Relationship between fracture spacing and bed thickness in sedimentary rocks: Approach by means of Michaelis–Menten equation

RÉSUMÉ: Fractures occur in nearly all rocks at the Earth's surface and exert essential control on the mechanical strengths of rock masses and permeability. The fractures strongly impact the stability of geological or man-made structures and flow of water and hydrocarbons, CO2 and storing waste. For this, the dependence of opening mode fracture spacing (s) on bed thickness (t) in sedimentary basins (reservoirs) is studied in this context. This paper shows that the Michaelis–Menten equation can provide an algebraic expression for the nonlinear s-t relationship. The two parameters have clear geological meanings: a is the maximum fracture spacing which can no longer increase with increasing t, and b is the characteristic bed thickness when s = 0.5a. The tensile fracture strength (C) of the brittle beds during the formation of tensile fractures can be estimated from the two parameters. For sandstones of 16 areas reported in the literature, C ranges from 2.7 MPa to 15.7 MPa with a mean value of 8 MPa, which lies reasonably within the range of tensile strengths determined experimentally. This field-based approach by means of Michaelis–Menten equation provides a new method for estimating the tensile fracture strength of rock layers under natural conditions

Effects of porosity on seismic velocities, elastic moduli and Poisson's ratios of solid materials and rocks

The generalized mixture rule (GMR) is used to provide a unified framework for describing Young's (E), shear (G) and bulk (K) moduli, Lame parameter (λ), and P- and S-wave velocities (Vp and Vs) as a function of porosity in various isotropic materials such as metals, ceramics and rocks. The characteristic J values of the GMR for E, G, K and λ of each material are systematically different and display consistent correlations with the Poisson's ratio of the nonporous material (ν0). For the materials dominated by corner-shaped pores, the fixed point at which the effective Poisson's ratio (ν) remains constant is at ν0 = 0.2, and J(G) > J(E) > J(K) > J(λ) and J(G) 0.2 and ν0 J(Vp) and J(Vs) 0.2 and ν0 0.2 and ν0 = 0.2, respectively. For natural rocks containing thin-disk-shaped pores parallel to mineral cleavages, grain boundaries and foliation, however, the ν fixed point decreases nonlinearly with decreasing pore aspect ratio (α: width/length). With increasing depth or pressure, cracks with smaller α values are progressively closed, making the ν fixed point rise and finally reach to the point at ν0 = 0.2

The formation of orthogonal joint systems and cuboidal blocks: New insights gained from flat-lying limestone beds in the region of Havre-Saint-Pierre (Quebec, Canada)

ABSTRACT: Vertical orthogonal joints are a common feature in shallow crustal rocks. There are several competing theories for their formation despite the ubiquity. We examined the exceptional exposures of orthogonal joints in flat-lying Ordovician limestone beds from the Havre-Saint-Pierre Region in Quebec, Canada (north shore of Saint-Lawrence River) to test conceptual models of joint formation in a natural setting. In the region, the spacing of cross-joints is consistently larger than the spacing of systematic joints by a factor of 1.5 approximately. The joint-spacing-to-bed-thickness ratios (s/t) are much larger in these beds (s/t = 4.3 for systematic joints, and 6.4 for cross-joints) than those in higher strained strata along the south shore of the Saint-Lawrence River (s/t = 1), highlighting the effect of tectonic strain in decreasing fracture spacing and block size. The high values of s/t indicate that cross-joint formation was unlikely caused by a switch from compression to tension once a critical s/t ratio for systematic joints was reached (as hypothesized in previous studies). We proposed a new model for the formation of orthogonal joint systems where the principal stress axes locally switch during the formation of systematic fractures. The presence of ladder-shaped orthogonal joints suggests a state of effective stress with σ1∗»0 > σ2∗>σ3∗ and where σ2∗-σ3∗ is within the range of fracture strength variability at the time of fracture. This research provides a new mechanical model for the formation of orthogonal joint systems and cuboidal blocks

Uplift of the Longmen Shan range and the Wenchuan earthquake

ABSTRACT: The 12 May 2008 Wenchuan earthquake (M-s,=8.0) struck on the Longmen Shan foreland thrust zone. The event took place within the context of long-term uplift of the Longmen Shan range is a result of the extensive eastward-extrusion of crustal materials from the Tibetan plateau against the rheologically strong crust of the Sichuan Basin. The Longmen Shan range is characterized by a Pre-Sinian crystalline complex constrained by the Maoxian-Wenchuan-Kangding ductile detachment at the western margin and the Yingxiu-Beichuan-Luding ductile thrust at the eastern margin. The Longmen Shan uplift was initiated by intracontinental subduction between the Songpan-Ganzi terrane and the Yangtze block during the Pre-Cenozoic. The uplift rate was increased considerably by the collision between the Indian and Eurasian plates since similar to 50 Ma. The Wenchuan earthquake resulted in two major NE-striking coseismic ruptures (i.e., the similar to 275 km long Yingxiu-Beichuan-Qingchuan fault and the similar to 100 km long Anxian-Guanxian fault). Field investigations combined with focal solutions and seismic reflection profiles suggest that the coseismic ruptures are steeply dipping close-to-pure reverse or right reverse oblique slip faults in the similar to 15 km thick tipper crust. These faults are unfavorably oriented for frictional slip in the horizontally compressional regime, so that they need a long recurrence interval to accumulate the tectonic stress and fluid pressure to critically high levels for the formation of strong earthquakes at a given locality. It is also found that all the large earthquakes (M-s>7.0) occurred in the fault zones across which the horizontal movement velocities measured by the GPS are markedly low (<3 mm/yr). The faults, which constitute the northeastern fronts of the enlarging Tibetan plateau against the strong Sichuan Basin, Ala Shan and Ordos blocks, are very destructive, although their average recurrence intervals are generally long

Integrating MicroRNA Expression Profiling Studies to Systematically Evaluate the Diagnostic Value of MicroRNAs in Pancreatic Cancer and Validate Their Prognostic Significance with the Cancer Genome Atlas Data

Background/Aims: MicroRNAs (miRNAs) are promising biomarkers for pancreatic cancer (PaCa). However, systemic and unified evaluations of the diagnostic value of miRNAs are lacking. Therefore, we performed a systematic evaluation based on miRNA expression profiling studies. Methods: We obtained miRNA expression profiling studies from Gene Expression Omnibus (GEO) and ArrayExpress (AE) databases and calculated the pooled sensitivity, specificity, and summary area under a receiver operating characteristic (ROC) curve for every miRNA. According to the area under the curve (AUC), we identified the miRNAs with diagnostic potentiality and validated their prognostic role in The Cancer Genome Atlas (TCGA) data. Gene Ontology (GO) annotations and pathway enrichments of the target genes of the miRNAs were evaluated using bioinformatics tools. Results: Ten miRNA expression profiling studies including 958 patients were used in this diagnostic meta-analysis. A total of 693 miRNAs were measured in more than 9 studies. The top 50 miRNAs with high predictive values for PaCa were identified. Among them, miR-130b had the best predictive value for PaCa (pooled sensitivity: 0.73 [95% confidence intervals (CI) 0.44-0.91], specificity: 0.81 [95% CI 0.59–0.93], and AUC: 0.84 [95% CI 0.73–0.95]). We identified nine miRNAs (miR-23a, miR-30a, miR-125a, miR-129-1, miR-181b-1, miR-203, miR-221, miR-222, and miR-1301) associated with overall survival in PaCa patients by combining our results with TCGA data. The results of a Cox model revealed that two miRNAs (miR-30a [hazard ratio (HR)=2.43, 95% CI 1.05-5.59; p=0.037] and miR-203 [HR=3.14, 95% CI 1.28-7.71; p=0.012]) were independent risk factors for prognosis in PaCa patients. In total, 405 target genes of the nine miRNAs were enriched with Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and cancer-associated pathways such as Ras signaling pathways, phospholipase D signaling pathway, and AMP-activated protein kinase (AMPK) signaling pathway were revealed among the top 20 enriched pathways. There were significant negative correlations between miR-181b-1 and miR-125a expression levels and the methylation status of their promoter region. Conclusion: Our study performed a systematic evaluation of the diagnostic value of miRNAs based on miRNA expression profiling studies. We identified that miR-23a, miR-30a, miR-125a, miR-129-1, miR-181b-1, miR-203, miR-221, miR-222, and miR-1301 had moderate diagnostic value for PaCa and predicted overall survival in PaCa patients

Development of New Lagrangian Computational Methods for Ice-Ship Interaction Problems: NICESHIP Project

This document presents the activities carried out to date (04/2019) in the project &lsquo;Development of new Lagrangian computational methods for ice-ship interaction problems&rsquo; (NICE-SHIP). The NICE-SHIP project aims at developing a new generation of computational methods, based on the integration of innovative Lagrangian particle-based and finite element procedures for the analysis of the operation of a vessel in an iced sea, taking into account the different possible conditions of the ice. It is expected that the computational analysis techniques to be developed in NICE-SHIP will allow ice-class vessel designers to accurately evaluate the loads acting on the structure of a ship navigating in iced-seas and, in particular, to determine the ice resistance of the ship in different ice conditions