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

Comparison of the planktonic diatom community and net diatom community of Neureclipsis crepuscularis.

The caddisfly Neureclipsis crepuscularis (Polycentropodidae) filters the water column downstream of lake effluents. Although they are predaceous, algal communities commonly thrive on their nets. I analyzed the diatom communities in these nets on two branches of a river in northern Michigan, USA. The net community was compared to the local plankton community, and at least one taxon per site was significantly different (n=2, p<0.05), and the abundance of many other taxa was noticeably different. Shannon-Weiner species diversity indices supported the observed differences in taxa, and also gave an overall analysis of difference between the two study sites. The results do show a difference in diatom community composition, but we can only speculate about the mechanism of the difference. Behavioral considerations (i.e., gardening) are a possibility, but the difference can also be explained in terms of diatom morphology, net mesh size, and the ecology of the specific diatom flora. A lack of statistical power limited the thoroughness of the study, as most of the data indicated that more differences in taxa could exist. Neureclipsis crepuscularis nets have the potential to be important in lotic diatom community assessments and as bioindicators, and this unique phenomenon deserves further study.http://deepblue.lib.umich.edu/bitstream/2027.42/54977/1/3418.pd

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

Benthic invertebrate food selectivity in northern Lake Michigan following the invasion of dreissenid mussels (Dreissena polymorpha and D. bugensis)

Senior Honor's ThesisThis study focused on the interaction between the new benthic algal community and invertebrate grazers. The objective of this study was to examine whether grazers are exploiting the new benthic algal food source. Specifically, I hypothesize that invertebrates have shifted their dietary habits to accommodate this dreissenid-mediated benthic algal resource. 3http://deepblue.lib.umich.edu/bitstream/2027.42/61357/1/Bambakidis_Ted_2005.pd

Fresh Frozen Plasma Resuscitation Provides Neuroprotection Compared to Normal Saline in a Large Animal Model of Traumatic Brain Injury and Polytrauma

We have previously shown that early treatment with fresh frozen plasma (FFP) is neuroprotective in a swine model of hemorrhagic shock (HS) and traumatic brain injury (TBI). However, it remains unknown whether this strategy would be beneficial in a more clinical polytrauma model. Yorkshire swine (42?50?kg) were instrumented to measure hemodynamic parameters, brain oxygenation, and intracranial pressure (ICP) and subjected to computer-controlled TBI and multi-system trauma (rib fracture, soft-tissue damage, and liver injury) as well as combined free and controlled hemorrhage (40% blood volume). After 2?h of shock (mean arterial pressure, 30?35?mm Hg), animals were resuscitated with normal saline (NS; 3?volume) or FFP (1?volume; n=6/group). Six hours postresuscitation, brains were harvested and lesion size and swelling were evaluated. Levels of endothelial-derived vasodilator endothelial nitric oxide synthase (eNOS) and vasoconstrictor endothelin-1 (ET-1) were also measured. FFP resuscitation was associated with reduced brain lesion size (1005.8 vs. 2081.9?mm3; p=0.01) as well as swelling (11.5% vs. 19.4%; p=0.02). Further, FFP-resuscitated animals had higher brain oxygenation as well as cerebral perfusion pressures. Levels of cerebral eNOS were higher in the FFP-treated group (852.9 vs. 816.4?ng/mL; p=0.03), but no differences in brain levels of ET-1 were observed. Early administration of FFP is neuroprotective in a complex, large animal model of polytrauma, hemorrhage, and TBI. This is associated with a favorable brain oxygenation and cerebral perfusion pressure profile as well as higher levels of endothelial-derived vasodilator eNOS, compared to normal saline resuscitation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140168/1/neu.2014.3535.pd