199 research outputs found
Model for triggering of non-volcanic tremor by earthquakes
There is evidence of tremor triggering by seismic waves emanating from
distant large earthquakes. The frequency content of both triggered and ambient
tremor are largely identical, suggesting that this property does not depend
directly on the nature of the source. We show here that the model of plate
dynamics developed earlier by us is an appropriate tool for describing tremor
triggering. In the framework of this model, tremor is an internal response of a
fault to a failure triggered by external disturbances. The model predicts
generation of radiation in a frequency range defined by the fault parameters.
Thus, although the amplitude and duration of a tremor burst may reflect the
"personality" of the source, the frequency content does not. The model also
explains why a tremor has no clear impulsive phase, in contrast to earthquakes.
The relationship between tremor and low frequency earthquakes is discussed.Comment: 9 pages, 1 figur
Model of deep non-volcanic tremor part I: ambient and triggered tremor
There is evidence of triggering of tremor by seismic waves emanating from
distant large earthquakes. The frequency contents of triggered and ambient
tremor are largely identical, suggesting that tremor does not depend directly
on the nature of the source. We show here that the model of plate dynamics
developed earlier by us is an appropriate tool for describing the onset of
tremor. In the framework of this model, tremor is an internal response of a
fault to a failure triggered by external disturbances. The model predicts
generation of radiation in a frequency range defined by the fault parameters.
Other specific features predicted are: the upper limit of the size of the
emitting area is a few dozen km; tremor accompanies earthquakes and aseismic
slip; the frequency content of tremor depends on the type of failure. The model
also explains why a tremor has no clear impulsive phase, in contrast to
earthquakes. A comparatively small effective normal stress (hence a high fluid
pressure) is required to make the model consistent with observed tremor
parameters. Our model indicates that tremor is not necessarily a superposition
of low frequency earthquakes, as commonly assumed, although the latter may
trigger them. The approach developed complements the conventional viewpoint
which assumes that tremor reflects a frictional process with low rupture speed.
Essentially our model adds the hypothesis that resonant-type oscillations exist
inside a fault. This addition may change our understanding of the nature of
tremor in general, and the methods of its identification and location in
particular.Comment: 32 pages, 16 figures. arXiv admin note: text overlap with
arXiv:1202.091
How does dissipation affect the transition from static to dynamic macroscopic friction?
Description of the transitional process from a static to a dynamic frictional
regime is a fundamental problem of modern physics. Previously we developed a
model based on the well-known Frenkel-Kontorova model to describe dry
macroscopic friction. Here this model has been modified to include the effect
of dissipation in derived relations between the kinematic and dynamic
parameters of a transition process. The main (somewhat counterintuitive) result
is a demonstration that the rupture (i.e. detachment front) velocity of the
slip pulse which arises during the transition does not depend on friction. The
only parameter (besides the elastic and plastic properties of the medium)
controlling the rupture velocity is the shear to normal stress ratio. In
contrast to the rupture velocity, the slip velocity does depend on friction.
The model we have developed describes these processes over a wide range of
rupture and slip velocities (up to 7 orders of magnitude) allowing, in
particular, the consideration of seismic events ranging from regular
earthquakes, with rupture velocities on the order of a few km/s, to slow slip
events, with rupture velocities of a few km/day.Comment: 21 pages, 12 figure
Transition from static to dynamic macroscopic friction in the framework of the Frenkel-Kontorova model
A new generation of experiments on dry macroscopic friction has revealed that
the transition from static to dynamic friction is essentially a spatially and
temporally non-uniform process, initiated by a rupture-like detachment front.
We show the suitability of the Frenkel-Kontorova model for describing this
transition. The model predicts the existence of two types of detachment fronts,
explaining both the variability and abrupt change of velocity observed in
experiments. The quantitative relation obtained between the velocity of the
detachment front and the ratio of shear to normal stress is consistent with
experiments. The model provides a functional dependence between slip velocity
and shear stress, and predicts that slip velocity is independent of normal
stress. Paradoxically, the transition from static to dynamic friction does not
depend explicitly on ether the static or the dynamic friction coefficient,
although the beginning and end of transition process are controlled by these
coefficients.Comment: 16 pages, 8 figure
Understanding the Impact of Open-Framework Conglomerates on Water-Oil Displacements: Victor Interval of the Ivishak Reservoir, Prudhoe Bay Field, Alaska
The Victor Unit of the Ivishak Formation in the Prudhoe Bay Oilfield is
characterized by high net-to-gross fluvial sandstones and conglomerates. The
highest permeability is found within sets of cross-strata of open-framework
conglomerate (OFC). They are preserved within unit bar deposits and assemblages
of unit bar deposits within compound (braid) bar deposits. They are thief zones
limiting enhanced oil recovery. We incorporate recent research that has
quantified important attributes of their sedimentary architecture within
preserved deposits. We use high-resolution models to demonstrate the
fundamental aspects of their control on oil production rate, water breakthrough
time, and spatial and temporal distribution of residual oil saturation. We
found that when the pressure gradient is oriented perpendicular to the
paleoflow direction, the total oil production and the water breakthrough time
are larger, and remaining oil saturation is smaller, than when it is oriented
parallel to paleoflow. The pressure difference between production and injection
wells does not affect sweep efficiency, although the spatial distribution of
oil remaining in the reservoir critically depends on this value. Oil sweep
efficiency decreases slightly with increase in the proportion of OFC
cross-strata. Whether or not clusters of connected OFC span the domain does not
visibly affect sweep efficiency.Comment: 27 pages including 14 figure
Computational technique for improvement of the position-weight matrices for the DNA/protein binding sites
Position-weight matrices (PWMs) are broadly used to locate transcription factor binding sites in DNA sequences. The majority of existing PWMs provide a low level of both sensitivity and specificity. We present a new computational algorithm, a modification of the Staden–Bucher approach, that improves the PWM. We applied the proposed technique on the PWM of the GC-box, binding site for Sp1. The comparison of old and new PWMs shows that the latter increase both sensitivity and specificity. The statistical parameters of GC-box distribution in promoter regions and in the human genome, as well as in each chromosome, are presented. The majority of commonly used PWMs are the 4-row mononucleotide matrices, although 16-row dinucleotide matrices are known to be more informative. The algorithm efficiently determines the 16-row matrices and preliminary results show that such matrices provide better results than 4-row matrices
The features of Drosophila core promoters revealed by statistical analysis
BACKGROUND: Experimental investigation of transcription is still a very labor- and time-consuming process. Only a few transcription initiation scenarios have been studied in detail. The mechanism of interaction between basal machinery and promoter, in particular core promoter elements, is not known for the majority of identified promoters. In this study, we reveal various transcription initiation mechanisms by statistical analysis of 3393 nonredundant Drosophila promoters. RESULTS: Using Drosophila-specific position-weight matrices, we identified promoters containing TATA box, Initiator, Downstream Promoter Element (DPE), and Motif Ten Element (MTE), as well as core elements discovered in Human (TFIIB Recognition Element (BRE) and Downstream Core Element (DCE)). Promoters utilizing known synergetic combinations of two core elements (TATA_Inr, Inr_MTE, Inr_DPE, and DPE_MTE) were identified. We also establish the existence of promoters with potentially novel synergetic combinations: TATA_DPE and TATA_MTE. Our analysis revealed several motifs with the features of promoter elements, including possible novel core promoter element(s). Comparison of Human and Drosophila showed consistent percentages of promoters with TATA, Inr, DPE, and synergetic combinations thereof, as well as most of the same functional and mutual positions of the core elements. No statistical evidence of MTE utilization in Human was found. Distinct nucleosome positioning in particular promoter classes was revealed. CONCLUSION: We present lists of promoters that potentially utilize the aforementioned elements/combinations. The number of these promoters is two orders of magnitude larger than the number of promoters in which transcription initiation was experimentally studied. The sequences are ready to be experimentally tested or used for further statistical analysis. The developed approach may be utilized for other species
Understanding the Impact of Open-Framework Conglomerates on Water-Oil Displacements: Victor Interval of the Ivishak Reservoir, Prudhoe Bay Field, Alaska
The Victor Unit of the Ivishak Formation in the Prudhoe Bay Oilfield is characterized by high net-to-gross fluvial sandstones and conglomerates. The highest permeability is found within sets of cross-strata of open-framework conglomerate (OFC). These cross-strata are preserved within unit-bar deposits and assemblages of unit-bar deposits within compound (braid)-bar deposits, and may form thief zones limiting enhanced oil recovery. We incorporate recent research that has quantified important attributes of preserved sedimentary architecture into high-resolution models. Waterflooding experiments using these models demonstrate the control that such architecture has on oil production rate, water breakthrough time, and spatial and temporal distribution of residual oil saturation. We found that when the pressure gradient is orientated perpendicular to the palaeoflow direction, the total oil production and the water breakthrough time are larger, and the remaining oil saturation is smaller, than when it is orientated parallel to palaeoflow. The pressure difference between production and injection wells does not affect sweep efficiency, although the spatial distribution of oil remaining in the reservoir critically depends on this value. Oil sweep efficiency decreases slightly with increase in the proportion of OFC cross-strata. Whether or not clusters of connected OFC span the domain does not visibly affect sweep efficiency
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