High Poisson's Ratio Research Articles

Moho depth and Poisson's ratio in the Western-Central Alps from receiver functions

Current knowledge about deep crustal structure of the Alpine orogen has mainly been derived from P-wave velocity models obtained from active and passive seismic experiments. A complementary S-wave model to provide lithological constraints necessary for unique structural interpretation has been missing to date. In this paper, we present important new information on S-wave velocity model in the Alps. We applied the receiver function method using 6 yr of high quality data from 61 permanent and temporary stations sampling the Western—Central Alps. We determined first-order crustal features Moho depth (H) and average Vp/Vs ratio (κ) with the H–κ stacking technique that uses timing of direct and multiple P-to-S converted phases from the Moho interface. Synthetic tests reveal a dipping Moho interface, expected beneath an orogen, causes a systematic bias of H and κ potentially leading to misinterpretation. We thus applied corrections determined from synthetic data to remove the bias, providing better fit of recovered Moho depths with active seismic estimates. For each site, we also obtained independent H and κ estimates based on the timing of the strong Ps-phase. Our results show a gently south—southeast dipping European Moho at a depth of ∼24–30 km beneath the Northern Alpine Foreland, steepening rapidly towards the Europe—Africa suture zone to reach a maximum depth of ∼55 km. South of the suture, the Moho of the Adriatic crust, promontory of the African plate, is at ∼35–45 km depth. In the previously ill-constrained Western Alps, we found the European Moho at ∼30 km depth beneath the more external units dipping east—northeast to reach ∼50–55 km in the inner core of the Alps. The Poisson's ratio clearly correlates with the tectonic units that comprise the Alps. Average crustal values in the European Alpine Foreland are close to 0.25. In the Alps, we observe low values (0.22) in the highly deformed nappes of the Mesozoic Helvetic and Southern Alps indicating a thickening of felsic upper-crustal material. In contrast, the Poisson's ratio is significantly higher (0.26) in the Penninic and Austroalpine units near the suture zone. This rapid and significant change marks a clear rupture between the Alpine forelands and the suture domain. We assign this high Poisson's ratio to doubling of mafic lower crust consistent with results from previous active seismic experiments. A continuation of the lower crustal wedge into the central part of the Western Alps, however, seems unlikely based on low observed Poisson's ratios.

The 2007 Niigata earthquake: Effect of arc magma and fluids

To clarify the generation mechanism of large crustal earthquakes in the Amur–Okhotsk plate boundary, we determined high-resolution 3D seismic velocity ( V p, V s) and Poisson's ratio structures in Niigata, Northeast Japan using a large number of P- and S-wave arrival times from the aftershocks of the 2004 and 2007 Niigata earthquakes as well as many intermediate-depth earthquakes in this area. Our results show that the Niigata mainshocks occurred around zones of low-velocity and high-Poisson's ratio, which suggest that fluids may have influenced the nucleation and rupture processes of the 2004 and 2007 Niigata earthquakes. A zone with pronounced low-velocity and high Poisson's ratio is revealed under the source areas of the 2004 and 2007 Niigata earthquakes in the lower crust and uppermost mantle, which may reflect the arc magma and fluids ascending from the upper-mantle wedge. These results indicate that the generation of the 2004 and 2007 Niigata earthquakes was affected by the ascending magma and fluids released by the dehydration process of the subducting Pacific slab.

Chalk porosity and sonic velocity versus burial depth: Influence of fluid pressure, hydrocarbons, and mineralogy

Seventy chalk samples from four formations in the overpressured Danish central North Sea have been analyzed to investigate how correlations of porosity and sonic velocity with burial depth are affected by varying mineralogy, fluid pressure, and early introduction of petroleum. The results show that porosity and sonic velocity follow the most consistent depth trends when fluid pressure and pore-volume compressibility are considered. Quartz content up to 10% has no marked effect, but more than 5% clay causes lower porosity and velocity. The mineralogical effect differs between P-wave and shear velocity so that smectite-bearing chalk has a high Poisson's ratio in the water-saturated case, but a low value in the dry case. Oil-bearing chalk has up to 25 units higher porosity than water-saturated chalk at similar depth but similar velocity, probably because hydrocarbons prevent pore-filling cementation but not pore-structure stiffening cementation in this presumably water-wet chalk. These results should improve the modeling of chalk background velocity for seismic inversion analysis. When describing the porosity-reducing process, pore-volume compressibility should probably be disregarded when correcting for fluid pressure because the cementing ions originate from stylolites, which are mechanically similar to fractures. We find that cementation occurs over a relatively short depth interval.

Tomographic evidence for the subducting oceanic crust and forearc mantle serpentinization under Kyushu, Japan

We determined high-resolution three-dimensional P- and S-wave velocity (Vp, Vs) structures beneath Kyushu in Southwest Japan using 177,500 P and 174,025 S wave arrival times from 8515 local earthquakes. A Poisson's ratio structure was derived from the obtained Vp and Vs values. Our results show that significant low-Vp, low-Vs and high Poisson's ratio zones are extensively distributed along the volcanic front in the uppermost mantle, which extend and dip toward the back-arc side in the mantle wedge. In the crust, low-Vp, low-Vs and high Poisson's ratio anomalies exist beneath the active volcanoes. The subducting Philippine Sea slab is clearly imaged as a high-Vp, high-Vs and low Poisson's ratio zone from the Nankai Trough to the back-arc. A thin low-velocity zone is detected above the subducting Philippine Sea slab in the mantle wedge, and earthquakes in the upper mantle are distributed along the transition zone between this thin low-velocity zone and the high-velocity Philippine Sea slab, which may imply that oceanic crust exists on the top of the slab and the forearc mantle wedge is serpentinized due to the slab dehydration. The seismic velocity of the subducting oceanic crust with basaltic or gabbroic composition is lower than that of the mantle according to the previous studies. The serpentinization process could also dramatically reduce the seismic velocity in the forearc mantle wedge.

Low-temperature acoustic properties and quasiharmonic analysis for Cu-based bulk metallic glasses

Low-temperature elastic constant ${C}_{ij}(T)$ measurements for ${\mathrm{Cu}}_{60}{\mathrm{Zr}}_{30}{\mathrm{Ti}}_{10}$ and ${\mathrm{Cu}}_{60}{\mathrm{Hf}}_{25}{\mathrm{Ti}}_{15}$ bulk metallic glasses (BMGs) have been carried out to clarify their acoustic properties including a nonlinear interaction term. The BMGs show remarkably low shear to bulk modulus ratio ${C}_{44}∕B$ or equivalently high Poisson's ratio $\ensuremath{\nu}$ compared with the corresponding crystalline states. The ${C}_{ij}(T)$ behaviors are well described by Varshni's formula [Phys. Rev. B 2, 3952 (1970)] and estimated Einstein temperatures suggested significant softening in the transverse-mode acoustic phonon. Mean Gr\"uneisen parameters $\ensuremath{\gamma}$ derived from $dB∕dT$ slopes become almost identical with those of crystalline Cu. Our theoretical analysis based on inhomogeneous microstructure model successively explains the elastic constants and characteristic features of the BMGs within a framework of quasiharmonic thermodynamics, suggesting that microstructural inhomogeneity plays a dominant role in the BMGs.

Structure of the crust beneath the southeastern Tibetan Plateau from teleseismic receiver functions

Southeastern Tibet marks the site of presumed clockwise rotation of the crust due to the India–Eurasian collision and abutment against the stable Sichuan basin and South China block. Knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region. Here, we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method. We find that the crustal thickness decreases gradually from the Tibetan Plateau proper to the Sichuan basin and Yangtze platform but that significant (intra-)crustal heterogeneity exists on shorter lateral scales (<1000 km). Most receiver functions reveal a time shift of ∼0.2 s in the direct P arrival and negative phases between 0 and 5 s after the first arrival. Inversion of the receiver functions yields S-velocity profiles marked by near-surface and intra-crustal low-velocity zones (IC-LVZs). The shallow low-velocity zones are consistent with the wide distribution of thick surface sedimentary layers. The IC-LVZ varies laterally in depth and strength; it becomes thinner toward the east and southeast and is absent in the Sichuan basin and the southern part of the Yangtze platform. Results from slant-stacking analysis show a concomitant decrease in crust thickness from ∼60 km in the Songpan-Ganze fold system to ∼46 km in the Sichuan basin and ∼40 km in the Yangtze platform. High Poisson's ratios (>0.30) are detected beneath the southeastern margin of Tibet but in the Sichuan basin and southeastern Yangtze platform the values are close to the global average. Combined with high regional heat flow and independent evidence for mid-crustal layers of high (electric) conductivity, the large intra-crustal S-wave velocity reduction (12–19%) and the intermediate-to-high average crustal Poisson's ratios are consistent with partial melt in the crust beneath parts of southeastern Tibet. These results could be used in support of deformation models involving intra-crustal flow, with the caveat that significant lateral variation in location and strength of this flow may occur.

Simulation of high tensile Poisson's ratios of articular cartilage with a finite element fibril-reinforced hyperelastic model

Analyses with a finite element fibril-reinforced hyperelastic model were undertaken in this study to simulate high tensile Poisson's ratios that have been consistently documented in experimental studies of articular cartilage. The solid phase was represented by an isotropic matrix reinforced with four sets of fibrils, two of them aligned in orthogonal directions and two oblique fibrils in a symmetric configuration respect to the orthogonal axes. Two distinct hyperelastic functions were used to represent the matrix and the fibrils. Results of the analyses showed that only by considering non-orthogonal fibrils was it possible to represent Poisson's ratios higher than one. Constrains in the grips and finite deformations played a minor role in the calculated Poisson's ratio. This study also showed that the model with oblique fibrils at 45° was able to represent significant differences in Poisson's ratios near 1 documented in experimental studies. However, even considering constrains in the grips, this model was not capable to simulate Poisson's ratios near 2 that have been reported in other studies. The study also confirmed that only with a high relation between the stiffness of the fibers and that of the matrix was it possible to obtain high Poisson's ratios for the tissue. Results suggest that analytical models with a finite number of fibrils are appropriate to represent main mechanical effects of articular cartilage.

Crustal thicknesses and Poisson's ratios in China by joint analysis of teleseismic receiver functions and Rayleigh wave dispersion

A new grid search scheme, which extends the stacking H‐κ algorithm to multi‐layered crustal models and fits observed dispersion of surface wave group velocity simultaneously, is proposed to estimate the thickness, Poisson's ratio, and average P wave speed of the crust. We first apply it to a synthetic data of a 2‐layered crustal model. Then we show the results analyzing records from 45 permanent broadband seismic stations in China. The estimates at six stations agree well with results from deep seismic sounding profiles. The crustal thicknesses agree in general with the Crust 2.0 model. We find that the Poisson's ratio in the Yangtze platform is rather low compared with the other two platforms. The stations along the southeast coast of China have higher Poisson's ratios. The Poisson's ratio of the whole region tends to increase as the average P‐wave velocity.

Free volume and elastic properties changes in Cu–Zr–Ti–Pd bulk glassy alloy on heating

The variation of free volume and elastic properties of the Cu 55Zr 30Ti 10Pd 5 glassy alloy on heating was studied. The structure changes on heating were studied by synchrotron X-ray diffraction, differential scanning and isothermal calorimetries. The studied glassy alloy shows a rather high Poisson's ratio exceeding 0.42 which is maintained after the structure relaxation and primary devitrification. Young's and Shear modules decrease upon primary devitrification while Bulk modulus exhibits a maximum after structural relaxation.

Exploration of high and negative Poisson's ratio elastomer‐matrix laminates

AbstractElastomer‐matrix composites show promise for high Poisson's ratio and negative Poisson's ratio (auxetic) applications due to high orthotropy. There are approximately five orders of magnitude between the axial stiffness of high modulus graphite fibres and the stiffness of low durometer elastomers. Although the maximum Poisson's ratio for isotropic elastomers is 0.5, it is easily shown that inplane Poisson's ratios twice unity can be obtained with a graphite/epoxy angle‐ply laminate at 25°. Chou and others have predicted inplane Poisson's ratios greater than 7 for certain cord‐rubber combinations. Peel previously predicted inplane Poisson's ratios higher than 32 and less than –60. Preliminary experimental results have produced inplane Poisson's ratios as high as 14. Certain combinations of un‐balanced highly orthotropic laminates may also produce inplane negative Poisson's ratios. Inplane Poisson's ratios, experimentally obtained from two laminate configurations with approximately the same axial stiffness are compared. A symmetric, balanced laminate produced an inplane Poisson's ratio of 3.7; while an unbalanced laminate with an equivalent axial stiffness produced an average inplane Poisson's ratio of –1.5. Certain high and negative Poisson's ratio elastomer‐matrix laminates appear to have quasi anti‐symmetric relationships about 0°, although laminate designers may consider dual angle‐ply laminates to be the more likely counterpart to the unbalanced dual angle auxetic laminates. Unbalanced symmetric laminates experience significantly more inplane shear deformation when axially loaded than their balanced counterparts. The high shear may be desirable for damping applications, but less desirable otherwise. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Preface: phys. stat. sol. (b) 244/3

The 21st Winterschool on Electronic Properties of Novel Materials (IWEPNM 2007) took place from 10 March to 17 March 2007. It continued the tradition of winterschools of this type in Kirchberg/Tirol in its well-known atmosphere of collegiality and emphasis on scientific exchange between young and experienced scientists. The sessions at the IWEPNM 2007 focused on quantum information, carbon nanostructure synthesis, purification and separation, the characterization and properties of carbon nanostructures, fullerenes, endohedrals, and fullerides, excitons in carbon nanotubes, the chemical treatment of carbon nanotubes, nanotube filling and double-walled nanotubes, graphite and graphene, non-carbonaceous nanostructures, electron and heat transport in carbon nanostructures, composites with carbon nanotubes, and on theory and applications of these materials. This proceedings volume is divided into according sections. The program of the Winterschool was composed of invited oral presentations, poster presentations and mini-workshops. The oral presentations were scheduled in morning and evening sessions, the mini-workshops took place during the afternoons, and the posters were presented and discussed in two late-evening sessions. In 2007 the Winterschool celebrated an anniversary: It had been of taking place for the 20th time at the Hotel Sonnenalp, a hotel ideally suited for the close interactions of international participants from many countries. We are grateful to the manager of Hotel Sonnenalp, Frau Edith Mayer, and her staff for the local arrangements as well as for her patience with many special requests during the meeting. We owe special thanks to the hotel staff for their careful organization of the celebration. The event benefited substantially from support of the Universitat Wien and the Verein zur Forderung der Winterschulen in Kirchberg, as well as from numerous industrial sponsors. We greatly appreciate their financial contribution without which the meeting would have hardly become possible. Finally, special acknowledgments go to all contributors of the IWEPNM 2007 and to the authors of this volume, the proceedings of the Winterschool. Viera Skakalova was instrumental in compiling and editing the proceedings. In the name of all participants who have enjoyed the Winterschools since 1985 we express special thanks to Hans Kuzmany for his outstanding engagement in organizing the IWEP for so many years. His experience and advice will be needed for future Winterschools. The next Winterschool in this series will take place from 1 March to 8 March 2008, again in Kirchberg/Tirol, and will be organized by Christian Thomsen from Berlin. Wien, Darmstadt, Stuttgart, Berlin, 2007

Low Temperature Elastic Properties of CuZrTi Bulk Metallic Glass

Temperature dependent elastic constants C ij (T) of Cu 60 Zr 30 Ti 10 bulk metallic glass (BMG) have been studied using MHz frequency range electromagnetic acoustic resonance (EMAR) from 4.5 to 300 K. At ambient temperature, the BMG shows low shear/bulk modulus ratio (or equivalently high Poisson ratio) compared with that of corresponding crystalline state dues to the dense random packed glassy structure. Analysis of C,j(T) based on the Einstein type lattice vibration model revealed the notable softening in transverse mode acoustic phonons. This unusual vibrational property suggests the existence of liquid like weakly bonded region in the BMG.

Glass-structure changes in tilt-cast Zr–Cu–Al glassy alloys

In order to clarify the relationship between the glass structure and mechanical properties, splat-cooled and tilt-cast Zr–Cu–Al glassy alloys were studied. The glass structure difference was estimated considering thermal factors (glass-transition temperature, crystallization temperature, etc.) and the volume change from the as-cast state to fully relaxed state. The compositional dependence of the tensile strength and Charpy-impact energy is closely related to that of the glass-transition temperature and volume change. We also examined the Poisson's ratio to find out ductile glassy alloys. As a result, solvent(Zr)-enriched off-eutectic glassy alloys show rather high Poisson's ratios.

Velocity determination for pore-pressure prediction

Overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth (Dutta, 2002): (1) higher porosities, (2) lower bulk densities, (3) lower effective stresses, (4) higher temperatures, (5) lower interval velocities, and (6) higher Poisson's ratios.

Three‐dimensional attenuation (Qs) structure beneath the Kanto district, Japan, as inferred from strong motion records

The three‐dimensional (3D) S‐wave attenuation (Qs) structure beneath the Kanto plain, where the Pacific and Philippine Sea plates subduct, was estimated using strong‐motion records of the K‐NET and KiK‐net. In addition to several low‐Qs zones corresponding to the volcanic front, a large NW–SE trending low‐Qs zone is estimated under the non‐volcanic Kanto area at depths of 20–60 km. This zone corresponds to a previously identified low‐velocity (both Vp and Vs) zone with a high Poisson's ratio at 40‐km depth; it further indicates a wedge immediately above the subducting Philippine Sea plate. Predicted seismic ground motions using the estimated 3D attenuation structure is very similar to the actually recorded by recent earthquake on July 2005 (M = 6).

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Seismic data from both explosive and earthquake sources have been used to model the crustal and upper-mantle velocity structure beneath the Taupo Volcanic Zone (TVZ), an active backarc basin in central North Island, New Zealand. Volcanic sediments with P-wave velocities of 2.0–3.5 km s−1 reach a maximum thickness of 3 km beneath the central TVZ. Underlying these sediments to 16 km depth is material with velocities of 5.0–6.5 km s−1, interpreted as quartzo-feldspathic crust. East and west of the TVZ, crust with similar velocities is found to depths of 30 and 25 km, respectively. Beneath the TVZ, material with P-wave velocities of 6.9–7.3 km s−1 is found from 16 to 30 km depth and is interpreted as heavily intruded or underplated lower crust. The base of the crust at 30 km depth under the TVZ is marked by a strong seismic reflector, interpreted as the Moho. Modelling of arrivals from deep (>40 km) earthquakes near the top of the underlying subducting Pacific Plate reveals a region with low mantle velocities of 7.4–7.8 km s−1 beneath the crust of the TVZ. This region of low mantle velocities is best explained by the presence of partially hydrated upper mantle, resulting from dehydration of hydrous minerals (e.g. serpentinite) carried down by the underlying subducting plate. Within the lower crust beneath the TVZ, a region of high (0.34) Poisson's ratio is observed, indicating the presence of at least 1 per cent partial melt. This melt probably fractionates and assimilates crustal material before some of it migrates into the upper crust, where it provides a source for the voluminous rhyolitic magmas of the TVZ.

A tomographic image of upper crustal structure using P and S wave seismic refraction data in the southern granulite terrain (SGT), India

We present a 2‐D tomographic P and S wave velocity (Vp and Vs) image with Vp/Vs ratios along N‐S trending 220 km long deep seismic profile acquired in 2005, which traverses across major shear and tectonically disturbed zones in southern granulite terrain (SGT), India. The 2‐D velocity model constrained down to maximum 8 km depth shows velocity anomalies (&gt;0.2 km/s) beneath major shear zones with good spatial resolution (&gt;0.05 km/s). The presence of high Vp (6.3–6.5 km/s), Vs (3.5–3.8 km/s), Vp/Vs (&gt;1.75) and Poisson's ratio (0.25–0.29) indicate significant compositional changes of rocks at shallow depths (0.5 to 8 km) reveal rapid crustal exhumation of mid to lower crustal rocks. This crustal exhumation could be responsible due to Pan‐African tectonothermal activity during Neoproterozoic period.

Hybrid and enhanced finite element methods for problems of soil consolidation

AbstractHybrid and enhanced finite element methods with bi‐linear interpolations for both the solid displacements and the pore fluid pressures are derived based on mixed variational principles for problems of elastic soil consolidation. Both plane strain and axisymmetric problems are studied. It is found that by choosing appropriate interpolation of enhanced strains in the enhanced method, and by choosing appropriate interpolations of strains, effective stresses and enhanced strains in the hybrid method, the oscillations of nodal pore pressures can be eliminated. Several numerical examples demonstrating the capability and performance of the enhanced and hybrid finite element methods are presented. It is also shown that for some situations, such as problems involving high Poisson's ratio and in other related problems where bending effects are evident, the performance of the enhanced and hybrid methods are superior to that of the conventional displacement‐based method. The results from the hybrid method are better than those from the enhanced method for some situations, such as problems in which soil permeability is variable or discontinuous within elements. Since all the element parameters except the nodal displacements and nodal pore pressures are assumed in the element level and can be eliminated by static condensation, the implementations of the enhanced method and the hybrid method are basically the same as the conventional displacement‐based finite element method. The present enhanced method and hybrid method can be easily extended to non‐linear consolidation problems. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Crustal structure of the northeastern margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin

The 1000-km-long Darlag–Lanzhou–Jingbian seismic refraction profile is located in the NE margin of the Tibetan plateau. This profile crosses the northern Songpan-Ganzi terrane, the Qinling-Qilian fold system, the Haiyuan arcuate tectonic region, and the stable Ordos basin. The P-wave and S-wave velocity structure and Poisson's ratios reveal many significant characteristics in the profile. The crustal thickness increases from northeast to southwest. The average crustal thickness observed increases from 42 km in the Ordos basin to 63 km in the Songpan-Ganzi terrane. The crust becomes obviously thicker south of the Haiyuan fault and beneath the West-Qinlin Shan. The crustal velocities have significant variations along the profile. The average P-wave velocities for the crystalline crust vary between 6.3 and 6.4 km/s. Beneath the Songpan-Ganzi terrane, West-Qinling Shan, and Haiyuan arcuate tectonic region P-wave velocities of 6.3 km/s are 0.15 km/s lower than the worldwide average of 6.45 km/s. North of the Kunlun fault, with exclusion of the Haiyuan arcuate tectonic region, the average P-wave velocity is 6.4 km/s and only 0.5 km/s lower than the worldwide average. A combination of the P-wave velocity and Poisson's ratio suggests that the crust is dominantly felsic in composition with an intermediate composition at the base. A mafic lower crust is absent in the NE margin of the Tibetan plateau from the Songpan-Ganzi terrane to the Ordos basin. There are low velocity zones in the West-Qinling Shan and the Haiyuan arcuate tectonic region. The low velocity zones have low S-wave velocities and high Poisson's ratios, so it is possible these zones are due to partial melting. The crust is divided into two layers, the upper and the lower crust, with crustal thickening mainly in the lower crust as the NE Tibetan plateau is approached. The results in the study show that the thickness of the lower crust increases from 22 to 38 km as the crustal thickness increases from 42 km in the Ordos basin to 63 km in the Songpan-Ganzi terrane south of the Kunlun fault. Both the Conrad discontinuity and Moho in the West-Qinling Shan and in the Haiyuan arcuate tectonic region are laminated interfaces, implying intense tectonic activity. The arcuate faults and large earthquakes in the Haiyuan arcuate tectonic region are the result of interaction between the Tibetan plateau and the Sino–Korean and Gobi Ala Shan platforms.

Iron-Rich Post-Perovskite and the Origin of Ultralow-Velocity Zones

The boundary layer between the crystalline silicate lower mantle and the liquid iron core contains regions with ultralow seismic velocities. Such low compressional and shear wave velocities and high Poisson's ratio are also observed experimentally in post-perovskite silicate phase containing up to 40 mol% FeSiO3 endmember. The iron-rich post-perovskite silicate is stable at the pressure-temperature and chemical environment of the core-mantle boundary and can be formed by core-mantle reaction. Mantle dynamics may lead to further accumulation of this material into the ultralow-velocity patches that are observable by seismology.