245 research outputs found
Persistence and Quiescence of Seismicity on Fault Systems
We study the statistics of simulated earthquakes in a quasistatic model of
two parallel heterogeneous faults within a slowly driven elastic tectonic
plate. The probability that one fault remains dormant while the other is active
for a time Dt following the previous activity shift is proportional to the
inverse of Dt to the power 1+x, a result that is robust in the presence of
annealed noise and strength weakening. A mean field theory accounts for the
observed dependence of the persistence exponent x as a function of
heterogeneity and distance between faults. These results continue to hold if
the number of competing faults is increased. This is related to the persistence
phenomenon discovered in a large variety of systems, which specifies how long a
relaxing dynamical system remains in a neighborhood of its initial
configuration. Our persistence exponent is found to vary as a function of
heterogeneity and distance between faults, thus defining a novel universality
class.Comment: 4 pages, 3 figures, Revte
Localized Amplification of Seismic Waves and Correlation with Damage Due to the Northridge Earthquake: Evidence for Focusing in Santa Monica
The analysis of seismograms from 32 aftershocks recorded by 98 seismic stations installed after the Northridge earthquake in the San Fernando Valley, the Santa Monica Mountains, and Santa Monica, California, indicates that the enhanced damage in Santa Monica is explained in the main by focusing due to a lens structure at a depth of several kilometers beneath the surface and having a finite lateral extent. The diagnosis was made from the observation of late-arriving S phases with large amplitudes, localized in the zones of large damage. The azimuths and angles of incidence of the seismic rays that give rise to the greatest focusing effects correspond to radiation that would have emerged from the lower part of the rupture surface of the mainshock. Thus the focusing and, hence, the large damage in Santa Monica were highly dependent on the location of the Northridge event, and an earthquake of similar size, located as little as one source dimension away, would not be likely to repeat this pattern. We show from coda wave analysis that the influence of surface geology as well as site effects on damage in Santa Monica is significantly smaller than are the focusing effects
Seasonally Forced SIR Systems Applied to Respiratory Infectious Diseases, Bifurcations, and Chaos
We investigate models to describe respiratory diseases with fast mutating virus pathogens such that after some years the aquired resistance is lost and hosts can be infected with new variants of the pathogen. Such models were initially suggested for respiartory diseases like influenza, showing complex dynamics in reasonable parameter regions when comparing to historic empirical influenza like illness data, e.g., from Ille de France. The seasonal forcing typical for respiratory diseases gives rise to the different rich dynamical scenarios with even small parameter changes. Especially the seasonality of the infection leads for small values already to period doubling bifurcations into chaos, besides additional coexisting attractors. Such models could in the future also play a role in understanding the presently experienced COVID-19 pandemic, under emerging new variants and with only limited vaccine efficacies against newly upcoming variants. From first period doubling bifurcations, we can eventually infer at which close by parameter regions complex dynamics including deterministic chaos can arise.Marie SkĆodowska-Curie grant agreement No. 79249
Precession of a Freely Rotating Rigid Body. Inelastic Relaxation in the Vicinity of Poles
When a solid body is freely rotating at an angular velocity ,
the ellipsoid of constant angular momentum, in the space , has poles corresponding to spinning about the minimal-inertia and
maximal-inertia axes. The first pole may be considered stable if we neglect the
inner dissipation, but becomes unstable if the dissipation is taken into
account. This happens because the bodies dissipate energy when they rotate
about any axis different from principal. In the case of an oblate symmetrical
body, the angular velocity describes a circular cone about the vector of
(conserved) angular momentum. In the course of relaxation, the angle of this
cone decreases, so that both the angular velocity and the maximal-inertia axis
of the body align along the angular momentum. The generic case of an asymmetric
body is far more involved. Even the symmetrical prolate body exhibits a
sophisticated behaviour, because an infinitesimally small deviation of the
body's shape from a rotational symmetry (i.e., a small difference between the
largest and second largest moments of inertia) yields libration: the precession
trajectory is not a circle but an ellipse. In this article we show that often
the most effective internal dissipation takes place at twice the frequency of
the body's precession. Applications to precessing asteroids, cosmic-dust
alignment, and rotating satellites are discussed.Comment: 47 pages, 1 figur
Avalanches in the Weakly Driven Frenkel-Kontorova Model
A damped chain of particles with harmonic nearest-neighbor interactions in a
spatially periodic, piecewise harmonic potential (Frenkel-Kontorova model) is
studied numerically. One end of the chain is pulled slowly which acts as a weak
driving mechanism. The numerical study was performed in the limit of infinitely
weak driving. The model exhibits avalanches starting at the pulled end of the
chain. The dynamics of the avalanches and their size and strength distributions
are studied in detail. The behavior depends on the value of the damping
constant. For moderate values a erratic sequence of avalanches of all sizes
occurs. The avalanche distributions are power-laws which is a key feature of
self-organized criticality (SOC). It will be shown that the system selects a
state where perturbations are just able to propagate through the whole system.
For strong damping a regular behavior occurs where a sequence of states
reappears periodically but shifted by an integer multiple of the period of the
external potential. There is a broad transition regime between regular and
irregular behavior, which is characterized by multistability between regular
and irregular behavior. The avalanches are build up by sound waves and shock
waves. Shock waves can turn their direction of propagation, or they can split
into two pulses propagating in opposite directions leading to transient
spatio-temporal chaos. PACS numbers: 05.70.Ln,05.50.+q,46.10.+zComment: 33 pages (RevTex), 15 Figures (available on request), appears in
Phys. Rev.
Aperiodicity in one-way Markov cycles and repeat times of large earthquakes in faults
A common use of Markov Chains is the simulation of the seismic cycle in a
fault, i.e. as a renewal model for the repetition of its characteristic
earthquakes. This representation is consistent with Reid's elastic rebound
theory. Here it is proved that in {\it any} one-way Markov cycle, the
aperiodicity of the corresponding distribution of cycle lengths is always lower
than one. This fact concurs with observations of large earthquakes in faults
all over the world
Use of specific Green's functions for solving direct problems involving a heterogeneous rigid frame porous medium slab solicited by acoustic waves
A domain integral method employing a specific Green's function (i.e.,
incorporating some features of the global problem of wave propagation in an
inhomogeneous medium) is developed for solving direct and inverse scattering
problems relative to slab-like macroscopically inhomogeneous porous obstacles.
It is shown how to numerically solve such problems, involving both
spatially-varying density and compressibility, by means of an iterative scheme
initialized with a Born approximation. A numerical solution is obtained for a
canonical problem involving a two-layer slab.Comment: submitted to Math.Meth.Appl.Sc
On the Occurrence of Finite-Time-Singularities in Epidemic Models of Rupture, Earthquakes and Starquakes
We present a new kind of critical stochastic finite-time-singularity, relying
on the interplay between long-memory and extreme fluctuations. We illustrate it
on the well-established epidemic-type aftershock (ETAS) model for aftershocks,
based solely on the most solidly documented stylized facts of seismicity
(clustering in space and in time and power law Gutenberg-Richter distribution
of earthquake energies). This theory accounts for the main observations (power
law acceleration and discrete scale invariant structure) of critical rupture of
heterogeneous materials, of the largest sequence of starquakes ever attributed
to a neutron star as well as of earthquake sequences.Comment: Revtex document of 4 pages including 1 eps figur
The Slab Puzzle of the AlpineâMediterranean Region: Insights from a new, HighâResolution, ShearâWave Velocity Model of the Upper Mantle
Mediterranean tectonics since the Lower Cretaceous has been characterized by a multiâphase subduction and collision history with temporally and spatiallyâvariable, smallâscale plate configurations. A new shearâwave velocity model of the Mediterranean upper mantle (MeRE2020), constrained by a very large set of over 200,000 broadband (8â350 s), interâstation, Rayleighâwave, phaseâvelocity curves, illuminates the complex structure and fragmentation of the subducting slabs. Phaseâvelocity maps computed using these measurements were inverted for depthâdependent, shearâwave velocities using a stochastic particleâswarmâoptimization algorithm (PSO). The resulting threeâdimensional (3âD) model makes possible an inventory of slab segments across the Mediterranean. Fourteen slab segments of 200â800 km length alongâstrike are identified. We distinguish three categories of subducted slabs: attached slabs reaching down to the bottom of the model; shallow slabs of shorter length in downâdip direction, terminating shallower than 300 km depth; and detached slab segments. The location of slab segments are consistent with and validated by the intermediateâdepth seismicity, where it is present. The new highâresolution tomography demonstrates the intricate relationships between slab fragmentation and the evolution of the relatively small and highly curved subduction zones and collisional orogens characteristic of the Mediterranean realm
A feasibility test of CMT inversion using regional network of broad-band strong-motion seismographs for near-distance large earthquakes
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