frequency-dependent soil amplification map is drawn, which includes seismic microzonation maps for Cairo. Based
on the above, a maximum acceleration map for two important earthquakes affecting Egypt in the last century is produced (Faiyum,
1992, and Aqaba, 1995). 相似文献