Wedge Deformation Research Articles

Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syn-tectonic conglomerates in the Spanish Pyrenees

We present new geochronologic data illuminating the tectonic and erosional history of the orogenic wedge exposed in the south-central Pyrenees, Spain. We interpret illite-age analyses from four fault gouges that record thrust-belt development and document the importance of out-of-sequence thrusting. Fault activity occurs in pulses, with slip occurring contemporaneously on multiple faults throughout the wedge. New apatite fission-track data from syn-orogenic sediments of the Sis Conglomerate body reveal ages of 48 to 42 Ma, with no consistent variation upsection in strata deposited from 41 to 30 Ma. We interpret these data, as well as thermal modeling of track-length distributions, to imply rapid cooling in the interior of the Pyrenean wedge during the Middle Eocene. The record of fault activity and erosion suggests that orogenic wedges may not evolve in a steady fashion, but generally exhibit significant changes in rates of deformation and exhumation. The observed correlation in the timing of tectonism and erosional exhumation provides evidence for links between tectonic and surface processes.

Orogenic-wedge deformation and potential for great earthquakes in the central Andean backarc

Subduction of the Nazca plate beneath South America has driven the growth of the Andes Mountains. Subduction has routinely generated earthquakes larger than magnitude 8.0 along the western margin of the mountain belt 1 , but the potential size of less frequent earthquakes in the eastern, backarc margin is unknown. Continued support of the high Andean Plateau at the centre of the Andes can be explained only if deformation of the backarc margin is ongoing 2‐4 . Here we present GPS data that record surface motions in the Subandean ranges that are part of the backarc margin. We find that the velocity of surface movement decreases sharply from west to east across the Subandean ranges. We suggest that a subhorizontal fault underlying the ranges slips freely at depth in the west, but is locked for up to 100 km in shallower sections further east. Analysis of fault scarps formed where the subhorizontal fault intersects the surface indicates that the fault has generated repeated large earthquakes. We suggest that rupture of the entire locked section of the fault could generate an earthquake of magnitude 8.7‐8.9. We attribute the large seismic potential to the unusual width of the Subandean ranges, and suggest that deformation of the Subandean ranges, at a rate unmatched by erosion, causes the mountain range to widen. The central Andean Plateau (AP) is a bilaterally symmetric plateau of 4;000m average elevation (Fig. 1). Although AP uplift scenarios are currently debated 5,6 it is generally accepted that the backarc orogenic wedge on the AP’s east flank, comprising the Eastern Cordillera (EC), Inter-Andean zone (IAZ), and Subandes (SA), has contracted by more than 250km since 45Myr ago (refs 79). Wedge deformation has been facilitated by the presence

Frontal wedge deformation near the source region of the 2011 Tohoku-Oki earthquake

[1] We report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 Tohoku-Oki earthquake. The uplift was measured by an ocean-bottom pressure gauge installed before the earthquake on a frontal wedge, which formed an uplift system near the Japan Trench. Horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake. The average displacements at the frontal wedge were 58 m east and 74 m east-southeast. These results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary. The estimated magnitude of the slip along the main fault was 80 m near the trench. Our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern Japan.

The development of a clinical decision making algorithm for detection of osteoporotic vertebral compression fracture or wedge deformity

The clinical diagnosis of an osteoporotic vertebral compression fracture (OVCF) is challenging and requires detailed assessment using comprehensive imaging methods. Further complicating matter is that the clinical sequelae associated with OVCF typically involves asymptomatic findings and variable pain patterns. The purpose of this study was to identify clinical characteristics and assessment findings that were associated with a diagnosis of OVCF. The study evaluated routine clinical findings in over 1400 subjects seen at an adult spine surgery clinic for thoracolumbar spine-related conditions within the years 2005–2009. All patients underwent a standardized clinical examination that included a self-report, observational, physical examination and imaging assessment. The diagnosis of OVCF was made after assessment of radiographic findings in sagittal alignment, vertebral body compression, and spinal canal dimensions. Data from the patient history and observational findings were then statistically analyzed and compared between those patients with a diagnosis of OVCF and those with an alternative diagnosis. Based on the results, a diagnostic support tool was created to predict the likelihood of OVCF. The most diagnostic combination included a cluster of: (1) age > 52 years; (2) no presence of leg pain; (3) body mass index ≤ 22; (4) does not exercise regularly; and (5) female gender. A finding of two of five positive tests or less demonstrated high sensitivity of 0.95 (95% CI 5 0.83–0.99) and low negative likelihood ratio of 0.16 (95% CI = 0.04–0.51), providing moderate value to rule out OVCF. Four of five yielded a positive likelihood ratio (LR+) of 9.6 (95% CI = 3.7–14.9) providing moderate value in ruling in the diagnosis of OVCF. Further validation is necessary prospectively to determine the value of these findings on a disparate sample of patients in other unique environments.

A novel non-bridging external fixator construct versus volar angular stable plating for the fixation of intra-articular fractures of the distal radius—A biomechanical study

Non-bridging external fixation has recently been introduced as an alternative to volar angular stable plating for the fixation of unstable intra-articular distal radial fractures. The purpose of this study was to biomechanically compare a new non-bridging external fixator construct to volar angular stable plate fixation in a dorsally comminuted intra-articular fracture model of the distal radius. Five pairs of fresh frozen human cadaveric radii were randomly supplied with either a non-bridging external fixator or a stainless steel volar locking plate. A three-fragmental AO 23-C2.1 fracture was created by removing a 15 degrees dorsal wedge with remaining volar cortical contact and by an intra-articular osteotomy lateral to the lister-tubercle. Physiological load transfer via the wrist was simulated by means of a custom-made seesaw. For biomechanical testing, the bones were loaded in cyclic axial compression. Starting at 100N, the load was monotonically increased at 0.025 degrees N per cycle until failure of the construct. Motion of the lunate and scaphoid fragments with respect to the radial diaphysis was acquired by optical three-dimensional (3D) motion tracking. Plastic wedge deformation was determined after 2000, 4000 and 6000 cycles. The amplitude of wedge motion at the beginning of the test as a measure for construct stiffness was significantly lower for the fixator group (P=0.003, power=0.99). Plastic wedge deformation after 2000, 4000 and 6000 cycles was found significantly lower for the external fixator (repeated measures analysis of variance (ANOVA), P=0.009, power=0.86). Displacement of the intra-articular gap was found below 0.6mm (mean) for both groups (P>0.05). The study revealed superior biomechanical properties of the proposed non-bridging external fixation compared to volar locked plating in an unstable intra-articular fracture model with volar cortical support. However, both fixation techniques seem to apply sufficient stabilisation to restore and retain anatomy after fracture of the most distal part of the radius and should be individually chosen according to distinct criteria.

Understanding kinematic data from the Moine thrust zone in terms of a kinematics-based mathematical model of deforming thrust wedges

A salient–recess pair along the Moine thrust zone exhibits significant lateral, kinematic variations. Specifically, the more steeply dipping portion of the thrust surface, associated with the recess, shows evidence for greater strain magnitudes and more out-of-the-plane motion than the adjoining salient. Additionally, a subset of the grain-shape data has grain-shape approximations with their long axes oriented perpendicular to the regional transport direction. To more fully understand these kinematic features, we developed a kinematics-based mathematical model of thrust wedge deformation. Our numerical model predicts an increase in strain magnitude as well as non-plane-strain flattening in the region of a thrust ramp, consistent with the strain patterns observed within the recess along the Moine thrust zone. Furthermore, in the absence of a lateral-confining boundary condition, much of the model thrust wedge experiences transport-perpendicular, maximum extension except for the region closest to the thrust where simple-shear deformation is dominant. Using our numerical model, we predict the amount of lateral-confining strain needed to induce plane-strain deformation ( ɛ ps) as well as the amount of lateral-confining strain necessary to make the long axis of the strain ellipsoid parallel with the transport direction ( ɛ parallel). We have found that the incremental ɛ parallel can be as much as 42% of the incremental strain magnitude. Thus, we consider transport-perpendicular lineations like those seen along the Moine thrust zone to be the result of lateral-confining boundary conditions that are weak enough to allow transport-perpendicular maximum extension.

Bone creep can cause progressive vertebral deformity

Introduction Vertebral deformities in elderly people are conventionally termed “fractures”, but their onset is often insidious, suggesting that time-dependent (creep) processes may also be involved. Creep has been studied in small samples of bone, but nothing is known about creep deformity of whole vertebrae, or how it might be influenced by bone mineral density (BMD). We hypothesise that sustained compressive loading can cause progressive and measurable creep deformity in elderly human vertebrae. Methods 27 thoracolumbar “motion segments” (two vertebrae and the intervening disc and ligaments) were dissected from 20 human cadavers aged 42–91 yrs. A constant compressive force of approximately 1.0 kN was applied to each specimen for either 0.5 h or 2 h, while the anterior, middle and posterior heights of each of the 54 vertebral bodies were measured at 1 Hz using a MacReflex 2D optical tracking system. This located 6 reflective markers attached to the lateral cortex of each vertebral body, with resolution better than 10 μm. Experiments were at laboratory temperature, and polythene film was used to minimise water loss. Volumetric BMD was calculated for each vertebral body, using DXA to measure mineral content, and water immersion for volume. Results In the 0.5 h tests, creep deformation in the anterior, middle and posterior vertebral cortex averaged 4331, 1629 and 614 micro-strains respectively, where 10,000 micro-strains represents 1% loss in height. Anterior creep strains exceeded posterior ( P < 0.01) so that anterior wedging of the vertebral bodies increased, by an average 0.08° (STD 0.14°). Similar results were obtained after 2 h, indicating that creep rate slowed considerably with time. Less than 40% of the creep strain was recovered after 2 h. Increases in anterior wedging during the 0.5 h creep test were inversely proportional to BMD, but only in a selected sub-set of 20 specimens with average BMD < 0.15 g/cm 3 ( P = 0.042). Creep deformation caused more than 5% height loss in four vertebrae, three of which had radiographic signs of pre-existing damage. Conclusion Sustained loading can cause progressive anterior wedge deformity in elderly human vertebrae, even in the absence of fracture.

Structure and kinematics of the Indo‐Burmese Wedge: Recent and fast growth of the outer wedge

The northern Sunda subduction zone, offshore Burma, and the associated Indo‐Burmese Wedge mark the active eastern boundary of the Burma Platelet jammed between the India Plate and the Sunda Plate. The aim of this paper is to provide a structural and kinematics analysis of the Indo‐Burmese Wedge based on seismic reflection, geodetic, and geological field data. We found out that the Indo‐Burmese Wedge is the place of diffuse strain partitioning: right‐lateral shearing in the innermost part and E‐W shortening in the outermost part. In the outer wedge, thick‐skinned deformation overprints thin‐skinned deformation. It can be explained by the required preservation of the critical taper after the fast westward propagation of the outer wedge above a very efficient clayey décollement layer. The thick‐skinned deformation is here characterized by major right‐lateral strike‐slip faults (the Kaladan Fault and the Chittagong Coastal Fault) and yet a typical internal deformation of the Indo‐Burmese Wedge. We suggest that the westward migration of internal right‐lateral shear deformation allows preservation of the strain‐partitioning ratios between internal N‐S trending right‐lateral shearing and external E‐W shortening. Some seismic lines show that the outer wedge deformation is not older than 2 Ma. Its propagation could have been enhanced by the large amount of sediments filling up the Sylhet flexural basin formed after the Pliocene tectonic uplift of the Shillong Plateau.

Coseismic strengthening of the shallow portion of the subduction fault and its effects on wedge taper

According to the dynamic Coulomb wedge model, coseismic strengthening of the shallowest part of the subduction interface can cause permanent deformation of the overlying outer wedge, so that the cumulative effects of great interplate earthquakes control the geometry of the wedge. In this work, we use a numerical model, which is a hybrid of the frictional contact model and the classical crack model, to study how stress is coseismically transferred from the seismogenic zone to the strengthening updip zone to cause wedge deformation. In this static model, the “critical strengthening” required to prevent the rupture from breaking the trench depends on the force drop of the seismogenic zone, defined as the product of the average shear stress drop and the area of the seismogenic zone. In a simple model of uniform material properties with a few megapascals average stress drop over a seismogenic zone of 120 km downdip width, the critical strengthening for a 30 km wide updip zone is an increase in the effective friction coefficient by about 0.05. Using the Coulomb wedge theory, we demonstrate that this level of strengthening can readily push the overlying wedge into a critical state of failure. With much greater strengthening, the rupture is able to extend into the updip zone only slightly, causing localized wedge compression in the area of slip termination. We examined wedge geometry of 22 subduction zones in the light of the model results. We found that the surface slope of these wedges is generally too high to be explained using the classical wedge theory but can be explained using the dynamic Coulomb wedge model including coseismic strengthening of the shallow portion of the megathrust.

Tectonic features of the incipient arc-continent collision zone of Taiwan: Implications for seismicity

Southern Taiwan and its offshore area lie in the region where the Luzon volcanic arc initially collides with the rifted China continental margin. Because of the incipient arc-continent collision, the structures vary markedly along-strike the collision zone so as the patterns of seismicity. We use new seismic reflection profiles and integrate existing data to reveal major tectonic features and potential seismogenic faults of the study area. The accretionary wedge in the incipient arc-continent zone can be divided into the lower slope, upper slope, and backthrust domains, respectively. These structural domains reflect different aspects of wedge deformation, and exhibit significant structural variations along-strike. Reflection seismic data show that the prominent seismogenic structures in the Taiwan incipient collisional wedge include: (1) frontal decollement beneath the lower-slope domain, (2) out-of-sequence thrusts bordering the lower-slope and upper-slope domains, (3) megathrust that cuts into the oceanic (?) basement beneath the upper-slope domain, and (4) the Chaochou-Hengchun faults in the onshore upper-slope domain. Thermal regime for those structures indicates that the megathrust and part of frontal decollement are seismogenic. The geometry of the frontal decollement, out-of-sequence thrusts and megathrust is analogous to those observed along the Nankai prism of Japan, so that they are possibly capable of generating great earthquakes as shown in the Nankai Trough. Beneath the lower and upper-slope domains off SW Taiwan, the seismicity is characterized by mantle earthquakes with the accretionary wedge being largely aseismic. We interpret the lack of prominent seismicity within the accreted wedge to result from excess fluid pressure that has significantly weakened the wedge materials and fault zones and therefore results in less seismicity. The predominant mantle earthquakes beneath the accretionary wedge, however, may result from water-enriched mantle materials infiltrated during previous Mesozoic subduction event and later rift events. The volatile contents may have significantly reduced the rigidity of the mantle, leading to the mantle being more susceptible for brittle deformation and hence anomalously high seismicity.

MRI IN THE DIFFERENTIAL DIAGNOSISOF VERTEBRAL WEDGE DEFORMITY

Objective. To specify the MRI abilities in differential diagnosis of vertebral wedge deformity. Material and Methods. The study is based on the analysis of MRI findings in 43 patients aged from 24 to 64 years with a preliminary clinical and radiological diagnosis of pathologic fracture and wedge deformity of vertebral bodies. Results. MRI study revealed vertebral metastases in 31 (72.1 %) patients; inflammatory disease (spondylitis) in 8 (18.6 %), vertebral osteoporosis in 3 (7.0 %), and traumatic vertebral fracture in 1 (2.3 %) patient. Diagnosis in all patients was confirmed by surgical treatment results and clinical examination data. Conclusions. MRI is an informative method for differential diagnosis of the vertebral wedge deformity which provides reliable identification of main pathological processes causing the occurrence of wedge vertebral deformity, decrease in duration of patient’s preliminary examination, and timely choice of the appropriate treatment.

Effect of vertebral wedge deformity on disc degeneration and vertebral slip in patient with spondylolysis

Effect of vertebral wedge deformity on disc degeneration and vertebral slip in patient with spondylolysis

Consequences of continental subduction on forearc basin and accretionary wedge deformation in SE Taiwan: Insights from analogue modeling

In southeastern Taiwan a slice of forearc basement belonging to the Philippine Sea Plate upper-plate is suspected to subduct under the Luzon arc as a consequence of the transition from oceanic to incipient continental subduction. Effects on the morphology, deformation, geometry of structures and tectonic evolution of the orogenic wedge in the collision area are numerous. This study examines the impact of forearc lithosphere subduction on forearc basin and accretionary wedge deformation. A morpho-structural analysis of the geological features observed onland and offshore allows describing in detail the complex deformation suffered by the area. A combined approach by analogue modeling is applied to better understand the phenomenon. Comparison between nature and experimental results shows that subduction of a forearc basement slice induces intense shortening and concomitant deformation in the forearc domain. Such process involves deformation of the forearc basin previously developed in a setting of oceanic subduction. Sediments of the forearc basin are involved in the growth of a new thrust ridge backthrusted against the basement slope of the volcanic arc edifice. Sediments coming from the growing orogenic wedge are trapped in the trough developed between its backpart and the topographic high of the new rising ridge. A syn-collisional orogenic basin develops which structural evolution characterizes the progressive shortening of the forearc domain. Most of the deformation and tectonic events recorded offshore or onland in the complex area south of Taiwan can be explained using results of our specific modeling which well describe the tectonic processes associated with continental subduction under a volcanic arc.

Frontal accretion: An internal clock for bivergent wedge deformation and surface uplift

We propose a conceptual model of frontal accretion within bivergent wedges, which is based on two‐dimensional sandbox simulations and the analysis of particle displacement fields. Each frontal accretion cycle consists of a thrust initiation, an underthrusting phase, and a reactivation phase. The location and magnitude of deformation within a bivergent wedge and its associated surface uplift vary systematically with the phase of the frontal accretion cycle and are thus predictable. Therefore the frontal accretion cycle can be considered as an internal clock for wedge‐scaled deformation and surface uplift. We further demonstrate that the geometry of the deformation front and the spatial distribution of surface uplift can be used to infer the currently active phase within a frontal accretion cycle. Surface uplift of the axial zone and the retrowedge may reach up to half of the thickness of the incoming sedimentary layer during a frontal accretion cycle. We estimate cycle duration to range between 104 and 105 years, which is thus similar to the time frame of climatic cycles. The proposed conceptual model provides an explanation for the commonly observed transience of deformation and surface uplift and for the discrepancy between geodetic, paleoseismologic, and geologic estimates of fault slip.

Stretchable diffraction gratings for spectrometry

We have investigated the possibility of using transparent stretchable diffraction gratings for spectrometric applications. The gratings were fabricated by replication of a triangular-groove master into a transparent viscoelastic. The sample length, and hence the spatial period, can be reversibly changed by mechanical stretching. When used in a monochromator with two slits, the stretchable grating permits scanning the spectral components over the output slit, converting the monochromator into a scanning spectrometer. The spectral resolution of such a spectrometer was found to be limited mainly by the wave-front aberrations due to the grating deformation. A model relating the deformation-induced aberrations in different diffraction orders is presented. In the experiments, a 12-mm long viscoelastic grating with a spatial frequency of 600 line pairs/mm provided a full-width at half-maximum resolution of up to ~1.2 nm in the 580-680 nm spectral range when slowly stretched by a micrometer screw and ~3 nm when repeatedly stretched by a voice coil at 15 Hz. Comparison of aberrations in transmitted and diffracted beams measured by a Shack- Hartmann wave-front sensor showed that astigmatisms caused by stretch-dependent wedge deformation are the main factors limiting the resolution of the viscoelastic-grating-based spectrometer.

Static Versus Dynamic Loading in the Mechanical Modulation of Vertebral Growth

Measures of absolute and relative growth modulation were used to determine the effects of static and dynamic asymmetric loading of vertebrae in the rat tail. To quantify the differences between static and dynamic asymmetric loading in vertebral bone growth modulation. The creation and correction of vertebral wedge deformities have been previously described in a rat-tail model using static loading. The effects of dynamic loading on growth modulation in the spine have not been characterized. A total of 36 immature Sprague-Dawley rats were divided among four different groups: static loading (n = 12, 0.0 Hz), dynamic loading (n = 12, 1.0 Hz), sham operated (n = 6), and growth controls (n = 6). An external fixator was placed across the sixth and eighth caudal vertebrae as the unviolated seventh caudal vertebra was evaluated for growth modulation. Static or dynamic asymmetric loads were applied at a loading magnitude of 55% body weight. After 3 weeks of loading, growth modulation was assessed using radiographic measurements of vertebral wedge angles and vertebral body heights. The dynamically loaded rats had a final average wedge deformity of 15.2+/- 6.4 degrees, which was significantly greater than the statically loaded rats whose final deformity averaged 10.3 degrees +/- 3.7 degrees (P < 0.03). The deformity in both groups was statistically greater than the sham-operated (1.1+/- 2.0 degrees) and growth control rats (0.0+/- 1.0 degrees) (P < 0.001). The longitudinal growth was significantly lower on the concavity compared with the convexity in both the dynamically (0.34 +/- 0.23 mm vs. 0.86 +/- 0.23 mm) and statically (0.46 +/- 0.19 mm vs. 0.83 +/- 0.32 mm) loaded rats (P < 0.001). These growth rates were significantly less than the sham operated and growth control rats (P < 0.001). A variety of fusionless scoliosis implant strategies have been proposed that use both rigid and flexible implants to modulate vertebral bone growth. The results from this study demonstrate that dynamic loading of the vertebrae provides the greatest growth modulation potential.

Mountain building mechanisms in the Southern Central Range of the Taiwan Orogenic Belt — From accretionary wedge deformation to arc–continental collision

Most researches consider the Taiwan Orogeny to be the result of an oblique arc–continental collision between the Philippine Sea Plate and Eurasia Plate. According to kinematic modeling, the mountains started to build from the north and progressively propagated southward at a rate of 60–90 km/my. Because of the oblique nature of the collision, the influence of the collision on mountain building resulted in the southern Central Range experiencing orogenic processes more recently than in the north. In order to test this model, we studied a critical area using zircon and apatite fission-track data to reveal the early exhumation history of the southern Central Range. We find that exhumation started about 6 Ma, which is earlier than the previously predicted timing of mountain building. We also find that the exhumation history can be separated into two stages: an initial stage starting at ca. 6 Ma and continuing to ca. 1 Ma with a slow uplift rate of < 1 mm/yr; and a second stage starting at ca. 1 Ma until the present with a high uplift rate of 4–10 mm/yr. The initial stage of mountain building is considered to be related to accretionary wedge deformation as the South China Sea Plate subducted beneath the Philippine Sea Plate whereas the second stage mountain building resulted from the arc–continental collision. Combining the ages of isotopic dating and fission-track dating in the northern Central Range, we find that the northern Central Range also could start exhumation at ca. 6 Ma and that its exhumation history can also be separated into two stages with similar exhumation patterns and mechanisms to that of the southern Central Range. The most notable difference between the exhumation history of the northern and southern areas of the range is the more extensive degree of exhumation in the north; this could be attributed to the northern Central Range having experienced a longer collision history.

2006 Abstracts: Twenty-Eighth Annual Meeting of the American Society for Bone and Mineral Research: Pennsylvania Convention Convention Center Philadelphia, Pennsylvania, USA, September 15–19, 2006

Vertebral fractures serve as sentinel markers for the epidemiological study of osteoporosis. Using vertebral morphometry from lateral scans of the spine, vertebral fractures were identified in an age-stratified, random sample of 1148 men enrolled in the Geelong Osteoporosis Study (median age 58.5yr, range 20-93). Scans were performed using a Lunar densitometer (Prodigy Pro) for TI 0- 12 and LJ-4. Moderate and severe wedge, biconcave or compression deformities (>25% reduction in any height and accompanying area) were classified as vertebral fractures. Prevalence data were standardised to national age profiles. Osteoporosis and osteopenia were defined using -2.5 SD and -1.0 SD below young normal mean bone mineral density (BMD) values, respectively. Vertebral fractures were identified in 64 men (29 Land 41 T), 47% of whom had selfreported height loss. No fractures were detected for men in their twenties. Agestandardised figures show that men in their thirties have 1.5% prevalence, in their forties 1.4%, fifties 3.2%, sixties 4.7%, seventies 10.0%, and eighties and older 14.6% prevalence. Among men with vertebral fracture, 8% had osteoporosis and 24% osteopenia at the spine, whereas 18% had osteoporosis and 5 I% had osteopenia at the femoral neck. Most (94%) were unaware of their vertebral fracture. Vertebral fracture affects approximately 3% of Australian adult men. Similar to postmenopausal women, a substantial proportion of men with vertebral fracture had mild deficits in BMD and 31% were associated with apparently normal areal BMD at the femoral neck. However, consistent with osteoporosis-related fractures, the prevalence increases with age. Despite nearly half the fracture cases reporting height loss. vertebral fractures are mostly undiagnosed.

Follow-up on Percutaneous Vertebroplasty Using PMMA in Osteoporotic Patients

We reviewed the follow-up findings of patients who received percutaneous vertebroplasty, in order to understand the effects of vertebroplasty on following issues: pain relief, height restoration, wedge deformity correction, kyphosis correction, and other radiological findings found in follow up studies, such as new fractures. Generally, the pain relieving effect after vertebroplasty is long lasting except when new fracture occurred, or presence of other problems that caused the back pain. Height restoration and wedge deformity correction last for more than one year. The effect of kyphosis angle correction may vanish one year after procedure due to occurrence of new fracture in adjacent vertebral bodies.

Mantle wedge deformation by subducting and rotating slab and its possible implication

Abstract We have constructed a simple model of the deformation of the mantle wedge caused by the subducting and rotating slab based on corner flow model. By applying this model to the geological settings of the Somuncura plateau volcanic region, northern Patagonia, which is located far from the volcanic front, we constrain the mechanical aspect of the hypothesis that the volcanisms of the Somuncura region are triggered by the dehydration-induced melting of the up-warped transition zone which may contain more water than other regions do. Assuming that the water concentrates in the transition zone under the Somuncura plateau, we find that the above scenario may be possible, if the speed of the subducting slab is less than ∼2 cm/yr or the dip angle changes significantly (∼50 degrees within ∼8 Myr).