Focal Stress Research Articles

Source mechanisms and faulting analysis of the aftershocks in the Lake Erçek area (Eastern Anatolia, Turkey) during the 2011 Van event (Mw 7.1): Implications for the regional stress field and ongoing deformation processes

In this study, we analysed the source mechanisms and faulting pattern of the aftershocks in the Lake Erçek area, Eastern Anatolia, during the 2011 Van event (Mw 7.1). The fault plane solutions of the aftershocks were used to derive a stress tensor acting around Lake Erçek. The estimated seismological parameters (focal mechanism solutions, stress tensor, and fault focal analyses) were integrated with field surveys and high resolution seismic reflection data so as to better understand the main faulting patterns and deformational features which are the causatives of the observed geomorphological features within and around Lake Erçek. The focal parameters of the 56 aftershocks with magnitude range 3.5≤Mw≤5.5 were obtained using the regional broadband seismic data from the network of Kandilli Observatory and Earthquake Research Institute (KOERI) through the Centroid Moment Tensor (CMT) inversion of locally observed broadband-waves. The implications for the lateral variation of the stress field in the lake area were based on information derived from integration of seismicity and stress tensor inversion results. The major outcomes of our analyses were as follows: (a) The maximum principal stress axis is close to horizontal and aligned in NNW-SSE direction, the minimum compressional stress axis is close to vertical and aligned in an ENE-WSW direction, the intermediate stress axis is close to horizontal and is parallel to the strike of the ruptured fault plane, while the stress ratio is (R=0.6); (b) the lake basin is mostly deformed by dip-slip faults (dips≥45–60°) in and along its margins where the various folds, basement highs with eroded surfaces and several low-angle normal faults are evident; (c) the majority of the aftershocks have reverse-thrust mechanism with some strike-slip components in the Lake Erçek area (N- and S-margins). Strike-slip and normal faulting events are also evident (E- and W-margins, respectively); (d) the normal and reverse mechanisms with some strike-slip component are mostly confined in the upper crust (0–15km), compatible with NS-striking normal and WE-striking reverse faults in the marginal sections of the lake; (e) the WE-striking reverse faulting in the N- and S-margins seems to have the seismic potential to generate destructive earthquakes in the lake area; (f) the tectonic implications of the regional stress field and ongoing deformation processes in the lake are defined and supported by field observations and seismic reflection data. The result of these analyses reveals N-S compression/W-E extension in the lake and also the collisional/compressional regime taking place in a region of Lakes Van and Erçek.

Focal Increased Tc-99m MDP Uptake in the Nutrient Foramen of the Femoral Diaphysis on Bone SPECT/CT.

We present images of an 83-year-old female with a history of osteoporosis and bilateral total knee replacement arthroplasty, referred for bone scintigraphy and single-photon emission computed tomography (SPECT)/computed tomography (CT), owing to left knee pain. No trauma to, or intense exercise of, the knee was reported. The bone scan and SPECT/CT revealed a focally increased Tc-99m methylene diphosphonate (MDP) uptake in the medial cortex of the left femoral diaphysis with matched linear radiolucency on CT images. This was misinterpreted as atypical femoral stress fracture; however, focal stress reaction injury to the nutrient foramen was confirmed on contrast-enhanced magnetic resonance imaging.

Corrigendum: Current crustal deformation of the Taiwan orogen reassessed by cGPS strain-rate estimation and focal mechanism stress inversion

Corrigendum: Current crustal deformation of the Taiwan orogen reassessed by cGPS strain-rate estimation and focal mechanism stress inversion

Blood flow restricted training leads to myocellular macrophage infiltration and upregulation of heat shock proteins, but no apparent muscle damage.

Muscular contractions performed using a combination of low external loads and partial restriction of limb blood flow appear to induce substantial gains in muscle strength and muscle mass. This exercise regime may initially induce muscular stress and damage; however, the effects of a period of blood flow restricted training on these parameters remain largely unknown. The present study shows that short-term, high-frequency, low-load muscle training performed with partial blood flow restriction does not induce significant muscular damage. However, signs of myocellular stress and inflammation that were observed in the early phase of training and after the training intervention, respectively, may be facilitating the previously reported gains in myogenic satellite cell content and muscle hypertrophy. The present results improve our current knowledge about the physiological effects of low-load muscular contractions performed under blood flow restriction and may provide important information of relevance for future therapeutic treatment of muscular atrophy. Previous studies indicate that low-load muscle contractions performed under local blood flow restriction (BFR) may initially induce muscle damage and stress. However, whether these factors are evoked with longitudinal BFR training remains unexplored at the myocellular level. Two distinct study protocols were conducted, covering 3weeks (3wk) or one week (1wk). Subjects performed BFR exercise (100mmHg, 20% 1RM) to concentric failure (BFRE) (3wk/1wk), while controls performed work-matched (LLE) (3wk) or high-load (HLE; 70% 1RM) (1wk) free-flow exercise. Muscle biopsies (3wk) were obtained at baseline (Pre), 8days into the intervention (Mid8), and 3 and 10days after training cessation (Post3, Post10) to examine macrophage (M1/M2) content as well as heat shock protein (HSP27/70) and tenascin-C expression. Blood samples (1wk) were collected before and after (0.1-24h) the first and last training session to examine markers of muscle damage (creatine kinase), oxidative stress (total antibody capacity, glutathione) and inflammation (monocyte chemotactic protein-1, interleukin-6, tumour necrosis factor α). M1-macrophage content increased 108-165% with BFRE and LLE at Post3 (P<0.05), while M2-macrophages increased (163%) with BFRE only (P<0.01). Membrane and intracellular HSP27 expression increased 60-132% at Mid8 with BFRE (P<0.05-0.01). No or only minor changes were observed in circulating markers of muscle damage, oxidative stress and inflammation. The amplitude, timing and localization of the above changes indicate that only limited muscle damage was evoked with BFRE. This study is the first to show that a period of high-frequency, low-load BFR training does not appear to induce general myocellular damage. However, signs of tissue inflammation and focal myocellular membrane stress and/or reorganization were observed that may be involved in the adaptation processes evoked by BFR muscle exercise.

Why location matters - site-specific factors in rheumatic diseases.

Rheumatic diseases follow a characteristic anatomical pattern of joint and organ involvement. This Review explores three interconnected mechanisms that might be involved in the predilection of specific joints for developing specific forms of arthritis: site-specific local cell types that drive disease; systemic triggers that affect local cell types; and site-specific exogenous factors, such as focal mechanical stress, that activate cells locally. The embryonic development of limbs and joints is also relevant to the propensity of certain joints to develop arthritis. Additionally, location-specific homeostasis and disease occurs in skin and blood vessels, thereby extending the concept of site-specificity in human diseases beyond rheumatology. Acknowledging the importance of site-specific parameters increases the complexity of current disease paradigms and brings us closer to understanding why particular disease processes manifest at a particular location.

The 23 January 2014 Jizan earthquake and its tectonic implications in southwestern Saudi Arabia

A moderate-sized earthquake of Mw 4.4 occurred in southwestern Saudi Arabia on 23 January 2014. The event is considered as the largest observed earthquake that has occurred in the epicentral area. To examine the seismogenic stress regime and resolve the fault plane ambiguity, the hypocenter locations and focal mechanisms were determined using well recorded waveforms of the broadband stations operated by the Saudi Geological Survey. The current analysis included dataset consisting of mainshock and a total number of 113 well-located aftershocks. Focal mechanism solutions of the mainshock and fifteen aftershocks were determined. The focal mechanism solutions were inverted using stress tensor inversion. It indicates that the maximum compressive stress, σ1, has a nearly shallow plunge (11.8°) of ESE orientation and minimum compressive stress, σ3, has a shallow plunge (0.3°) toward NNE. Our results obtained from precise earthquake locations, focal mechanism solutions and stress tensor inversion reveal dextral strike-slip faulting over the ENE-WSW striking plane. The analysis of Coulomb failure stress emphasized the causative fault of the 2014 Jizan earthquake sequence. The active fault implies a reactivation of a high-angle fault, buried in the Precambrian basement, which is conjugate to the Red Sea spreading axis and NNW-SSE Najd fault system. The present study provided an impetus toward understanding the seismogenic stress regime in a virgin area.

Tug of War at the Cell-Matrix Interface

Mechanical interactions between a cell and its environment, or between cells, influence key developmental and physiologic processes as well as many aspect of disease (1,2). Indeed the ability of a cell to sense, produce, and respond to mechanical cues has emerged as a fundamental regulator of cell behaviors such as differentiation, proliferation, survival, and migration. In mechanical terms the interactions governing these behaviors are regulated by intracellular and extracellular physical events that are orchestrated by complex biochemical and mechanical signals.

Current crustal deformation of the Taiwan orogen reassessed by cGPS strain-rate estimation and focal mechanism stress inversion

Current crustal deformation of the Taiwan orogen reassessed by cGPS strain-rate estimation and focal mechanism stress inversion

Effect of Stitching on the Tensile Mechanical Property of Empty Fruit Bunch Oil Palm Fiber Reinforced Epoxy Composites

Stitching has proven to be an effective reinforcement for improving through-thickness (out-of-plane) mechanical properties with the incorporation of z-direction reinforcements of synthestic fiber. There are drawbacks to stitching as it may cause focal stress concentration, and fiber misalignment and breakage, but at the same time, it can also improve the tensile performance of the composite. Tensile properties, such as tensile strength and modulus of elasticity, were obtained from tensile tests performed on both stitched and unstitched oil palm fiber composites as per ASTM D638 specifications using Universal Testing Machine INSTRON 5582. The test results indicated that stitching natural, short, untreated and random empty fruit bunch oil palm fiber reinforced epoxy composites improve the tensile strength and elastic modulus due to the increase in matrix volume percentage and additional tensional resistance.

Biomechanical comparison of two ostectomy configurations for partial mandibulectomy.

To determine the stiffness and load to failure of two different ostectomy configurations using canine mandibles. Cadaveric biomechanical assessment. Paired mandibles (n = 30). Standardized partial ostectomies were created on the alveolar surface of 30 mandibles. Samples were randomly assigned to right-angled (n = 15) or crescentic ostectomy (n = 15). Excision spanned the mesial aspect of the fourth premolar tooth to the distal aspect of first molar tooth. Mandibles were loaded to failure in three-point bending. The stiffness, displacement at maximum load, and load to failure were measured. There was no significant difference in stiffness (p = 0.59), displacement at maximum load (p = 0.16) and load to failure (p = 0.76) between right-angled or crescentic ostectomy. Right-angled and crescentic ostectomy failed mostly by fracture through an empty alveolus (11/15 and 13/15, respectively). No significant differences in load to failure or stiffness between ostectomy techniques were observed. Crescentic ostectomy did not improve the acute load to failure for partial mandibulectomy. The empty alveolus served as a focal stress concentration point eliminating the potential mechanical advantage of a crescentic ostectomy.

Do they understand more? Turkish EFL speakers perception of sentence stress in English

As one of the most prominent elements of intonation sentence stress frequently contributes to the meaning expressed by speakers. It most typically signals details of an utterance information structure, but it also performs a contrastive or emphasizing function, thus expressing focus in the spoken discourse. In English and many other languages its location, while exhibiting certain regularities it additionally determined by extra relevant or relative information. As such, either alone or in combination, it may communicate certain additional shades of meaning that, similarly to the contribution of sentence intonation, may escape the attention of EFL speakers.&#x0D; The paper explores the comprehension sensitivity of Turkish speakers of English when it comes to identifying meaning details contributed by sentence stress. It investigates their awareness as detected through perception of variable sentence stress location. The target group are Turkish advanced speakers of English, with various levels of competence, and only sporadic phonetic training in English for part of them. In a perception-based experiment they were asked to identify the details they perceive. Their results were then compared and analysed, also in relation to what their native language (with a distinction into sentential and focal stress) adds in terms of this module of utterance intonation. Finally, their results were correlated with those achieved by Polish advanced speakers of English as investigated in a similar study conducted earlier. The interpretation of the results reveals that Turkish EFL speakers are more sensitive to the highlighting or contrastive function of sentence stress, achieving overall better result here than when they are to judge its contribution to notion such as politeness or impatience. They are also rather competent at detecting the prominent element in an utterance.

Focal mechanisms and stress variations in the Caucasus and Northeast Turkey from constraints of regional waveforms

The continental collision between Arabia and Eurasia created large strike-slip faults in Turkey as well as mountains in the Caucasus and the volcanic plateau between them. In this study, we use regional waveforms of a new seismic array deployed between 2008 and 2012 to constrain the focal mechanisms and depths of small to moderate sized earthquakes occurring in the western part of the Central Caucasus and northeast Turkey. The distribution of aftershocks and the twelve focal mechanisms involved in the sequence of the 2009 earthquake in Racha are clearly a reactivation of a deeper segment of the 1991 M7 Racha rupture zone. The deeper segment is not well connected to the shallower décollement separating the basement and sedimentary basin. The earthquakes we determined in northeastern Turkey and southern Georgia are related to the strike-slip fault system. We further combined all of the reliably determined focal mechanisms over the last 30years to investigate the current stress status of the crust in three areas: Racha in the western Greater Caucasus, Javakheti near the Lesser Caucasus and in Northeast Turkey. Our results show that the directions of maximum compressional stress consistently fall within −2 to 14°N throughout the entire study region. This appears to be controlled by the continental collision. Nonetheless, the minimum compression switches from vertical (in the Greater Caucasus) to the east-west direction (in northeastern Turkey), due to the westward extrusion of the Anatolia block, which is driven partly by the Hellenic subduction. The transition of the stress field is close to the Javakheti volcanic plateau in the Lesser Caucasus, where the relative magnitude between the principal stresses appears to be strongly variable.

Impact of fluid injection on fracture reactivation at The Geysers geothermal field

AbstractWe analyze the spatiotemporal distribution of fault geometries from seismicity induced by fluid injection at The Geysers geothermal field. The consistency of these faults with the local stress field is investigated using (1) the fault instability coefficient I comparing the orientation of a fault with the optimal orientation for failure in the assumed stress field and (2) the misfit angle β between slip vectors observed from focal mechanisms and predicted from stress tensor. A statistical approach is applied to calculate the most likely fault instabilities considering the uncertainties from focal mechanisms and stress inversion. We find that faults activated by fluid injection may display a broad range in orientations. About 72% of the analyzed seismicity occurs on faults with favorable orientation for failure with respect to the stress field. However, a number of events are observed either to occur on severely misoriented faults or to slip in a different orientation than predicted from stress field. These events mostly occur during periods of high injection rates and are located in proximity to the injection wells. From the stress inversion, the friction coefficient providing the largest overall instability is μ = 0.5. About 91% of the events are activated with an estimated excess pore pressure &lt;10 MPa, in agreement with previous models considering the combined effect of thermal and poroelastic stress changes from fluid injection. Furthermore, high seismic activity and largest magnitudes occur on favorably oriented faults with large instability coefficients and low slip misfit angles.

Dynamin Autonomously Regulates Podocyte Focal Adhesion Maturation

Rho family GTPases, the prototypical members of which are Cdc42, Rac1, and RhoA, are molecular switches best known for regulating the actin cytoskeleton. In addition to the canonical small GTPases, the large GTPase dynamin has been implicated in regulating the actin cytoskeleton via direct dynamin-actin interactions. The physiologic role of dynamin in regulating the actin cytoskeleton has been linked to the maintenance of the kidney filtration barrier. Additionally, the small molecule Bis-T-23, which promotes actin-dependent dynamin oligomerization and thus, increases actin polymerization, improved renal health in diverse models of CKD, implicating dynamin as a potential therapeutic target for the treatment of CKD. Here, we show that treating cultured mouse podocytes with Bis-T-23 promoted stress fiber formation and focal adhesion maturation in a dynamin-dependent manner. Furthermore, Bis-T-23 induced the formation of focal adhesions and stress fibers in cells in which the RhoA signaling pathway was downregulated by multiple experimental approaches. Our study suggests that dynamin regulates focal adhesion maturation by a mechanism parallel to and synergistic with the RhoA signaling pathway. Identification of dynamin as one of the essential and autonomous regulators of focal adhesion maturation suggests a molecular mechanism that underlies the beneficial effect of Bis-T-23 on podocyte physiology.

Structure and calcium-binding studies of calmodulin-like domain of human non-muscle α-actinin-1

The activity of several cytosolic proteins critically depends on the concentration of calcium ions. One important intracellular calcium-sensing protein is α-actinin-1, the major actin crosslinking protein in focal adhesions and stress fibers. The actin crosslinking activity of α-actinin-1 has been proposed to be negatively regulated by calcium, but the underlying molecular mechanisms are poorly understood. To address this, we determined the first high-resolution NMR structure of its functional calmodulin-like domain (CaMD) in calcium-bound and calcium-free form. These structures reveal that in the absence of calcium, CaMD displays a conformationally flexible ensemble that undergoes a structural change upon calcium binding, leading to limited rotation of the N- and C-terminal lobes around the connecting linker and consequent stabilization of the calcium-loaded structure. Mutagenesis experiments, coupled with mass-spectrometry and isothermal calorimetry data designed to validate the calcium binding stoichiometry and binding site, showed that human non-muscle α-actinin-1 binds a single calcium ion within the N-terminal lobe. Finally, based on our structural data and analogy with other α-actinins, we provide a structural model of regulation of the actin crosslinking activity of α-actinin-1 where calcium induced structural stabilisation causes fastening of the juxtaposed actin binding domain, leading to impaired capacity to crosslink actin.

Number of pegs influence focal stress distributions and micromotion in glenoid implants: a finite element study.

The present study was conducted to compare the stability of four commercially available implants by investigating the focal stress distributions and relative micromotion using finite element analysis. Variations in the numbers of pegs between the implant designs were tested. A load of 750N was applied at three different glenoid positions (SA: superior-anterior; SP: superior-posterior; C: central) to mimic off-center and central loadings during activities of daily living. Focal stress distributions and relative micromotion were measured using Marc Mentat software. The results demonstrated that by increasing the number of pegs from two to five, the total focal stress volumes exceeding 5MPa, reflecting the stress critical volume (SCV) as the threshold for occurrence of cement microfractures, decreased from 8.41 to 5.21% in the SA position and from 9.59 to 6.69% in the SP position. However, in the C position, this change in peg number increased the SCV from 1.37 to 5.86%. Meanwhile, micromotion appeared to remain within 19-25µm irrespective of the number of pegs used. In conclusion, four-peg glenoid implants provide the best configuration because they had lower SCV values compared with lesser-peg implants, preserved more bone stock, and reduced PMMA cement usage compared with five-peg implants.

Phosphatidylinositol 3-Kinase and Protein Kinase C Signaling Pathways Are Involved in Stromal Cell–derived Factor-1α–mediated Transmigration of Stem Cells from Apical Papilla

IntroductionPreviously, we have shown that stem cells from apical papilla (SCAPs) can be chemoattracted by stromal cell–derived factor-1α (SDF-1α). The purpose of this study was to investigate the intracellular signaling pathways involved in SDF-1α–mediated migration of SCAPs. MethodsChemotaxis assays were performed to assess the effect of phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) signaling pathways in the SDF-1α–mediated migration of SCAPs using inhibitors of PI3K (LY294002) or PKC (GF109203X). The Cell Counting Kit-8 assay (Dojindo Laboratories, Kumamoto, Japan) was used to evaluate the effect of the inhibitors on the proliferation of SCAPs. The expression of focal adhesion–related proteins was examined by immunofluorescence staining and Western blot analysis. Phosphorylation of PI3K subunit p85 and PKC after SDF-1α induction was evaluated by Western blot. ResultsThe inhibition of PI3K or PKC signaling pathways significantly reduced SDF-1α–mediated migration of SCAPs. The inhibitors had no effect on the proliferation of SCAPs. Immunofluorescence analysis revealed that SDF-1α stimulated focal adhesion formation and stress fiber assembly in SCAPs, in addition to up-regulation of the expression of focal adhesion molecules, including p-focal adhesion kinase, p-paxillin, and vinculin. Pretreatment with PI3K or PKC inhibitors before SDF-1α induction significantly inhibited focal adhesion molecule expression. Moreover, increased phosphorylation of p85 and PKC were observed after SDF-1α stimulation, whereas these phosphorylations were down-regulated by the inhibition of PI3K or PKC signaling pathways. ConclusionsPI3K and PKC signaling pathways appear to be required for SDF-1α–mediated transmigration of SCAPs. These findings provide insights into the signaling mechanisms that underlie SDF-1α–mediated migration of SCAPs.

Superior Rim Stability of the Lens Capsule Following Manual Over Femtosecond Laser Capsulotomy.

Cataract surgery requires the removal of a circular segment of the anterior lens capsule (LC) by manual or femtosecond laser (FL) capsulotomy. Tears in the remaining anterior LC may compromise surgical outcome. We investigated whether biophysical differences in the rim properties of the LC remaining in the patient after manual or FL capsulotomy (FLC) lead to different risks with regard to anterior tear formation. Lens capsule samples obtained by either continuous curvilinear capsulorhexis (CCC) or FLC were investigated by light microscopy, laser scanning confocal microscopy, and scanning electron microscopy; atomic force microscopy (AFM) was used to test the biomechanical properties of the LC. The mechanical stability of the LC following either of the two capsulotomy techniques was simulated by using finite-element modeling. Continuous curvilinear capsulorhexis produced wedge-shaped, uniform rims, while FLC resulted in nearly perpendicular, frayed rims with numerous notches. The LC is composed of two sublayers: a stiff epithelial layer that is abundant with laminin and a softer anterior chamber layer that is predominantly made from collagen IV. Computer models show that stress is uniformly distributed over the entire rim after CCC, while focal high stress concentrations are observed in the frayed profiles of LC after FLC, making the latter procedure more prone to anterior tear formation. Finite-element modeling based on three-dimensional AFM maps indicated that CCC leads to a capsulotomy rim with higher stress resistance, leading to a lower propensity for anterior radial tears than FLC.

The shape of the hip joint as a risk factor for osteoarthritis

Purpose: Cam-type femoroacetabular impingement characterized by extra bone formation at the anterolateral head-neck junction of the hip creates a non-spherical femoral head, known as a cam deformity. The cam deformity is forced into the acetabulum during flexion and internal rotation of the hip, leading to structural damage as acetabular labrum tears and cartilage delamination. This damage might gradually lead to osteoarthritis. Cam deformity and subtle acetabular dysplasia are recently recognized as relevant risk factors for hip osteoarthritis (HOA). In subtle acetabular dysplasia, the femoral head has contact with a small area of the shallowacetabulum. Therefore, more focal stress is put on this small area, which provides insufficient coverage for the femur. Cumulative articular surface contact stress above a critical threshold in dysplastic joints causes joint degeneration. However, the influence of these deformities on HOA incidence compared with other risk factors including age, gender, and body mass index (BMI) and the effect modification of other known determinants on these associations are not yet known. Methods: Participants of Rotterdam Study (RS-I: n = 2960, RS-II: n = 1470) including men and women aged >55 years with a Kellgren and Lawrence (K/L) grade ≥1 at baseline and mean follow-up of 9.2 years were included in the study. Incident radiographic HOA was defined as a K/L grade of ≥2 or a total joint replacement at follow-up. The shape of the proximal femur and the acetabulumwere outlined by a set of points (23 points, Figure 1) that were positioned on pre-defined anatomical landmarks on the anteroposterior pelvic radiographs using statistical shape modeling software. Using this point set, alpha and center-edge (CE) angles, parameters that quantify these deformities were calculated. Acetabular dysplasia and cam deformity were defined as the presence of a CE angle 60°, respectively (Figure 1). Using generalized estimating equation models, odds ratios were calculated to assess the associations between both hip deformities and the development of HOA. Results: At the follow-up times, 234 and 179 cases of HOAwere identified for RS-I and RS-II, respectively. Incident OA was defined in 281 hips within RS-I among that 12.2% (n = 34) had cam deformity and 8.3% (n = 23) had acetabular dysplasia, while out of 218 hips with incident OA in RS-II,16.1% (n = 35) had cam deformity and 7.3% (n = 16) had dysplasia. In pooled data analyses (Table 1), individuals with cam deformity had a two-fold increased risk for developing osteoarthritis (OR = 2.0, 95% CI= 1.48-2.71, p = 0.00001) compared with individuals without cam deformity. Moreover, subtle acetabular dysplasia was significantly associated with increased risk of HOA (OR = 1.96, 95% CI = 1.35-2.84, p = 0.0004). Both associations were independent of known risk factors of HOA such as age, sex, and BMI and were only significantly associated with development of OA in younger individuals. These bony deformities were independently related to the outcomewhen included in the samemodel (camdeformity: OR (95% CI) = 2.03 (1.50-2.76), hip dysplasia: OR (95% CI) = 2.03 (1.41-2.92)). The results were almost consistent in both cohorts. Conclusions: Individuals with cam deformity and acetabular dysplasia are strongly predisposed to progression to HOA independently from other well known risk factors of age, sex, and BMI. Interestingly, both deformities were only predisposing to OA in relatively young individuals. Therefore, early identification of these conditions is important and might provide an opportunity to prevent hip osteoarthritis. (Figure Presented).

Seismicity and state of stress in the central and southern Peruvian flat slab

Abstract We have determined the Wadati–Benioff Zone seismicity and state of stress of the subducting Nazca slab beneath central and southern Peru using data from three recently deployed local seismic networks. Our relocated hypocenters are consistent with a flat slab geometry that is shallowest near the Nazca Ridge, and changes from steep to normal without tearing to the south. These locations also indicate numerous abrupt along-strike changes in seismicity, most notably an absence of seismicity along the projected location of subducting Nazca Ridge. This stands in stark contrast to the very high seismicity observed along the Juan Fernandez ridge beneath central Chile where, a similar flat slab geometry is observed. We interpret this as indicative of an absence of water in the mantle beneath the overthickened crust of the Nazca Ridge. This may provide important new constraints on the conditions required to produce intermediate depth seismicity. Our focal mechanisms and stress tensor inversions indicate dominantly down-dip extension, consistent with slab pull, with minor variations that are likely due to the variable slab geometry and stress from adjacent regions. We observe significantly greater variability in the P-axis orientations and maximum compressive stress directions. The along strike change in the orientation of maximum compressive stress is likely related to slab bending and unbending south of the Nazca Ridge.