scholarly journals On the point-source approximation of earthquake dynamics

2014 ◽  
Vol 57 (3) ◽  
Author(s):  
Andrea Bizzarri
Keyword(s):  
Point Source ◽  
Seismic Waves ◽  
Single Point ◽  
Seismic Source ◽  
Transition Process ◽  
Point Sources ◽  
Multiple Point ◽  
Earthquake Dynamics ◽  
Planar Fault ◽  
Source Models

<p>The focus on the present study is on the point-source approximation of a seismic source. First, we compare the synthetic motions on the free surface resulting from different analytical evolutions of the seismic source (the Gabor signal (G), the Bouchon ramp (B), the Cotton and Campillo ramp (CC), the Yoffe function (Y) and the Liu and Archuleta function (LA)). Our numerical experiments indicate that the CC and the Y functions produce synthetics with larger oscillations and correspondingly they have a higher frequency content. Moreover, the CC and the Y functions tend to produce higher peaks in the ground velocity (roughly of a factor of two). We have also found that the falloff at high frequencies is quite different: it roughly follows ω<span><sup>−2</sup></span> in the case of G and LA functions, it decays more faster than ω<span><sup>−2</sup></span> for the B function, while it is slow than ω<span><sup>−1</sup></span> for both the CC and the Y solutions. Then we perform a comparison of seismic waves resulting from 3-D extended ruptures (both supershear and subshear) obeying to different governing laws against those from a single point-source having the same features. It is shown that the point-source models tend to overestimate the ground motions and that they completely miss the Mach fronts emerging from the supershear transition process. When we compare the extended fault solutions against a multiple point-sources model the agreement becomes more significant, although relevant discrepancies still persist. Our results confirm that, and more importantly quantify how, the point-source approximation is unable to adequately describe the radiation emitted during a real world earthquake, even in the most idealized case of planar fault with homogeneous properties and embedded in a homogeneous, perfectly elastic medium.</p>

An inversion technique for the retrieval of single-point emissions from atmospheric concentration measurements

2009 ◽  
Vol 465 (2107) ◽  
pp. 2069-2088 ◽  
Author(s):  
Maithili Sharan ◽  
Jean-Pierre Issartel ◽  
Sarvesh Kumar Singh ◽  
Pramod Kumar
Keyword(s):  
Point Source ◽  
Dispersion Model ◽  
Single Point ◽  
Point Sources ◽  
Average Error ◽  
Diffusion Experiment ◽  
Theoretical Point ◽  
Monitoring Networks ◽  
Atmospheric Concentration ◽  
Concentration Measurements

The aim of the study is to propose a technique for the retrieval of point sources of atmospheric trace species from concentration measurements. The inverse problem of identifying the parameters of a point source is addressed within the assimilative framework of renormalization recently proposed for the identification of distributed emissions. This theory has been extended for the point sources based on the property that these are associated with the maximum of the renormalized estimate computed from the observations. This approach along with an analytic dispersion model is used for point source identification, and the sensitivity of the samplers is described by the same model in backward mode. The proposed technique is illustrated not only with synthetic measurements but also with seven sets of observations, corresponding to convective conditions, taken from the low-wind tracer diffusion experiment conducted at the Indian Institute of Technology Delhi in 1991. The position and intensity of the source are retrieved exactly with the synthetic measurements in all the sets validating the technique. The position of the source is retrieved with an average error of 17 m, mostly along wind; its intensity is estimated within a factor 2 for all the sets of real observations. From a theoretical point of view, the link established between point and distributed sources clarifies new concepts for the exploitation of monitoring networks. In particular, the influence of the noise on the identification of a source is related to the relative visibility of the various regions described with a renormalizing weight function. The geometry of the environment modified according to the weights is interpreted as an apparent geometry. It is analogous to the apparent flatness of the starry sky in eye's view, usually considered an impression rather than a scientific fact.

scholarly journals The nature of point source fringes in mid-infrared spectra acquired with the James Webb Space Telescope

2020 ◽  
Vol 641 ◽  
pp. A150 ◽  
Author(s):  
Ioannis Argyriou ◽  
Martyn Wells ◽  
Alistair Glasse ◽  
David Lee ◽  
Pierre Royer ◽  
...  
Keyword(s):  
Point Source ◽  
Point Spread Function ◽  
Point Sources ◽  
Systematic Variation ◽  
Multiple Point ◽  
Mid Infrared ◽  
Space Telescope ◽  
Point Spread ◽  
Spread Function ◽  
Extended Sources

Context. As is common for infrared spectrometers, the constructive and destructive interference in different layers of the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) detector arrays modulate the detected signal as a function of wavelength. The resulting “fringing” in the Medium-Resolution Spectrometer (MRS) spectra varies in amplitude between 10% and 30% of the spectral baseline. A common method for correcting for fringes relies on dividing the data by a fringe flat. In the case of MIRI MRS, the fringe flat is derived from measurements of an extended, spatially homogeneous source acquired during the thermal-vacuum ground verification of the instrument. While this approach reduces fringe amplitudes of extended sources below the percent level, at the detector level, point source fringe residuals vary in a systematic way across the point spread function. The effect could hamper the scientific interpretation of MRS observations of unresolved sources, semi-extended sources, and point sources in crowded fields. Aims. We find MIRI MRS point source fringes to be reproducible under similar observing conditions. We want to investigate whether a generic and accurate correction can be determined. Therefore, we want to identify the variables, if they exist, that would allow for a parametrization of the signal variations induced by point source fringe modulations. Methods. We determine the point source fringe properties by analyzing MRS detector plane images acquired on the ground. We extracted the fringe profile of multiple point source observations and studied the amplitude and phase of the fringes as a function of field position and pixel sampling of the point spread function of the optical chain. Results. A systematic variation in the amplitude and phase of the point source fringes is found over the wavelength range covered by the test sources (4.9 − 5.8 μm). The variation depends on the fraction of the point spread function seen by the detector pixel. We identify the non-uniform pixel illumination as the root cause of the reported systematic variation. This new finding allows us to reconcile the point source and extended source fringe patterns observed in test data during ground verification. We report an improvement after correction of 50% on the 1σ standard deviation of the spectral continuum. A 50% improvement is also reported in line sensitivity for a benchmark test with a spectral continuum of 100 mJy. The improvement in the shape of weak lines is illustrated using a T Tauri model spectrum. Consequently, we verify that fringes of extended sources and potentially semi-extended sources and crowded fields can be simulated by combining multiple point source fringe transmissions. Furthermore, we discuss the applicability of this novel fringe-correction method to the MRS data (and the data of other instruments).

FIELD RELEASES OF TRICHOGRAMMA MINUTUM (HYMENOPTERA: TRICHOGRAMMATIDAE) FOR SUPPRESSION OF EPIDEMIC SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (LEPIDOPTERA: TORTRICIDAE), EGG POPULATIONS IN MAINE

1984 ◽  
Vol 116 (10) ◽  
pp. 1357-1366 ◽  
Author(s):  
Mark W. Houseweart ◽  
Daniel T. Jennings ◽  
Robert K. Lawrence
Keyword(s):  
Point Source ◽  
Choristoneura Fumiferana ◽  
Single Point ◽  
Spruce Budworm ◽  
Point Sources ◽  
Slight Improvement ◽  
Parasitism Rates ◽  
Trichogramma Minutum ◽  
Multiple Releases ◽  
Better Than

AbstractTrichogramma minutum Riley was released in the field for suppression of epidemic spruce budworm, Choristoneura fumiferana (Clemens), egg populations in Maine from 1977 to 1981. Commercially reared California-strain T. minutum were released from the ground at single-point sources in 1977. In 1978, using 4-point-source releases, we found that the native Maine-strain performed better than the California strain. In 1979, broadcast and multiple releases from the ground gave slight improvement in parasitism over 4-point releases. In 1981, three closely timed, aerially broadcast releases from a helicopter yielded increases in parasitism rates significantly higher than those in control plots, but not sufficient to suppress epidemic spruce budworm populations. Important variables and suggestions for future aerial releases are discussed.

Sources of Nitrogen and Phosphorus in the Catchment Area of Neusiedlersee/Fertö, Austria/Hungary

1993 ◽  
Vol 28 (3-5) ◽  
pp. 101-110 ◽  
Author(s):  
W. v. d. Emde ◽  
H. Fleckseder ◽  
N. Matsché ◽  
F. Plahl-Wabnegg ◽  
G. Spatzierer ◽  
...  
Keyword(s):  
Point Source ◽  
Catchment Area ◽  
Management Practice ◽  
Water Erosion ◽  
Nonpoint Source ◽  
Point Sources ◽  
Source Control ◽  
Nitrogen And Phosphorus ◽  
Catchment Areas ◽  
The One

Neusiedlersee (in German) / Fertö tó (in Hungarian) is a shallow lake at the Austro-Hungarian border. In the late 1970s, the question arose what to do in order to protect the lake against eutrophication. A preliminary report established the need for point-source control as well as gave first estimates for non-point source inputs. The proposed point-source control was quickly implemented, non-point sources were - among other topics - studied in detail in the period 1982 - 1986. The preliminary work had shown, based on integrated sampling and data from literature, that the aeolic input outweighed the one via water erosion (work was for totP only). In contrast to this, the 1982 - 1986 study showed that (a) water erosion by far dominates over aeolic inputs and (b) the size of nonpoint-source inputs was assessed for the largest catchment area in pronounced detail, whereas additional estimates were undertaken for smaller additional catchment areas. The methods as well as the results are presented in the following. The paper concludes with some remarks on the present management practice of nonpoint-source inputs.

scholarly journals Semi-analytical solutions of seismo-electromagnetic signals arising from the motional induction in 3-D multi-layered media: part II—numerical investigations

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Hengxin Ren ◽  
Ling Zeng ◽  
Yao-Chong Sun ◽  
Ken’ichi Yamazaki ◽  
Qinghua Huang ◽  
...  
Keyword(s):  
Point Source ◽  
Numerical Computation ◽  
Wave Velocity ◽  
Excellent Agreement ◽  
Seismic Waves ◽  
Averaging Method ◽  
Ground Surface ◽  
Induction Effect ◽  
Motional Induction ◽  
Electromagnetic Signals

AbstractIn this paper, numerical computations are carried out to investigate the seismo-electromagnetic signals arising from the motional induction effect due to an earthquake source embedded in 3-D multi-layered media. First, our numerical computation approach that combines discrete wavenumber method, peak-trough averaging method, and point source stacking method is introduced in detail. The peak-trough averaging method helps overcome the slow convergence problem, which occurs when the source–receiver depth difference is small, allowing us to consider any focus depth. The point source stacking method is used to deal with a finite fault. Later, an excellent agreement between our method and the curvilinear grid finite-difference method for the seismic wave solutions is found, which to a certain degree verifies the validity of our method. Thereafter, numerical computation results of an air–solid two-layer model show that both a receiver below and another one above the ground surface will record electromagnetic (EM) signals showing up at the same time as seismic waves, that is, the so-called coseismic EM signals. These results suggest that the in-air coseismic magnetic signals reported previously, which were recorded by induction coils hung on trees, can be explained by the motional induction effect or maybe other seismo-electromagnetic coupling mechanisms. Further investigations of wave-field snapshots and theoretical analysis suggest that the seismic-to-EM conversion caused by the motional induction effect will give birth to evanescent EM waves when seismic waves arrive at an interface with an incident angle greater than the critical angle θc = arcsin(Vsei/Vem), where Vsei and Vem are seismic wave velocity and EM wave velocity, respectively. The computed EM signals in air are found to have an excellent agreement with the theoretically predicted amplitude decay characteristic for a single frequency and single wavenumber. The evanescent EM waves originating from a subsurface interface of conductivity contrast will contribute to the coseismic EM signals. Thus, the conductivity at depth will affect the coseismic EM signals recorded nearby the ground surface. Finally, a fault rupture spreading to the ground surface, an unexamined case in previous numerical computations of seismo-electromagnetic signals, is considered. The computation results once again indicate the motional induction effect can contribute to the coseismic EM signals.

scholarly journals Multi-source SO<sub>2</sub> emissions retrievals and consistency of satellite and surface measurements with reported emissions

2017 ◽  
Author(s):  
Vitali Fioletov ◽  
Chris A. McLinden ◽  
Shailesh K. Kharol ◽  
Nickolay A. Krotkov ◽  
Can Li ◽  
...  
Keyword(s):  
Point Source ◽  
Single Point ◽  
Control Measures ◽  
Ozone Monitoring Instrument ◽  
So2 Emissions ◽  
Vertical Column ◽  
Wind Speeds ◽  
Surface Measurements ◽  
Best Fit

Abstract. Reported sulfur dioxide (SO2) emissions from U.S. and Canadian sources have declined dramatically since the 1990s as a result of emissions control measures. Observations from the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite and ground-based in-situ measurements are examined to verify whether the observed changes from SO2 abundance measurements are quantitatively consistent with the reported changes in emissions. To make this connection, a new method to link SO2 emissions and satellite SO2 measurements was developed. The method is based on fitting satellite SO2 vertical column densities (VCDs) to a set of functions of OMI pixel coordinates and wind speeds, where each function represents a statistical model of a plume from a single point source. The concept is first demonstrated using sources in North America, and then applied to Europe. The correlation coefficient between OMI-measured VCDs (with a local bias removed) and SO2 VCDs derived here using reported emissions for 1° by 1° gridded data is 0.91 and the best-fit line has a slope near unity, confirming a very good agreement between observed SO2 VCDs and reported emissions. Having demonstrated their consistency, seasonal and annual mean SO2 VCD distributions are calculated, based on reported point-source emissions for the period 1980–2015, as would have been seen by OMI. This consistency is further substantiated as the emissions-derived VCDs also show a high correlation with annual mean SO2 surface concentrations at 50 regional monitoring stations.

Water quality modeling in the watershed-based approach for waste load allocations

1998 ◽  
Vol 38 (10) ◽  
pp. 165-172 ◽  
Author(s):  
Ruochuan Gu ◽  
Mei Dong
Keyword(s):  
Water Quality ◽  
Point Source ◽  
Water Quality Modeling ◽  
Point Sources ◽  
Low Flow ◽  
Quality Analysis ◽  
Management Approach ◽  
Water Quality Control ◽  
Quality Modeling ◽  
Waste Load

The conventional method for waste load allocations (WLA) employs spatial-differentiation, considering individual point sources, and temporal-integration, using a constant flow, typically 7Q10 low flow. This paper presents a watershed-based seasonal management approach, in which non-point source as well as point sources are incorporated, seasonal design flows are used for water quality analysis, and WLA are performend in a watershed scale. The strategy for surface water quality modeling in the watershed-based approach is described. The concept of seasonal discharge management is discussed and suggested for the watershed-based approach. A case study using the method for the Des Moines River, Iowa, USA is conducted. Modeling considerations and procedure are presented. The significance of non-point source pollutant load and its impact on water quality of the river is evaluated by analyzing field data. A water quality model is selected and validated against field measurements. The model is applied to projections of future water quality situations under different watershed management and water quality control scenarios with respect to river flow and pollutant loading rate.

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