Amplitude and phase fluctuations of seismic waves and characterization of small-scale heterogeneities in the earth.

2009 ◽  
Vol 126 (4) ◽  
pp. 2171
Author(s):  
Ru-Shan Wu ◽  
Xiao-Bi Xie ◽  
Yingcai Zheng
Keyword(s):  
Seismic Waves ◽  
Small Scale ◽  
Phase Fluctuations ◽  
The Earth

2-D random media with ellipsoidal autocorrelation functions

Geophysics ◽  
1993 ◽  
Vol 58 (9) ◽  
pp. 1359-1372 ◽  
Author(s):  
L. T. Ikelle ◽  
S. K. Yung ◽  
F. Daube
Keyword(s):  
Aspect Ratio ◽  
Seismic Data ◽  
Random Media ◽  
Large Scale ◽  
Seismic Waves ◽  
Homogeneous Medium ◽  
Small Scale ◽  
Arrival Times ◽  
The Earth ◽  
Pulse Arrival

The integration of surface seismic data with borehole seismic data and well‐log data requires a model of the earth which can explain all these measurements. We have chosen a model that consists of large and small scale inhomogeneities: the large scale inhomogeneities are the mean characteristics of the earth while the small scale inhomogeneities are fluctuations from these mean values. In this paper, we consider a two‐dimensional (2-D) model where the large scale inhomogeneities are represented by a homogeneous medium and small scale inhomogeneities are randomly distributed inside the homogeneous medium. The random distribution is characterized by an ellipsoidal autocorrelation function in the medium properties. The ellipsoidal autocorrelation function allows the parameterization of small scale inhomogeneities by two independent autocorrelation lengths a and b in the horizontal and the vertical Cartesian directions, respectively. Thus we can describe media in which the inhomogeneities are isotropic (a = b), or elongated in a direction parallel to either of the two Cartesian directions (a > b, a < b), or even taken to infinite extent in either dimension (e.g., a = infinity, b = finite: a 1-D medium) by the appropriate choice of the autocorrelation lengths. We also examine the response of seismic waves to this form of inhomogeneity. To do this in an accurate way, we used the finite‐difference technique to simulate seismic waves. Special care is taken to minimize errors due to grid dispersion and grid anisotropy. The source‐receiver configuration consists of receivers distributed along a quarter of a circle centered at the source point, so that the angle between the source‐receiver direction and the vertical Cartesian direction varies from 0 to 90 degrees. Pulse broadening, coda, and anisotropy (transverse isotropy) due to small scale inhomogeneities are clearly apparent in the synthetic seismograms. These properties can be recast as functions of the aspect ratio [Formula: see text] of the medium, especially the anisotropy and coda. For media with zero aspect ratio (1-D media), the coda energy is dominant at large angles. The coda energy gradually becomes uniformly distributed with respect to angle as the aspect ratio increases to unity. Our numerical results also suggest that, for small values of aspect ratio, the anisotropic behavior (i.e., the variations of pulse arrival times with angle) of the 2-D random media is similar to that of a 1-D random medium. The arrival times agree with the effective medium theory. As the aspect ratio increases to unity, the variations of pulse arrival times with angle gradually become isotropic. To retain the anisotropic behavior beyond the geometrical critical angle, we have used a low‐frequency pulse with a nonzero dc component.

The Qaanaaq airburst as an analog of seismic source in extraterrestrial atmospheres: seismic and infrasound investigation

2020 ◽  
Author(s):  
Foivos Karakostas ◽  
Nicholas Schmerr ◽  
Samuel Hop Bailey ◽  
Daniella Dellagiustina ◽  
Namrah Habib ◽  
...  
Keyword(s):  
Shock Wave ◽  
Wave Propagation ◽  
Solar System ◽  
Seismic Waves ◽  
Seismic Source ◽  
Shock Wave Propagation ◽  
Tectonic Activity ◽  
Seismic Sources ◽  
The Earth

&lt;p&gt;On July 25, 2018, a meteoroid-associated airburst occurred near the Qaanaaq town, in Greenland, at approximately 22:00 UTC (20:00 local time). The event generated seismic waves that were recorded by two stations of the Danish Seismological Network (TULEG and NEEM) and the bolide trajectory was consequently calculated by the NASA Center for Near-Earth Object Studies (CNEOS). The total impact energy, calculated by CNEOS was 2.1 kT of TNT and the brightest point on its trajectory corresponds to an altitude of around 43 km, at a distance of about 50 km S of the Qaanaaq town and 50 km N of the TULEG station and the Thule Air Force Base [1].&lt;/p&gt; &lt;p&gt;An airburst occurring over the icy surface of Greenland is a rare terrestrial analog for regions of the Solar System, where both an atmosphere and an icy surface exist. In the past, a variety of works had indicated the presence of ice on Titan, the biggest moon of Saturn (e.g. [2] and more recently [3]) and more precisely, the icy composition of mountains which are formed by tectonic activity [4]. Titan has a relatively thick atmosphere, compared to those of other moons in the Solar System, composed mainly (94%) of nitrogen [5]. The characterization of atmospheric meteoroid-associated seismic sources for Titan has a particular interest, as it is found that, contrary to other moons of the solar system, the presence of craters on its surface is extremely low (only about 0.4% according to [3]). The reason for this low cratering of the surface is the presence of the thick atmosphere, into which many of the meteoroids are entirely ablated into dust. Therefore, a methodology for the characterization of airbursts as seismic sources and the modeling of the associated generated seismic waves is necessary for a future seismic experiment, as any recorded signal will either be a direct atmospheric wave (nonlinear shock wave, or linear acoustic wave) or a seismic wave generated through the coupling of the atmospheric and solid/ice part.&lt;br /&gt;&amp;#160;&lt;br /&gt;In the present study, our aim is to perform a seismic investigation of the Greenland ice shell with the use of the airburst-associated seismic source. The performed tasks into which this effort has been divided, include the application of a technique which approaches the bolide as an atmospheric seismic source, the calculation of the distance of shock wave propagation in the atmosphere, the description of the mechanism of generation of the seismic waves in the atmosphere and the solid-icy part.&lt;/p&gt; &lt;p&gt;When the bolides enter the atmosphere of the Earth or that of any other body, shock waves are generated along the trajectory of the meteoroid. These waves are characterized by the overpressure that they generate, which create a clear pressure discontinuity in the atmosphere, referred to as the nonlinear part of the shock wave propagation. The propagation distance of this nonlinear wave is associated to the ratio of the meteoroid speed to the ambient sound speed, also known as the Mach number, as well as the physical diameter of the meteoroid. In this work, we compute this distance for the Earth case and for the known trajectory of the detected and examined bolide [1][6].&lt;/p&gt; &lt;p&gt;The methodology developed in this study can serve the seismic investigation of structures covered by ice on planets or planetary bodies with a relatively thick atmosphere, where airbursts can occur due to the friction of the meteoroid with the ambient atmospheric material. An ideal example of this case are the icy mountains of Titan, which are known to be formed by tectonic activity on the Saturn&amp;#8217;s moon [4]. The future Dragonfly mission to Titan will carry a seismometer as part of the DraGMet (Dragonfly Geophysics and Meteorology Package) payload [7]. Even if the primary goal of the mission is the characterization of the regolith properties, an eventual airburst and collection of seismic data near these mountainous icy structures, will be a great opportunity to investigate, through the identification of the associated waves and thus the investigation of the coupled seismic waves, the properties of this icy cover, its depth and composition.&lt;/p&gt; &lt;p&gt;References: [1] https://cneos.jpl.nasa.gov/fireballs/ [2] Sohl, F. et al. (1995) Icarus, 115, 278&amp;#8211;294 [3] Lopes R.M.C. et al. (2019) Nat Astron, [4] Radebaugh J. et al. (2007) Icarus, 192, 77-91, [5] Niemann H.B. et al. (2005) Nature, 438, 779&amp;#8211;784 [6] Schmerr, N. et al. (2018) Abstract P21E-3406, AGU Fall Meeting 2018, Washington DC [7] Lorenz R. et al. (2018) Johns Hop- kins APL Technical Digest, 34, 3&lt;/p&gt;

Optical and Chemical Characterization of Aerosols Emitted from Coal, Heavy and Light Fuel Oil, and Small-Scale Wood Combustion

2013 ◽  
Vol 48 (1) ◽  
pp. 827-836 ◽  
Author(s):  
Anna K. Frey ◽  
Karri Saarnio ◽  
Heikki Lamberg ◽  
Fanni Mylläri ◽  
Panu Karjalainen ◽  
...  
Keyword(s):  
Chemical Characterization ◽  
Fuel Oil ◽  
Small Scale ◽  
Wood Combustion

The habitable zone of Earth-mass planets around 47 UMa: results for land and water worlds

2003 ◽  
Vol 2 (1) ◽  
pp. 35-39 ◽  
Author(s):  
S. Franck ◽  
M. Cuntz ◽  
W. von Bloh ◽  
C. Bounama
Keyword(s):  
Surface Water ◽  
System Approach ◽  
Distinct Type ◽  
Integrated System ◽  
Habitable Zone ◽  
Stable Orbit ◽  
The Earth ◽  
Earth Like Planets ◽  
Very High

In a previous paper, we showed that Earth-type habitable planets around 47 UMa are in principle possible if a distinct set of conditions is warranted. These conditions include that the Earth-type planets have successfully formed and are orbitally stable and, in addition, that the 47 UMa star–planet system is relatively young ([lsim ]6 Gyr). We now extend this study by considering Earth-like planets with different land/ocean coverages. This study is again based on the so-called integrated system approach, which describes the photosynthetic biomass production taking into account a variety of climatological, biogeochemical and geodynamical processes. This approach implies a special characterization of the habitable zone defined for a distinct type of planet. We show that the likelihood of finding a habitable Earth-like planet on a stable orbit around 47 UMa critically depends on the percentage of the planetary land/ocean coverage. The likelihood is significantly increased for planets with a very high percentage of ocean surface (‘water worlds’).

scholarly journals Characterization of small-scale fisheries in the Camamu-Almada basin, southeast state of Bahia, Brazil

2008 ◽  
Vol 68 (4) ◽  
pp. 711-719 ◽  
Author(s):  
TCM. Souza ◽  
M. Petrere-Jr
Keyword(s):  
Low Income ◽  
Small Scale ◽  
Income Generation ◽  
Target Species ◽  
Market Prices ◽  
Marine Fishery ◽  
Small Scale Fisheries ◽  
Main Factor ◽  
Stock Abundance

In the Camamu-Almada basin, marine fishery is exclusively small-scale, with several structural deficiencies such as boats with low or absent navigational technology, lack of credit and low income. Local fishers complain that shrimp and lobster trawling fishing is the main factor responsible for low stock abundance, but they still persist in these activities as these two species command the highest market prices. So they feel that the target species are already over-fished. We suggest that proper management action, alternative ways of income generation and the payment of job insurance would help to mitigate the problem.

scholarly journals Molecular characterization of Listeria monocytogenes isolates from a small-scale meat processor in Montenegro, 2011–2014

2019 ◽  
Vol 79 ◽  
pp. 116-122 ◽  
Author(s):  
Ivana Zuber ◽  
Brankica Lakicevic ◽  
Ariane Pietzka ◽  
Dubravka Milanov ◽  
Vesna Djordjevic ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Molecular Characterization ◽  
Small Scale

Experimental Parameters Used to Study Pesticide Degradation in Soil

1996 ◽  
Vol 10 (1) ◽  
pp. 169-173 ◽  
Author(s):  
Michael R. Blumhorst
Keyword(s):  
Small Scale ◽  
Test Substance ◽  
Pesticide Degradation ◽  
Soil System ◽  
Experimental Parameters ◽  
Effective Cost ◽  
Cost Efficient ◽  
Efficient Mechanisms ◽  
Degradation In Soil

Characterization of pesticide degradation in soil is an important component in determining the environmental impact of agriculturally-applied pesticides. Several techniques currently are being used to generate these data, but small-scale laboratory studies remain one of the most effective, cost-efficient mechanisms of evaluating pesticide behavior in soil. With small-scale studies, many different environmental factors can be incorporated into the experimental design, and with the use of14C-labeled material, these studies (often referred to as soil degradation or soil metabolism studies) provide information on test substance persistence, degradation, volatilization, and mineralization. Care must be exercised, however, in selecting the experimental parameters to be used because of the potential adverse or artificial effects on the soil system.

Tribological Characterization of Machining at Very Small Contact Areas

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Michael R. Lovell ◽  
P. Cohen ◽  
Pradeep L. Menezes ◽  
R. Shankar
Keyword(s):  
High Speed ◽  
Friction Mechanisms ◽  
High Speed Steel ◽  
Small Scale ◽  
Machining Processes ◽  
Macroscopic Theory ◽  
Contact Areas ◽  
Tribological Characterization ◽  
Physical Phenomena

When machining miniaturized components, the contact conditions between the tool and the workpiece exhibit very small contact areas that are on the order of 10−5 mm2. Under these conditions, extremely high contact stresses are generated, and it is not clear whether macroscopic theories for the chip formation, cutting forces, and friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in very small scale machining processes so that evaluations of standard macroscale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using high-speed steel tools over a range of speeds, feeds, depths of cut, and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor τk were obtained. Based on the experimental results, it was determined that the standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in very small scale machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining processes were ascertained and discussed.

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