2,714 research outputs found
Geoid Anomalies and the Near-Surface Dipole Distribution of Mass
Although geoid or surface gravity anomalies cannot be uniquely related to an interior distribution of mass, they can be related to a surface mass distribution. However, over horizontal distances greater than about 100 km, the condition of isostatic equilibrium above the asthenosphere is a good approximation and the total mass per unit column is zero. Thus the surface distribution of mass is also zero. For this case we show that the surface gravitational potential anomaly can be uniquely related to a surface dipole distribution of mass. Variations in the thickness of the crust and lithosphere can be expected to produce undulations in the geoid
Élaboration et validation d’une échelle des agents de stress dans les organisations
Cette recherche a pour but d'expliciter les mécanismes du stress et d'établir puis valider une échelle hiérarchique des différents agents de stress dans les organisations.The object of this research is to elaborate a model of organizational stress and to establish a hierarchical scale of various organizational stressors in addition to validating such a scale.Many researchers, amongst them Beehr, Walsh and Taber have established, the fact that stress related to task role such as role ambiguity and non participation has an effect on fatigue, tension and job dissatisfaction. However, up to now, no effort has been made to take stock of the many different organizational stressors. Therefore, an organizational stressors scale was built using the Delphi Technique. The scale was then tested amongst 148 managers in 10 different organizations.This research demonstrated that there exists a relationship between organizational stress and psychological stress manifestation such as aggressiveness, depression and concentration problems, as well as physiological stress manifestation such as insomnia, gastrointestinal and respiratory problems. This research has also proved that there is a relationship between high organizational stress scores and a high rate of use or abuse of pharmaceutical products such as stimulants
A renormalization group model for the stick-slip behavior of faults
A fault which is treated as an array of asperities with a prescribed statistical distribution of strengths is described. For a linear array the stress is transferred to a single adjacent asperity and for a two dimensional array to three ajacent asperities. It is shown that the solutions bifurcate at a critical applied stress. At stresses less than the critical stress virtually no asperities fail on a large scale and the fault is locked. At the critical stress the solution bifurcates and asperity failure cascades away from the nucleus of failure. It is found that the stick slip behavior of most faults can be attributed to the distribution of asperities on the fault. The observation of stick slip behavior on faults rather than stable sliding, why the observed level of seismicity on a locked fault is very small, and why the stress on a fault is less than that predicted by a standard value of the coefficient of friction are outlined
Space-Time Clustering and Correlations of Major Earthquakes
Earthquake occurrence in nature is thought to result from correlated elastic
stresses, leading to clustering in space and time. We show that occurrence of
major earthquakes in California correlates with time intervals when
fluctuations in small earthquakes are suppressed relative to the long term
average. We estimate a probability of less than 1% that this coincidence is due
to random clustering.Comment: 5 pages, 3 figures. Submitted to PR
Earthquake forecasting and its verification
No proven method is currently available for the reliable short time
prediction of earthquakes (minutes to months). However, it is possible to make
probabilistic hazard assessments for earthquake risk. These are primarily based
on the association of small earthquakes with future large earthquakes. In this
paper we discuss a new approach to earthquake forecasting. This approach is
based on a pattern informatics (PI) method which quantifies temporal variations
in seismicity. The output is a map of areas in a seismogenic region
(``hotspots'') where earthquakes are forecast to occur in a future 10-year time
span. This approach has been successfully applied to California, to Japan, and
on a worldwide basis. These forecasts are binary--an earthquake is forecast
either to occur or to not occur. The standard approach to the evaluation of a
binary forecast is the use of the relative operating characteristic (ROC)
diagram, which is a more restrictive test and less subject to bias than maximum
likelihood tests. To test our PI method, we made two types of retrospective
forecasts for California. The first is the PI method and the second is a
relative intensity (RI) forecast based on the hypothesis that future
earthquakes will occur where earthquakes have occurred in the recent past.
While both retrospective forecasts are for the ten year period 1 January 2000
to 31 December 2009, we performed an interim analysis 5 years into the
forecast. The PI method out performs the RI method under most circumstances.Comment: 10(+1) pages, 5 figures, 2 tables. Submitted to Nonlinearl Processes
in Geophysics on 5 August 200
Network of recurrent events for the Olami-Feder-Christensen model
We numerically study the dynamics of a discrete spring-block model introduced
by Olami, Feder and Christensen (OFC) to mimic earthquakes and investigate to
which extent this simple model is able to reproduce the observed spatiotemporal
clustering of seismicty. Following a recently proposed method to characterize
such clustering by networks of recurrent events [Geophys. Res. Lett. {\bf 33},
L1304, 2006], we find that for synthetic catalogs generated by the OFC model
these networks have many non-trivial statistical properties. This includes
characteristic degree distributions -- very similar to what has been observed
for real seismicity. There are, however, also significant differences between
the OFC model and earthquake catalogs indicating that this simple model is
insufficient to account for certain aspects of the spatiotemporal clustering of
seismicity.Comment: 11 pages, 16 figure
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