Lubricated wrinkles: imposed constraints affect the dynamics of wrinkle coarsening

We study the dynamic coarsening of wrinkles in an elastic sheet that is compressed while lying on a thin layer of viscous liquid. When the ends of the sheet are instantaneously brought together by a small distance, viscous resistance initially prevents the sheet from adopting a globally buckled shape. Instead, the sheet accommodates the compression by wrinkling. Previous scaling arguments suggested that a balance between the sheet's bending stiffness and viscous effects lead to a wrinkle wavelength $\lambda$ that increases with time $t$ according to $\lambda\propto t^{1/6}$. We show that taking proper account of the compression constraint leads to a logarithmic correction of this result, $\lambda\propto (t/\log t)^{1/6}$. This correction is significant over experimentally observable time spans, and leads us to reassess previously published experimental data.Comment: 12 pages. Version accepted in Phys. Rev. Fluids (with small correction to bibliography

Modeling the shortening history of a fault tip fold using structural and geomorphic records of deformation

We present a methodology to derive the growth history of a fault tip fold above a basal detachment. Our approach is based on modeling the stratigraphic and geomorphic records of deformation, as well as the finite structure of the fold constrained from seismic profiles. We parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments. Assuming a stationary spatial pattern of deformation, we simulate the gradual warping and uplift of stratigraphic and geomorphic markers, which provides an estimate of the cumulative amounts of shortening they have recorded. This approach allows modeling of isolated terraces or growth strata. We apply this method to the study of two fault tip folds in the Tien Shan, the Yakeng and Anjihai anticlines, documenting their deformation history over the past 6–7 Myr. We show that the modern shortening rates can be estimated from the width of the fold topography provided that the sedimentation rate is known, yielding respective rates of 2.15 and 1.12 mm/yr across Yakeng and Anjihai, consistent with the deformation recorded by fluvial and alluvial terraces. This study demonstrates that the shortening rates across both folds accelerated significantly since the onset of folding. It also illustrates the usefulness of a simple geometric folding model and highlights the importance of considering local interactions between tectonic deformation, sedimentation, and erosion

Structurally constrained protein evolution: results from a lattice simulation

We simulate the evolution of a protein-like sequence subject to point mutations, imposing conservation of the ground state, thermodynamic stability and fast folding. Our model is aimed at describing neutral evolution of natural proteins. We use a cubic lattice model of the protein structure and test the neutrality conditions by extensive Monte Carlo simulations. We observe that sequence space is traversed by neutral networks, i.e. sets of sequences with the same fold connected by point mutations. Typical pairs of sequences on a neutral network are nearly as different as randomly chosen sequences. The fraction of neutral neighbors has strong sequence to sequence variations, which influence the rate of neutral evolution. In this paper we study the thermodynamic stability of different protein sequences. We relate the high variability of the fraction of neutral mutations to the complex energy landscape within a neutral network, arguing that valleys in this landscape are associated to high values of the neutral mutation rate. We find that when a point mutation produces a sequence with a new ground state, this is likely to have a low stability. Thus we tentatively conjecture that neutral networks of different structures are typically well separated in sequence space. This results indicates that changing significantly a protein structure through a biologically acceptable chain of point mutations is a rare, although possible, event.Comment: added reference, to appear on European Physical Journal

The Unusual 3D Interplay of Basement Fault Reactivation and Fault-Propagation-Fold Development: A Case Study of the Laramide-age Stillwell Anticline, West Texas (USA)

Subsurface fault geometries have a systematic influence on folds formed above those faults. We use the extraordinarily well-exposed fold geometries of the Laramide-age Stillwell anticline in west Texas (USA) to develop a strain-predictive model of fault-propagation fold formation. The anticline is a 10-km long, NW-trending, NE-vergent, asymmetric fold system with an axis that displays a map-view left-stepping, en echelon pattern. We integrated field observations, geologic and structural data, cross-sections, and 2D kinematic modeling to establish an unusual 3D two-stage model of contractional fold formation, including: 1) reverse reactivation of a pre-existing, NW-striking, SW-dipping, left-stepping, en echelon normal fault system in Paleozoic basement rocks to generate monoclinal flexures in overlying layered Cretaceous carbonate rocks; and 2) the formation of a subsequent flat-ramp fault system that propagated horizontally along a mechanically-weak, clay-rich Cretaceous unit before ramping up at the hinge of the pre-existing monocline system. Strain is focused within the forelimb of the system, in front of the propagating fault tip, and is accommodated by a combination of interlayer slip, flat-ramp faulting, and fracturing proximal to planes of slip. This strain predictive model can be applied to similar, less-well-exposed contractional systems worldwide and provides a new, unusual example of Laramide-age contractional deformation

ALMA Thermal Observations of Europa

We present four daytime thermal images of Europa taken with the Atacama Large Millimeter Array. Together, these images comprise the first spatially resolved thermal dataset with complete coverage of Europa's surface. The resulting brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a typical linear resolution of roughly 200 km. At this resolution, the images capture spatially localized thermal variations on the scale of geologic and compositional units. We use a global thermal model of Europa to simulate the ALMA observations in order to investigate the thermal structure visible in the data. Comparisons between the data and model images suggest that the large-scale daytime thermal structure on Europa largely results from bolometric albedo variations across the surface. Using bolometric albedos extrapolated from Voyager measurements, a homogenous model reproduces these patterns well, but localized discrepancies exist. These discrepancies can be largely explained by spatial inhomogeneity of the surface thermal properties. Thus, we use the four ALMA images to create maps of the surface thermal inertia and emissivity at our ALMA wavelength. From these maps, we identify a region of either particularly high thermal inertia or low emissivity near 90 degrees West and 23 degrees North, which appears anomalously cold in two of our images.Comment: 9 pages, 3 figures, accepted for publication in the Astronomical Journa

APPLICATION OF FRACTAL MODELING BASED ON REMOTE SENSING DATA FOR DETECTING IRON MINERALIZATION IN DEHSHIR–BAFT FAULT, WEST OF CENTRAL IRAN

Part of Dehshir–Baft Fault is located on the 1:100000 Sarvbala geological sheet west of Yazd Province in Iran on the Urmia–Dokhtar magmatic–mineralization zone. Regions with iron mineralization potential on this sheet were detected by identifying alterations and fault trends by processing ASTER satellite images. Images were processed using the false color composite (FCC), Crosta, LS-Fit, and spectral angle mapper (SAM) methods to identify iron oxide, argillic, ­­­­propylitic, and phyllic alterations. To find out the role of faults and lineaments in mineralization, the general faulting trend on this sheet was extracted by relief shading on the digital elevation model (DEM), and the fault zones were examined through field operations. Regions with high iron potential were identified by integrating the fault layers, alterations, and mineralization-related geological units in ArcGIS. The identified regions were then validated through field operations. The relationship between the distance of iron oxide alterations obtained from the LS-Fit method with the main fault was evaluated by the fractal method. The results showed the location and more significant relationship of iron potential with faults in the south and southwest of Sarvbala sheet than other regions.Parte da falha de Dehshir – Baft está localizada na folha geológica Sarvbala 1: 100.000 a oeste da província de Yazd, no Irã, na zona de mineração magmática Urmia – Dokhtar. A pesquisa conduzida buscou indetificar regiões com potencial de mineração de ferro nesta folha a partir da detecção e identificação de alterações e tendências de falha pelo processamento de imagens de satélite do instrumento ASTER. As imagens foram processadas usando os métodos de composição falsa cor (FCC), Crosta, LS-Fit e mapemaneto de ângulo espectral (SAM) para identificar alterações de óxido de ferro, argílico, propilítico e fílico na área. Para descobrir o papel das falhas e lineamentos na mineração, a tendência geral de falhas nesta folha foram obtidas com a elaboração do sombreamento do relevo no Modelo Digital de Elevação (DEM), e as zonas de falha foram examinadas por meio de verificações de campo. Regiões com alto potencial de ferro foram identificadas através da integração das camadas de falha, alterações e unidades geológicas relacionadas à mineração com o uso do programa ArcGIS. As regiões identificadas foram então validadas in loco. A relação entre a distância das alterações do óxido de ferro obtida pelo método LS-Fit com a falha principal foi avaliada pelo método fractal. Os resultados mostraram a localização e a relação mais significativa do potencial de ferro com as falhas no sul e sudoeste da folha do mapa geológico de Sarvbala do que em outras regiões

MEVTV Workshop on Tectonic Features on Mars

The state of knowledge of tectonic features on Mars was determined and kinematic and mechanical models were assessed for their origin. Three sessions were held: wrinkle ridges and compressional structure; strike-slip faults; and extensional structures. Each session began with an overview of the features under discussion. In the case of wrinkle ridges and extensional structures, the overview was followed by keynote addresses by specialists working on similar structures on the Earth. The first session of the workshop focused on the controversy over the relative importance of folding, faulting, and intrusive volcanism in the origin of wrinkle ridges. The session ended with discussions of the origin of compressional flank structures associated with Martian volcanoes and the relationship between the volcanic complexes and the inferred regional stress field. The second day of the workshop began with the presentation and discussion of evidence for strike-slip faults on Mars at various scales. In the last session, the discussion of extensional structures ranged from the origin of grabens, tension cracks, and pit-crater chains to the origin of Valles Marineris canyons. Shear and tensile modes of brittle failure in the formation of extensional features and the role of these failure modes in the formation of pit-crater chains and the canyons of Valles Marineris were debated. The relationship of extensional features to other surface processes, such as carbonate dissolution (karst) were also discussed