Stress Regime Research Articles

Representative rupture stress-based parameter for characterizing the intensity of creep fracture constraint effect on creep crack growth rate

The introduction of creep fracture constraint parameter offers the possibility of accurately obtaining the CCG rate for specimens/structures subject to different constraint levels through the establishment of constraint-dependent CCG rate equation. However, experimental evidence indicates that the existing constraint-dependent CCG rate equation is generally material- and stress regime-dependent. It is noted that the dependencies may be attributed to the intrinsic difference in creep failure mechanisms of materials, which has not been fully considered by previous constraint parameters. To cope with the dependencies, a parameter, Kz, for characterizing the intensity of constraint effect is proposed in this work based on the representative rupture stress, which could better reflect the operative creep failure mechanism sustained by the material. To justify the parameter, finite element analysis is carried out for five different materials based on experimental data available in the literature. Results show that, compared to the existing constraint parameters, R* and Ac, the Kz is capable of characterizing the crack-tip constraint level under the influence of creep failure mechanism. Furthermore, a generalized constraint-dependent CCG rate equation is established based on the Kz, which overcomes the material and stress regime dependencies of the existing equation. Finally, to clarify the advantage of the Kz, further comparison between the new parameter and the existing parameters is made.

Building a carbon dioxide storage portfolio for the Barrow-Dampier sub-basins through regional screening – an integrated geoscience approach

Safe geological carbon dioxide (CO2) storage (GCS) requires rocks with suitable injectivity, capacity and sealing properties to ensure secure long-term containment of injected CO2. A regional understanding of the subsurface is essential to determine the potential for GCS of a basin and to select target sites. This is best addressed by integrating the basin’s tectono-stratigraphic evolution, its gross depositional environment, and its hydrodynamic, thermal and stress regimes. A basin-scale GCS assessment for the Barrow-Dampier sub-basins was conducted by Geoscience Australia and SLB. The objective of the study is to high-grade geological intervals and sites for potential GCS and to understand potential storage capacity and key risk factors. Stratigraphic and structural mapping of key storage intervals was performed using the reprocessed seismic volume and well database associated with the project. Analysis of critically stressed faults was used to estimate the likelihood of reactivation based on the far-field regional stress field and fault mechanical properties. Pressure, temperature, porosity, permeability, and water geochemistry data have been screened for >500 wells for assessing the storage unit intervals and predicting the hydrodynamic regime. Calibrated 2D basin models provide information on the regional pressure-temperature regime, porosity/permeability distribution, and sealing effectiveness. Potentiometric surface maps for the aquifer systems inform the distribution of potential CO2 plume migration. Results of this integrated regional basin study are used to quantify the risk of identified storage containers and to map the chance of success for GCS at a regional scale. The project results are publicly available via NOPIMS.

Structural framework of the Caswell Sub-basin, North West Shelf, Australia

The Caswell Sub-basin, situated within the Browse Basin in the North West Shelf constitutes one of Australia’s primary hydrocarbon producing regions, with notable gas-condensate producing fields including Ichthys and Prelude. Jurassic syn-rift sandstones are extensively distributed across the basin and serve as one of the major reservoirs. However, reservoir sequences are typically intensely faulted and exhibit heterogeneity in thickness and lithofacies, with some areas experiencing localised erosion on uplifted fault blocks (e.g. Northern Caswell Sub-basin). Hence, understanding the nature of the 3D fault patterns and their growth history is crucial for evaluating the reservoir characteristics for field development and additional exploration activities. This study, therefore, aims to evaluate the structural framework and the tectonic evolution of the Caswell Sub-basin. Detailed structural interpretation of Paleozoic and younger sequences was conducted using multiple 3D seismic datasets extending over Ichthys, Prelude, Lasseter, and Crown fields. Our study focuses mainly on Mesozoic faulting patterns and kinematics evaluated from interpreted structural maps, thickness changes of each stratigraphic interval and fault throw profiles of major bounding faults. The extensional phase during the Early–Middle Jurassic triggered the development of NE–SW trending faults and the deepening of the Brewster Graben. While, from the Late Jurassic to the Early Cretaceous, the development of E–W trending faults in the north of the Crown and Lasseter fields indicate a shift in the regional stress regime. We highlight the importance of evaluating the structural linkage from basement to cover sequences to achieve a comprehensive understanding of reservoirs and associated petroleum systems.

Variation of vertical stress in the McArthur and Beetaloo basins

The McArthur and Beetaloo basins have been the focus of unconventional hydrocarbon exploration, specifically targeting shale gas and tight gas resources. Vertical stress (SV), which is one of the three principal stresses, is a critical parameter in geomechanical analysis of sedimentary basins and has implications in fracture gradient calculation, pore pressure prediction, assessing the present-day stress regime, and hydraulic fracturing design. In addition, variations in vertical stresses can yield additional insights into the tectonic history of an area. In this study, we examine the variability of vertical stress magnitude and vertical stress gradients by employing a systematic analysis of density log and check-shot velocity data obtained from 31 wells located within the McArthur and Beetaloo basins. Our analysis revealed that vertical stress gradients range from 23 to 27 MPa/km (equivalent to ~1.0–1.2 psi/ft), with an average gradient of 25 MPa/km ± 1.0 (1.1 psi/ft). This variability in SV gradients underscores the inadequacy of the commonly assumed 1.0 psi/ft approximation for geomechanical analyses within these basins. The origins of such diverse SV gradients can be attributed to several factors; however, the likely cause of the SV gradient within this region is the presence, thickness, and depth of the shallow high-density volcanic rocks and a complex history of uplift and erosion.

Image analysis of acoustic data and interpretation of rock stress orientations for geothermal exploration in Gothenburg borehole GE-1, SW Sweden

Abstract This study contributes to geothermal exploration in 1660–1520 Ma old, reworked bedrock in Sweden. Our primary objectives are to constrain the orientation of horizontal stresses, and to discuss implications for geothermal exploration. High-resolution acoustic televiewer image data reveal the downhole distribution of stress indicators (borehole breakouts, drilling-induced fractures and petal centreline fractures) and pre-existing structures (natural fractures, foliation). About 135 m of stress indicators are measured from 0.2–1.0 km. The results suggest a uniform NNW–SSE mean maximum horizontal stress orientation. A total of 1525 pre-existing structures (natural fractures, foliation) are mapped in borehole GE-1. The prevailing stress regime controls whether natural fractures and foliation are well-oriented for stimulation. For strike-slip and normal faulting stress regimes, well-oriented fractures steeply dip towards the WSW. For a reverse faulting stress regime, shallow dipping fractures are well-oriented for stimulation. The downhole distribution of stress indicators and other stress measurements in the region and other parts of Fennoscandia tentatively suggest a strike-slip stress regime, but additional studies are needed to constrain the complete stress field at study depth and towards engineered geothermal systems reservoir target depths. Our secondary objective is to highlight that interpretation of high-resolution acoustic data, particularly in metamorphic crystalline rocks, is subjective and that more guidelines for data interpretation are needed. The interactive interpretation of the images is based on visual analyses of complex pre-existing structures and stress indicators with highly variable shapes. The application of three methods for data analyses in the GE-1 borehole proposes that drilling-induced fractures are little influenced by the method applied. Interpretations on individual borehole breakout azimuths may, however, result in over 10° differences in orientation.

2730–2670 Ma rifting triggers sagduction prior to the onset of orogenesis at ca 2650 Ma: implications for gold mineralisation, Eastern Goldfields, Western Australia

The dominant structural fabric in the Eastern Goldfields is the steep north- to north-northwest-trending S2 foliation that is axial planar to upright F2 folds, developed during intense horizontal east–west shortening (D2–4 event). These structures consistently overprint D1 structures, which comprise layer-parallel S1 foliation, extensional shears, thrusts and recumbent F1 folds. The D1 event represents a separate and distinct episode of deformation with a markedly different stress regime (dominant vertical σ1), compared with the stress regime during the D2–4 events (horizontal east–west oriented σ1). There is little evidence for pre-2670 Ma ductile deformation in the Eastern Goldfields, as: (1) the ca 2730–2670 Ma greenstone sequences are deposited conformably on the older ca 2800 Ma greenstone sequences, with the first significant angular unconformities observed at the base of the post greenstone late basins; (2) a lack of schist or gneiss clasts in the late basins suggests that the surrounding uplifted sequence was largely undeformed; (3) the layer-parallel S1 foliation is observed throughout the 2720–2670 Ma greenstone sequence; and (4) the dominant low north- and south-plunges of F2 folds suggest that the sequence was predominantly flat-lying prior to strong east–west shortening (D2–4 events). The ca 2670–2655 Ma D1 event represents a period of sagduction that occurred immediately after cessation of rifting as a result of gravitational instability from deposition of dense, cold, greenstone sequences onto thinned, light, hot felsic crust. Late basins represent depocentres on the sinking greenstones during sagduction. Marked contrasts in the structural style of gold deposits, metallogeny and fluid sources, typically attributed to progressive deformation during orogenesis, could instead reflect temporally distinct mineralising events during changing tectonic regimes. In the East Yilgarn, an early plumbing system dominated by north-northwest-trending basin-controlling structures was likely established during rifting and focused fluids during multiple hydrothermal circulation events.

Global Ocean Cooling of 2.3°C During the Last Glacial Maximum

AbstractQuantitative constraints on past mean ocean temperature (MOT) critically inform our historical understanding of Earth's energy balance. A recently developed MOT proxy based on paleoatmospheric Xe, Kr, and N2 ratios in ice core air bubbles is a promising tool rooted in the temperature dependences of gas solubilities. However, these inert gases are systematically undersaturated in the modern ocean interior, and it remains unclear how air‐sea disequilibrium may have changed in the past. Here, we carry out 30 tracer‐enabled model simulations under varying circulation, sea ice cover, and wind stress regimes to evaluate air‐sea disequilibrium in the Last Glacial Maximum (LGM) ocean. We find that undersaturation of all three gases was likely reduced, primarily due to strengthened high‐latitude winds, biasing reconstructed MOT by −0.38 ± 0.37°C (1σ). Accounting for air‐sea disequilibrium, paleoatmospheric inert gases indicate that LGM MOT was 2.27 ± 0.46°C (1σ) colder than the pre‐industrial era.

Tectonic activity in Gulf of Guinea and Sub-Sahara West Africa: A validation of Freeth (1977) using focal mechanism solutions

Fault plane solutions for a group of 104; 4.0 ≤ Mw ≤ 7.1 earthquakes between January 1979 and December 2016, extracted from the Global Centroid Moment Tensor Project catalog. Were used to investigate the regional tectonic stress regime of the Gulf of Guinea region. The idea is to validate the theory of membrane tectonics put forward by Freeth (1977)[1] in which the tectonic of the Gulf of Guinea and the sub-Sahara West Africa region were described based on Freeth (1977)[1]. The tectonic of the Gulf of Guinea and the sub-Sahara West Africa region are based on the movement of the African plate, we emphasized the use of rigorous statistical tests to decide on the quality and variability of the earthquake focal mechanisms (FMSs) utilized for the stress tensor inversion analysis. To constrain our analysis, we have applied both the Algorithm of Michael and Gauss technique in our stress tensor inversion analysis of FMS obtained from the region, and the results are found to be coherent and in good agreement with each other. Both Michael (1984)[2] and Zalohar and Vrabec (2007)[3] techniques show that the regional tectonic stress regime of the Gulf of Guinea and the sub-Sahara West Africa is extensional, which is in good agreement with the work of Freeth (1977)[1]. However, our investigation concluded that the orientation of the extensional stress regime is the same as the orientation of the movement of the African plate, which is towards the Euro-Asia plate.

Nonlinear Elastic Bottlebrush Polymer Hydrogels Modulate Actomyosin Mediated Protrusion Formation in Mesenchymal Stromal Cells.

The nonlinear elasticity of many tissue-specific extracellular matrices is difficult to recapitulate without the use of fibrous architectures, which couple strain-stiffening with stress relaxation. Herein, bottlebrush polymers are synthesized and crosslinked to form poly(ethylene glycol)-based hydrogels and used to study how strain-stiffening behavior affects human mesenchymal stromal cells (hMSCs). By tailoring the bottlebrush polymer length, the critical stress associated with the onset of network stiffening is systematically varied, and a unique protrusion-rich hMSC morphology emerges only at critical stresses within a biologically accessible stress regime. Local cell-matrix interactions are quantified using 3D traction force microscopy and small molecule inhibitors are used to identify cellular machinery that plays a critical role in hMSC mechanosensing of the engineered, strain-stiffening microenvironment. Collectively, this study demonstrates how covalently crosslinked bottlebrush polymer hydrogels can recapitulate strain-stiffening biomechanical cues at biologically relevant stresses and be used to probe how nonlinear elastic matrix properties regulate cellular processes.

The most relevant drought-tolerant indices for selecting barley drought-tolerant genotypes

During its development cycle, lack of water is one of the factors reducing plant growth and yields, in the world's arid regions. The identification of indices that characterize the most tolerant genotypes to drought is very useful since it allows us to evaluate the tolerance of large varieties collections within a short and early stage. This study aimed to identify the most efficient drought tolerance indicators and evaluate, from the early stage of plant development, the germination parameters that would be correlated with drought tolerance in the field. If such correlations were identified, it would be possible to screen dozens of genotypes in the laboratory and identify the most tolerant ones before moving into the field. To attain this objective, two tests were carried out: The first one was realized in the laboratory to assess some germination parameters (germination rate, root length, root number, etc.) of sixteen North African barley genotypes (Algerians, Tunisians, and Egyptians) at the germination stage, under polyethylene glycol (PEG-6000) induced stress. The second test was carried out in the field to measure the grain yield of the same genotypes, under favorable and limited water conditions. The laboratory test revealed significant differences between root lengths (RL) of different genotypes within each water regime and between different treatments (control and PEG-6000 solution). The obtained result showed the superiority of most Egyptian genotypes, especially under stress conditions induced by PEG-6000. The field trial also showed significant differences in grain yields under both water regimes (stressful and non-stressful regimes) and pointed to the high performance of the majority of Egyptian genotypes. The calculated indices [(STI), (SSI), (YSI), and (TOL)] showed variable correlations depending on the index used and concluded that STI and YSI are the best indicators of drought tolerance compared to the others. Among the germination parameters, only the root length (RL) under PEG stress is positively correlated with grain yield, obtained under drought conditions in the field. Therefore, it would be possible to use this parameter to select, at an early stage, the most drought-tolerant genotypes.

Stress Variations in Southern Tonga Slab Derived From Deep‐Focus Earthquakes

AbstractTonga is a convergent plate boundary between the Pacific and Australian plates and is the fastest and the most seismically active deep subduction system in the world. We focused on southern Tonga (south of latitude 22°S) and the mantle transition zone (depths of 410–670 km), where seismic activity forms two subparallel bands of events in the east and west. We performed stress analysis by inverting focal mechanisms of earthquakes available in the Global Centroid Moment Tensor catalog and revealed two distinct stress regimes in the slab. While the stress orientation in the eastern slab segment conforms to the down‐dip compressional stress along the entire slab, the stress orientation in the western slab segment is different, having the maximum compression in the vertical direction. This suggests that the western segment can represent a stagnant slab with flattening and bending, as proposed by modeling studies. Its connection with the younger actively subducting slab is supported by the horizontal westward shift at 520 km depth. The stress analysis also indicates substantially different fault orientations in both segments. In the actively dipping slab, the majority of activated faults are predominantly sub‐horizontal. However, they are significantly inclined from vertical in the stagnant slab segment. A higher scatter in fault orientations in the stagnant slab suggests deformation, fragmentation and rheological complexity resulting from bending and flattening.

Divergence Assessment of Advanced Bread Wheat Lines under Contrasting Heat Stress Regimes Utilizing Stress Tolerance Indices

Heat stress during the post-anthesis phase significantly impacts wheat cultivation. To evaluate the tolerance of advanced wheat lines to heat stress, stress tolerance indices were used under both normal and post-anthesis heat stress conditions. The results showed a decrease in the average yield of advanced lines under both conditions, indicating the negative impact of heat stress on wheat cultivation. The analysis using PCs, biplot, and ranked clusters revealed that line V-21448 had below-average values for RHSI and %YDR, while V-21243 had values close to the average and all other lines had above-average values. Additionally, under normal conditions, V-19532 had the highest values for RHSI and HYT 100-47 had the lowest values for %YDR. In heat stress conditions, HYT 100-47 had the lowest values for both indices. HYT 100-74 and HYT 100-76 had the highest average values for MNP and YDI and were highly stable in the heat environment. Under normal settings, YDI, RHSI, and % YDR showed a positive correlation, while under heat stress conditions, the same traits showed a negative correlation. MNP had a high positive correlation with Yp and Ys, while YDSI had a negative correlation with Yp but a positive correlation with Ys. These results suggest that these traits are useful for identifying advanced lines with increased yield under both conditions.

Mitigation of tunnel support design risks for hydropower projects within high tectonic stress regimes – an empirical analysis

Abstract The study for the design of tunnels in similar geological settings, providing insights into potential challenges that may arise during excavation and offering strategies for mitigating risks in District Kalam on the Ushu River, Khyber Pakhtunkhwa, Pakistan. The methodology involved geological mapping, rock sampling, discontinuity surveys, and laboratory testing for empirical analysis of tunnel parameters at the Weir House, Powerhouse, and tunnel alignment locations. Empirical analysis of tunnel parameters using three rock classification systems, rock mass rating (RMR), rock quality tunneling index, and rock mass index (RMi). Based on the classification, the rock quality was found to be fair, indicating favorable rock properties. The Q-system rated the rock as poor to fair, suggesting low discontinuity intensity, medium rock strength, or medium deformation modulus. According to the RMi, rock was rated as medium to strong, indicating low discontinuity intensity, high rock strength, or low deformability. The support design for the tunnel is based on empirical analysis, it recommends support design for the tunnel reinforcement elements such as rock bolts, wire mesh, and shotcrete lining. Overall, the tunnel is stable and does not have complex structure and weak zones.

Erratum to The Influence of a Transitional Stress Regime on the Source Characteristics of Induced Seismicity and Fault Activation: Evidence from the 30 November 2018 Fort St. John ML 4.5 Induced Earthquake Sequence

<i>Erratum to</i> The Influence of a Transitional Stress Regime on the Source Characteristics of Induced Seismicity and Fault Activation: Evidence from the 30 November 2018 Fort St. John ML 4.5 Induced Earthquake Sequence

Comparison and evaluation of overcoring and hydraulic fracturing stress measurements

The stress measurements determined by both the overcoring (OC) and hydraulic fracturing (HF) methods in the Shuichang iron mine and Sanshandao gold mine were compared and evaluated, respectively. The results indicate that the independent OC and HF data in the two mines reveal the same dominant faulting stress regime. The σH orientations derived from the OC and HF methods in the Shuichang iron mine are dominantly oriented in the N81.1°W–N89.4°W and N77.0°E–N88.0°E, respectively, and the σH orientations yielded from the OC and HF techniques in the Sanshandao gold mine are predominantly in the N30°W–N90°W and N55.5°W–N60.4°W, respectively; hence, the σH orientations obtained by the two different methods in the two mines are comparatively similar. In addition, the shapes of the probability density diagrams using an improved Bayesian regression approach of the three principal stresses measured by the OC and HF methods in the same mine are quite similar, and all the obtained Kolmogorov–Smirnov test p-values are larger than the selected significance level of 0.01, indicating that the stress data interpreted by the two methods approximately follow the same distribution law. Thus, the performance of the two techniques and the reliability of the measured data are satisfactory.

An integrated geomechanical and petrophysical multiparameter approach for gas reservoir evaluation

AbstractIntegrating petrophysical and geomechanical parameters is an efficient approach to evaluating shale gas reservoir potential. The high cost of corings and their limited number, coupled with time-intensive investigation, led researchers to use this alternative combination approach. In the Jiaoshiba area, from single-pilot well core data and log measurements, petrophysical and geomechanical parameters such as shale volume, total organic carbon, gas content, as well as pore pressure, stress components, and mineral brittleness were first estimated using established methods. In the second phase, based on logging curves, the reservoir electro-facies (EF) classification was performed using the unsupervised multi-resolution graph-based clustering method on a series of twenty wells, identifying five EF with different intrinsic characteristics. Unsupervised analyses were developed using the multilayer artificial neural network while incorporating the K-nearest neighbors and graphical classification algorithms. The results from the first and second phases indicate reservoir richness in organic matter, with the best reservoir exhibited by EF2 and EF3. In addition, effective stress components (SV, SH, and Sh) evaluation shows a normal stress regime with hydraulic fracture systems perpendicular to the minimum horizontal stress at each measured depth of the reservoir (Sv &gt; SH &gt; Sh). This research workflow can efficiently evaluate shale reservoirs with a realistic approach for identifying favorable fracturing positions while reducing errors due to human interference.

Imaging Left-Lateral and Reverse Near-Surface Slip of the 2020 Mw 5.1 Sparta, North Carolina, Earthquake

ABSTRACT Coseismic deformation of the 9 August 2020 Mw 5.1 Sparta, North Carolina, earthquake was captured by an Advanced Land Observing Satellite 2 interferogram, a Sentinel 1A/B interferogram, and differential light detection and ranging (lidar). Owing to the moderate surface deformation compared to the inherent uncertainties of interferometric data, the interferograms suffered from low signal-to-noise ratios, exacerbated by spurious signals arising from the discrepancy in resolution between the interferograms and digital elevation model used during processing. Nevertheless, coseismic slip can be imaged using graph-guided fused LASSO, where LASSO is the least-absolute shrinkage and selection operator—an inverse method that combines sparsity constraints and smoothness regularization—to infer signal from noisy and/or incomplete data. We develop five coseismic slip models, one determined only from the Sentinel 1A/B interferogram, one determined from both interferograms, one determined from all the Interferometric Synthetic Aperture Radar (InSAR) data masking potentially spurious data corresponding to industrial parks, one from lidar 3D displacements only, and one constrained by the masked InSAR and the lidar data. All five models are coseismic slip on a single fault plane, trending northwest–southeast with dips ranging from 41° to 60° to the southwest. Coseismic slip is imaged to be shallow, with predominantly oblique reverse slip extending to about 2 km depth. We find that masking the interferometric data corresponding to the industrial parks yields a coseismic slip model in better concordance with ancillary information about the Sparta earthquake and that the lidar data yield additional constraints on near-surface coseismic slip. We show that our preferred coseismic slip model is consistent with a stress regime that does not depart from an Andersonian thrust regime to a large degree, constraining that the background stress is larger than 20–30 MPa.

Integration of triaxial ultrasonic velocity and deformation rate analysis for core-based estimation of stresses at the Utah FORGE geothermal site

Core-based methods for in-situ stress estimation were applied using samples from 4 intervals within the Utah FORGE 16A(78)-32 well. At three of these locations, Triaxial Ultrasonic Velocity (TUV) tests were performed, resulting in experimentally-determined relationships between wave velocities and stresses. Non-monotonic increases in the velocity-stress relationships provide evidence of stress history and are therefore used to estimate in-situ stress magnitudes. Additionally, Deformation Rate Analysis (DRA) tests were run on core plugs from various orientations at each of the sampling locations. Results indicate the minimum stress gradient to be ∼0.61–0.74 psi/ft (14–17 kPa/m) and consistent with uniform tectonic strain of 150 microstrain in the Granitoid and tectonic strain that is around 50 % higher in the Gneiss than in the Granitoid. The vertical stress gradient is ∼ 1.09–1.12 psi/ft (24.7–25.3 kPa/m) for the two zones in which it could be inferred from data. The maximum stress gradient ∼ 0.90–1.01 psi/ft (20–23 kPa/m) in the granitoid and 1.32 psi/ft (30 kPa/m) in the Gneiss and consistent with tectonic strain around 300 microstrain through the Granitoid and over 900 microstrain in the Gneiss. The stress regime thus appears to be between normal faulting and strike-slip faulting, potentially becoming more strike-slip in nature with depth and/or flipping back and forth between the two regimes in the region penetrated by the well due to variability of rock properties, structures such as faults, and/or thermal anomalies. These are broadly consistent with other recently published stress models, and therefore provide valuable evidence to the stress state at the Utah FORGE geothermal site and a promising step in the direction of using TUV and DRA together as core-based stress estimation methods.

Potential distribution of Biscogniauxia mediterranea and Obolarina persica causal agents of oak charcoal disease in Iran’s Zagros forests

In Iran, native oak species are under threat from episodes of Charcoal Disease, a decline syndrome driven by abiotic stressors (e.g. drought, elevated temperature) and biotic components, Biscogniauxia mediterranea (De Not.) Kuntze and Obolarina persica (M. Mirabolfathy). The outbreak is still ongoing and the country’s largest ever recorded. Still, the factors driving its’ epidemiology in time and space are poorly known and such knowledge is urgently needed to develop strategies to counteract the adverse effects. In this study, we developed a generic framework based on experimental, machine-learning algorithms and spatial analyses for landscape-level prediction of oak charcoal disease outbreaks. Extensive field surveys were conducted during 2013–2015 in eight provinces (more than 50 unique counties) in the Zagros ecoregion. Pathogenic fungi were isolated and characterized through morphological and molecular approaches, and their pathogenicity was assessed under controlled water stress regimes in the greenhouse. Further, we evaluated a set of 29 bioclimatic, environmental, and host layers in modeling for disease incidence data using four well-known machine learning algorithms including the Generalized Linear Model, Gradient Boosting Model, Random Forest model (RF), and Multivariate Adaptive Regression Splines implemented in MaxEnt software. Model validation statistics [Area Under the Curve (AUC), True Skill Statistics (TSS)], and Kappa index were used to evaluate the accuracy of each model. Models with a TSS above 0.65 were used to prepare an ensemble model. The results showed that among the different climate variables, precipitation and temperature (Bio18, Bio7, Bio8, and bio9) in the case of O. persica and similarly, gsl (growing season length TREELIM, highlighting the warming climate and the endophytic/pathogenic nature of the fungus) and precipitation in case of B. mediterranea are the most important influencing variables in disease modeling, while near-surface wind speed (sfcwind) is the least important variant. The RF algorithm generates the most robust predictions (ROC of 0.95; TSS of 0.77 and 0.79 for MP and OP, respectively). Theoretical analysis shows that the ensemble model (ROC of 0.95 and 0.96; TSS = 0.79 and 0.81 for MP and OP, respectively), can efficiently be used in the prediction of the charcoal disease spatiotemporal distribution. The oak mortality varied ranging from 2 to 14%. Wood-boring beetles association with diseased trees was determined at 20%. Results showed that water deficiency is a crucial component of the oak decline phenomenon in Iran. The Northern Zagros forests (Ilam, Lorestan, and Kermanshah provinces) along with the southern Zagros forests (Fars and Kohgilouyeh va-Boyer Ahmad provinces) among others are the most endangered areas of potential future pandemics of charcoal disease. Our findings will significantly improve our understanding of the current situation of the disease to pave the way against pathogenic agents in Iran.

Effect of stress on fracture development in the Asmari reservoir in the Zagros Thrust Belt

Development and production from fractured reservoirs require extensive knowledge about the reservoir structures and in situ stress regimes. For this, this paper investigates fractures and the parameters (aperture and density) through a combination of wellbore data and geomechanical laboratory testing in three separate wells in the Asmari reservoir, Zagros Belt, Iran. The Asmari reservoir (Oligo-Miocene) consists mainly of calcitic and dolomitic rocks in depths of 2000-3000 m. Based on the observation of features in several wellbores, the orientation and magnitude of the in situ stresses along with their influence on reservoir-scale geological structures and neotectonics were determined. The study identifies two regional tectonic fracture settings in the reservoir: one set associated with longitudinal and diagonal wrinkling, and the other related to faulting. The former, which is mainly of open fractures with a large aperture, is dominant and generally oriented in the N45°-90°W direction while the latter is obliquely oriented relative to the bedding and characterized by N45°-90°E. The largest aperture is found in open fractures that are longitudinal and developed in the dolomitic zones within a complex stress regime. Moreover, analysis of drilling-induced fractures (DIFs) and borehole breakouts (BBs) from the image logs revealed that the maximum horizontal stress (SHmax) orientation in these three wells is consistent with the NE-SW regional trend of the SHmax (maximum principal horizontal stress) in the Zagros Belt. Likewise, the stress magnitude obtained from geomechanical testing and poroelastic equations confirmed a variation in stress regime from normal to reverse, which changes in regard to active faults in the study area. Finally, a relationship between the development degree of open fractures and in situ stress regime was found. This means that in areas where the stress regime is complex and reverse, fractures would exhibit higher density, dip angle, and larger apertures.