The effects of rheological layering on post-seismic deformation

We examine the effects of rheological layering on post-seismic deformation using models of an elastic layer over a viscoelastic layer and a viscoelastic half-space. We extend a general linear viscoelastic theory we have previously proposed to models with two layers over a half-space, although we only consider univiscous Maxwell and biviscous Burgers rheologies. In layered viscoelastic models, there are multiple mechanical timescales of post-seismic deformation; however, not all of these timescales arise as distinct phases of post-seismic relaxation observed at the surface. The surface displacements in layered models with only univiscous, Maxwell viscoelastic rheologies always exhibit one exponential-like phase of relaxation. Layered models containing biviscous rheologies may produce multiple phases of relaxation, where the distinctness of the phases depends on the geometry and the contrast in strengths between the layers. Post-seismic displacements in models with biviscous rheologies can often be described by logarithmic functions

Interseismic strain accumulation: Spin-up, cycle invariance, and irregular rupture sequences

Using models of infinite length strike-slip faults in an elastic layer above linear viscoelastic regions, we investigate interseismic deformation. In the models we investigate, interseismic strain accumulation on mature faults is the result of the cumulative effects of all previous ruptures and is independent of the fault loading conditions. The time for a fault to spin-up to a mature state depends on the rheologies and the fault loading conditions. After the model has spun-up, the temporal variation of shear stresses is determined by the fault slip rate and model rheologies. The change in stress during spin-up depends on the slip rate, rheologies, and fault loading conditions but is independent of the magnitude of the initial stress. Over enough cycles such that the cumulative deformation is block-like, the average mature interseismic velocities are equal to the interseismic velocities of an elastic model with the same geometry and distribution of shear moduli. In a model that has spun-up with the fault rupturing periodically, the cumulative deformation is block-like at the end of each seismic cycle, and the interseismic deformation is cycle-invariant (i.e., the same in all cycles). When the fault ruptures nonperiodically, the fault spins up to a mature state that is the same as if the fault had ruptured periodically with the mean slip rate. When the fault slip rate within each cycle varies, the interseismic deformation evolves toward the cycle-invariant deformation determined by the most recent fault slip rate. Around a fault whose slip rate has been faster (slower) than average, interseismic velocities are larger (smaller) than the cycle-invariant velocities and increase (decrease) from cycle to cycle

Estimated likelihood of observing a large earthquake on a continental low‐angle normal fault and implications for low‐angle normal fault activity

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106807/1/grl51557.pd

The weight of the mountains: Constraints on tectonic stress, friction, and fluid pressure in the 2008 Wenchuan earthquake from estimates of topographic loading

Though it is widely recognized that large mountain ranges produce significant stresses in the Earth's crust, these stresses are not commonly quantified. Nonetheless, near large mountains topography may affect fault activity by changing the stress balance on the faults. In this work, we calculate the stress field from topography in the Longmen Shan (Sichuan, China) and resolve those stresses on several models of the faults that ruptured in the 2008 Mw 7.9 Wenchuan earthquake. We find that the topography results in shear stresses up to 20 MPa and normal stresses up to 80 MPa on the faults, with significant variability across the faults. Topographic stresses generally load the fault in a normal and left‐lateral shear sense, opposite to the inferred coseismic slip sense, and thus inhibit the coseismic slip. We estimate the tectonic stress needed to overcome topographic and lithostatic stresses by assuming that the direction of maximum shear accumulated on the faults is roughly collinear with the inferred coseismic slip. We further estimate the static friction and pore fluid pressure assuming that the fault was, on average, at Mohr‐Coulomb failure at the time of the Wenchuan earthquake. We use a Bayesian inversion strategy, yielding posterior probability distributions for the estimated parameters. We find most likely estimates of maximum tectonic compressive stress near 0.6 ρgz and oriented ∼E‐W, and minimum tectonic stress near 0.2 ρgz. Static friction on the fault is near 0.2, and pore fluid pressure is between 0 and 0.4 of the total pressure.Key PointsTopographic stress is significant on Wenchuan faultsTopographic stresses resist tectonic slipTectonic stress, friction, and fluid pressure estimatedPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111754/1/jgrb51070.pd

Prevalence and Characteristics of Borderline Intellectual Functioning in a Cohort of Patients With Polysubstance Use Disorder

Objective: To determine the prevalence and associated demographic and clinical features of borderline intellectual functioning (BIF) among individuals with polysubstance use disorder (pSUD). Methods: We applied a cross-sectional analytical design to data from the Norwegian STAYER study (n = 162), a cohort study of patients with a pSUD from the Stavanger University hospital catchment area. We used Wechsler Abbreviated Scale of Intelligence Full Scale IQ (FSIQ) to define BIF (FSIQ = 70–85) and non-BIF (FSIQ = >85) and collected demographic and clinical data using semi-structured interviews and self-reports on the Symptom Checklist 90-Revised (SCL-90-R) and the Satisfaction With Life Scale (SWLS). Results: The prevalence of BIF was 18% in the present study. The presence of BIF was associated with higher SCL-90-R GSI scores than in the non-BIF group. There were no significant differences between the BIF and non-BIF groups regarding age, gender, participation in meaningful daily activity, years of work experience, years of education, satisfaction with life, level of care, treatment attempts, age at substance-use onset, years of substance use, history of injecting drugs, or age of onset of injecting drugs. Conclusion: The present study confirmed a higher prevalence of BIF among patients with pSUD than expected from the distribution of IQ scores in a general population. Elevated SCL-90-R GSI scores suggested that BIF is associated with increased psychological distress in patients receiving treatment for pSUD. Further studies on this association, and its effect on treatment procedure and outcomes are strongly warranted.publishedVersio

Measurement and calculation of levitation forces between magnets and granular superconductors

Recent developments indicate that exploitation of the phenomenon of magnetic levitation may become one of the most important near-term applications of high-T(sub c) superconductivity. Because of this, the interaction between a strong permanent magnet(PM) and bulk high-T(sub c) superconductor (HTSC) is currently a subject of much interest. We have studied central features of the mechanics of PM-HTSC systems of simple geometries. Here we report experimental results for the components of the levitation force, their associated stiffness and mechanical ac-loss. To analyze the observed behavior a theoretical framework based on critical-state considerations is developed. It will be shown that all the mechanical properties can be explained consistently at a quantitative level wing a minimum of model parameters

Central peak position in magnetization loops of high-TcT_c superconductors

Exact analytical results are obtained for the magnetization of a superconducting thin strip with a general behavior J_c(B) of the critical current density. We show that within the critical-state model the magnetization as function of applied field, B_a, has an extremum located exactly at B_a=0. This result is in excellent agreement with presented experimental data for a YBCO thin film. After introducing granularity by patterning the film, the central peak becomes shifted to positive fields on the descending field branch of the loop. Our results show that a positive peak position is a definite signature of granularity in superconductors.Comment: $ pages, 6 figure

Predicting risk for radiographic damage in rheumatoid arthritis:comparative analysis of the multi-biomarker disease activity score and conventional measures of disease activity in multiple studies

Pathophysiology and treatment of rheumatic disease