929 research outputs found
Andrade, Omori and Time-to-failure Laws from Thermal Noise in Material Rupture
Using the simplest possible ingredients of a rupture model with thermal
fluctuations, we provide an analytical theory of three ubiquitous empirical
observations obtained in creep (constant applied stress) experiments: the
initial Andrade-like and Omori-like decay of the rate of deformation and
of fiber ruptures and the critical time-to-failure behavior of
acoustic emissions just prior to the macroscopic rupture. The lifetime of the
material is controlled by a thermally activated Arrhenius nucleation process,
describing the cross-over between these two regimes. Our results give further
credit to the idea proposed by Ciliberto et al. that the tiny thermal
fluctuations may actually play an essential role in macroscopic deformation and
rupture processes at room temperature. We discover a new re-entrant effect of
the lifetime as a function of quenched disorder amplitude.Comment: 4 pages with 1 figur
Probing Human Response Times
In a recent preprint \cite{eck}, the temporal dynamics of an e-mail network
has been investigated by J.P. Eckmann, E. Moses and D. Sergi. Specifically, the
time period between an e-mail message and its reply were recorded. It will be
shown here that their data agrees quantitatively with the frame work proposed
to explain a recent experiment on the response of ``internauts'' to a news
publication \cite{www2} despite differences in communication channels, topics,
time-scale and socio-economic characteristics of the two population. This
suggest a generalized response time distribution for human
populations in the absence of deadlines with important implications for
psychological and social studies as well the study of dynamical networks.Comment: 6 pages including 2 figures. Subm. for Proceedings of Frontier
Science 200
Bath's law Derived from the Gutenberg-Richter law and from Aftershock Properties
The empirical Bath's law states that the average difference in magnitude
between a mainshock and its largest aftershock is 1.2, regardless of the
mainshock magnitude. Following Vere-Jones [1969] and Console et al. [2003], we
show that the origin of Bath's law is to be found in the selection procedure
used to define mainshocks and aftershocks rather than in any difference in the
mechanisms controlling the magnitude of the mainshock and of the aftershocks.
We use the ETAS model of seismicity, which provides a more realistic model of
aftershocks, based on (i) a universal Gutenberg-Richter (GR) law for all
earthquakes, and on (ii) the increase of the number of aftershocks with the
mainshock magnitude. Using numerical simulations of the ETAS model, we show
that this model is in good agreement with Bath's law in a certain range of the
model parameters.Comment: major revisions, in press in Geophys. Res. Let
Predictability in the ETAS Model of Interacting Triggered Seismicity
As part of an effort to develop a systematic methodology for earthquake
forecasting, we use a simple model of seismicity based on interacting events
which may trigger a cascade of earthquakes, known as the Epidemic-Type
Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare
(unrenormalized) Omori law, the Gutenberg-Richter law and the idea that large
events trigger more numerous aftershocks. For simplicity, we do not use the
information on the spatial location of earthquakes and work only in the time
domain. We offer an analytical approach to account for the yet unobserved
triggered seismicity adapted to the problem of forecasting future seismic rates
at varying horizons from the present. Tests presented on synthetic catalogs
validate strongly the importance of taking into account all the cascades of
still unobserved triggered events in order to predict correctly the future
level of seismicity beyond a few minutes. We find a strong predictability if
one accepts to predict only a small fraction of the large-magnitude targets.
However, the probability gains degrade fast when one attempts to predict a
larger fraction of the targets. This is because a significant fraction of
events remain uncorrelated from past seismicity. This delineates the
fundamental limits underlying forecasting skills, stemming from an intrinsic
stochastic component in these interacting triggered seismicity models.Comment: Latex file of 20 pages + 15 eps figures + 2 tables, in press in J.
Geophys. Re
Correlations and invariance of seismicity under renormalization-group transformations
The effect of transformations analogous to those of the real-space
renormalization group are analyzed for the temporal occurrence of earthquakes.
The distribution of recurrence times turns out to be invariant under such
transformations, for which the role of the correlations between the magnitudes
and the recurrence times are fundamental. A general form for the distribution
is derived imposing only the self-similarity of the process, which also yields
a scaling relation between the Gutenberg-Richter b-value, the exponent
characterizing the correlations, and the recurrence-time exponent. This
approach puts the study of the structure of seismicity in the context of
critical phenomena.Comment: Short paper. I'll be grateful to get some feedbac
Universal mean moment rate profiles of earthquake ruptures
Earthquake phenomenology exhibits a number of power law distributions
including the Gutenberg-Richter frequency-size statistics and the Omori law for
aftershock decay rates. In search for a basic model that renders correct
predictions on long spatio-temporal scales, we discuss results associated with
a heterogeneous fault with long range stress-transfer interactions. To better
understand earthquake dynamics we focus on faults with Gutenberg-Richter like
earthquake statistics and develop two universal scaling functions as a stronger
test of the theory against observations than mere scaling exponents that have
large error bars. Universal shape profiles contain crucial information on the
underlying dynamics in a variety of systems. As in magnetic systems, we find
that our analysis for earthquakes provides a good overall agreement between
theory and observations, but with a potential discrepancy in one particular
universal scaling function for moment-rates. The results reveal interesting
connections between the physics of vastly different systems with avalanche
noise.Comment: 13 pages, 5 figure
Power Law Distributions of Seismic Rates
We report an empirical determination of the probability density functions
of the number of earthquakes in finite space-time
windows for the California catalog. We find a stable power law tail
with exponent for all
space ( to km) and time intervals (0.1 to 1000
days). These observations, as well as the non-universal dependence on
space-time windows for all different space-time windows simultaneously, are
explained by solving one of the most used reference model in seismology (ETAS),
which assumes that each earthquake can trigger other earthquakes. The data
imposes that active seismic regions are Cauchy-like fractals, whose exponent
is well-constrained by the seismic rate data.Comment: 5 pages with 1 figur
Billboard Advertisement and Racial Perception in Ghana
This paper examines why business people in Ghana prefer using images of white people on their billboard outdoor advertisements. To attain the study’s objective, a cross-sectional survey was used. Data was collected from only a section of retail and wholesale businesses within the Ejisu and Juaben districts in the Ashanti Region of Ghana which use images of white people on their billboard outdoor advertisement. The survey findings show that retail and wholesale businesses use images of white people on their outdoor billboard advertisements because they are more attractive than images of black people. Also, the use of images of white people indicates a seal of professionalism, desirability, and quality services. The survey’s discovery reveals the racial perceptions of the white race in comparison with the black race by most African business people. The usage of the images of white people as the symbolic representation of ideal beauty, attractions, quality products and services, and model of authentic marketization has unfolded some of the factors that stymie the utilization of the images of the black people on an outdoor billboard advertisement. This paper contends that there is a necessity for a balanced moral reasoning and constructive racial perception of images of black people and self-identification
Violation of the scaling relation and non-Markovian nature of earthquake aftershocks
The statistical properties of earthquake aftershocks are studied. The scaling
relation for the exponents of the Omori law and the power-law calm time
distribution (i.e., the interoccurrence time distribution), which is valid if a
sequence of aftershocks is a singular Markovian process, is carefully examined.
Data analysis shows significant violation of the scaling relation, implying the
non-Markovian nature of aftershocks.Comment: 11 pages, 2 figures, 1 table. Dedicated to Francois Bardou
(1968-2006
Acoustic Emission Monitoring of the Syracuse Athena Temple: Scale Invariance in the Timing of Ruptures
We perform a comparative statistical analysis between the acoustic-emission time series from the ancient Greek Athena temple in Syracuse and the sequence of nearby earthquakes. We find an apparent association between acoustic-emission bursts and the earthquake occurrence. The waiting-time distributions for acoustic-emission and earthquake time series are described by a unique scaling law indicating self-similarity over a wide range of magnitude scales. This evidence suggests a correlation between the aging process of the temple and the local seismic activit
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