An improved framework for discriminating seismicity induced by industrial activities from natural earthquakes

Heightened concerns regarding induced seismicity necessitate robust methods to assess whether detected earthquakes near industrial sites are natural or induced by the industrial activity. These assessments are required rapidly, which often precludes detailed modeling of fluid pressures and the geomechanical response of the reservoir and nearby faults. Simple question‐based assessment schemes in current use are a useful tool but suffer from several shortcomings: they do not specifically address questions regarding whether available evidence supports the case for natural seismicity; they give all questions equal weighting regardless of the relative influence of different factors; they are not formulated to account for ambiguous or uncertain evidence; and the final outcomes can be difficult to interpret. We propose a new framework that addresses these shortcomings by assigning numerical scores to each question, with positive values for answers that support induced seismicity and negative values for responses favoring natural seismicity. The score values available for each question reflect the relative importance of the different questions, and for each question the absolute value of the score is modulated according to the degree of uncertainty. The final outcome is a score, the induced assessment ratio, either positive or negative (or zero), that reflects whether events were induced or natural. A second score, the evidence strength ratio, is assigned that characterizes the strength of the available evidence, expressed as the ratio of the maximum score possible with the available evidence relative to the maximum score that could be obtained if all desired data were available at a site. We demonstrate this approach by application to two case studies in the United Kingdom, one widely regarded as a case of induced seismicity, and the other more likely to be a series of tectonic earthquakes

Coupled poroelastic modelling of hydraulic fracturing-induced seismicity: Implications for understanding the post shut-in ML 2.9 earthquake at the Preston New Road, UK

Post-injection seismicity associated with hydraulic stimulation has posed great challenges to hydraulic fracturing operations. This work aims to identify the causal mechanism of the post shut-in ML 2.9 earthquake in August 2019 at the Preston New Road, UK, amongst three plausible mechanisms, i.e., the post shut-in pore pressure diffusion, poroelastic stressing on a non-overpressurised fault, and poroelastic stressing on an overpressurised fault. A 3D fully-coupled poroelastic model that considers the poroelastic solid deformation, fluid flow in both porous rocks and fracture structures, and hydraulic fracture propagation was developed to simulate the hydromechanical response of the shale reservoir formation to hydraulic fracturing operations at the site. Based on the model results, Coulomb stress changes and seismicity rate were further evaluated on the PNR-2 fault responsible for the earthquake. Model results have shown that increased pore pressure plays a dominant role in triggering the fault slippage, although the poroelastic stress may have acted to promote the slippage. Amongst the three plausible mechanisms, the post shut-in pore pressure diffusion is the most favoured in terms of Coulomb stress change, seismicity rate, timing of fault slippage and rupture area. The coupled modelling results suggested that the occurrence of the post shut-in ML 2.9 earthquake was a three-staged process, involving first propagation of fracture tips that stimulated surrounding reservoir formations, then hydraulic connection with and subsequent pore pressure diffusion to the partially-sealing PNR-2 fault, and eventually fault activation primarily under the direct impact of increased pore pressure

Green, yellow, red, or out of the blue? An assessment of Traffic Light Schemes to mitigate the impact of hydraulic fracturing-induced seismicity

Mitigating hydraulic fracturing-induced seismicity (HF-IS) poses a challenge for shale gas companies and regulators alike. The use of Traffic Light Schemes (TLSs) is the most common way by which the hazards associated with HF-IS are mitigated. In this study, we discuss the implicit risk mitigation objectives of TLSs and explain the advantages of magnitude as the fundamental parameter to characterise induced seismic hazard. We go on to investigate some of the key assumptions on which TLSs are based, namely that magnitudes evolve relatively gradually from green to yellow to red thresholds (as opposed to larger events occurring “out-of-the-blue”), and that trailing event magnitudes do not increase substantially after injection stops. We compile HF-IS datasets from around the world, including the USA, Canada, the UK, and China, and track the temporal evolution of magnitudes in order to evaluate the extent to which magnitude jumps (i.e. sharp increases in magnitude from preceding events within a sequence) and trailing events occur. We find in the majority of cases magnitude jumps are less than 2 units. One quarter of cases experienced a post-injection magnitude increase, with the largest being 1.6. Trailing event increases generally occurred soon after injection, with most cases showing no increase in magnitude more than a few days after then end of injection. Hence, the effective operation of TLSs may require red-light thresholds to be set as much as two magnitude units below the threshold that the scheme is intended to avoid

Water, oceanic fracture zones and the lubrication of subducting plate boundaries - insights from seismicity

We investigate the relationship between subduction processes and related seismicity for the Lesser Antilles Arc using the Gutenberg-Richter law. This power lawdescribes the earthquakemagnitude distribution, with the gradient of the cumulative magnitude distribution being commonly known as the b-value. The Lesser Antilles Arc was chosen because of its alongstrike variability in sediment subduction and the transition from subduction to strike-slip movement towards its northern and southern ends. The data are derived from the seismicity catalogues from the Seismic Research Centre of The University of the West Indies and the Observatoires Volcanologiques et Sismologiques of the Institut de Physique du Globe de Paris and consist of subcrustal events primarily from the slab interface. The b-value is found using a Kolmogorov-Smirnov test for a maximum-likelihood straight line-fitting routine. We investigate spatial variations in b-values using a grid-search with circular cells as well as an along-arc projection. Tests with different algorithms and the two independent earthquake cataloges provide confidence in the robustness of our results. We observe a strong spatial variability of the b-value that cannot be explained by the uncertainties. Rather than obtaining a simple north-south b-value distribution suggestive of the dominant control on earthquake triggering being water released from the sedimentary cover on the incoming American Plates, or a b-value distribution that correlates with on the obliquity of subduction, we obtain a series of discrete, high b-value 'bull's-eyes' along strike. These bull's-eyes, which indicate stress release through a higher fraction of small earthquakes, coincide with the locations of known incoming oceanic fracture zones on the American Plates. We interpret the results in terms of water being delivered to the Lesser Antilles subduction zone in the vicinity of fracture zones providing lubrication and thus changing the character of the related seismicity. Our results suggest serpentinization around mid-ocean ridge transform faults, which go on to become fracture zones on the incoming plate, plays a significant role in the delivery of water into the mantle at subduction zones

Reservoir stress path and induced seismic anisotropy: Results from linking coupled fluid-flow/geomechanical simulation with seismic modelling

We present a workflow linking coupled fluid-flow and geomechanical simulation with seismic modelling to predict seismic anisotropy induced by nonhydrostatic stress changes. We generate seismic models from coupled simulations to examine the relationship between reservoir geometry, stress path and seismic anisotropy. The results indicate that geometry influences the evolution of stress, which leads to stress-induced seismic anisotropy. Although stress anisotropy is high for the small reservoir, the effect of stress arching and the ability of the side-burden to support the excess load limit the overall change in effective stress and hence seismic anisotropy. For the extensive reservoir, stress anisotropy and induced seismic anisotropy are high. The extensive and elongate reservoirs experience significant compaction, where the inefficiency of the developed stress arching in the side-burden cannot support the excess load. The elongate reservoir displays significant stress asymmetry, with seismic anisotropy developing predominantly along the long-edge of the reservoir. We show that the link between stress path parameters and seismic anisotropy is complex, where the anisotropic symmetry is controlled not only by model geometry but also the nonlinear rock physics model used. Nevertheless, a workflow has been developed to model seismic anisotropy induced by non-hydrostatic stress changes, allowing field observations of anisotropy to be linked with geomechanical models

Gender differences in presentation and diagnosis of chest pain in primary care

<p>Abstract</p> <p>Background</p> <p>Chest pain is a common complaint and reason for consultation in primary care. Research related to gender differences in regard to Coronary Heart Disease (CHD) has been mainly conducted in hospital but not in primary care settings. We aimed to analyse gender differences in aetiology and clinical characteristics of chest pain and to provide gender related symptoms and signs associated with CHD.</p> <p>Methods</p> <p>We included 1212 consecutive patients with chest pain aged 35 years and older attending 74 general practitioners (GPs). GPs recorded symptoms and findings of each patient and provided follow up information. An independent interdisciplinary reference panel reviewed clinical data of every patient and decided about the aetiology of chest pain at the time of patient recruitment. Multivariable regression analysis was performed to identify clinical predictors that help to rule in or out CHD in women and men.</p> <p>Results</p> <p>Women showed more psychogenic disorders (women 11,2%, men 7.3%, p = 0.02), men suffered more from CHD (women 13.0%, men 17.2%, p = 0.04), trauma (women 1.8%, men 5.1%, p < 0.001) and pneumonia/pleurisy (women 1.3%, men 3.0%, p = 0.04) Men showed significantly more often chest pain localised on the right side of the chest (women 9.1%, men 25.0%, p = 0.01). For both genders known clinical vascular disease, pain worse with exercise and age were associated positively with CHD. In women pain duration above one hour was associated positively with CHD, while shorter pain durations showed an association with CHD in men. In women negative associations were found for stinging pain and in men for pain depending on inspiration and localised muscle tension.</p> <p>Conclusions</p> <p>We found gender differences in regard to aetiology, selected clinical characteristics and association of symptoms and signs with CHD in patients presenting with chest pain in a primary care setting. Further research is necessary to elucidate whether these differences would support recommendations for different diagnostic approaches for CHD according to a patient's gender.</p

A Modified RMCE-Compatible Rosa26 Locus for the Expression of Transgenes from Exogenous Promoters

Generation of gain-of-function transgenic mice by targeting the Rosa26 locus has been established as an alternative to classical transgenic mice produced by pronuclear microinjection. However, targeting transgenes to the endogenous Rosa26 promoter results in moderate ubiquitous expression and is not suitable for high expression levels. Therefore, we now generated a modified Rosa26 (modRosa26) locus that combines efficient targeted transgenesis using recombinase-mediated cassette exchange (RMCE) by Flipase (Flp-RMCE) or Cre recombinase (Cre-RMCE) with transgene expression from exogenous promoters. We silenced the endogenous Rosa26 promoter and characterized several ubiquitous (pCAG, EF1α and CMV) and tissue-specific (VeCad, αSMA) promoters in the modRosa26 locus in vivo. We demonstrate that the ubiquitous pCAG promoter in the modRosa26 locus now offers high transgene expression. While tissue-specific promoters were all active in their cognate tissues they additionally led to rare ectopic expression. To achieve high expression levels in a tissue-specific manner, we therefore combined Flp-RMCE for rapid ES cell targeting, the pCAG promoter for high transgene levels and Cre/LoxP conditional transgene activation using well-characterized Cre lines. Using this approach we generated a Cre/LoxP-inducible reporter mouse line with high EGFP expression levels that enables cell tracing in live cells. A second reporter line expressing luciferase permits efficient monitoring of Cre activity in live animals. Thus, targeting the modRosa26 locus by RMCE minimizes the effort required to target ES cells and generates a tool for the use exogenous promoters in combination with single-copy transgenes for predictable expression in mice

Chest pain in primary care: is the localization of pain diagnostically helpful in the critical evaluation of patients? - A cross sectional study

BACKGROUND: Chest pain is a common complaint and reason for consultation in primary care. Traditional textbooks still assign pain localization a certain discriminative role in the differential diagnosis of chest pain. The aim of our study was to synthesize pain drawings from a large sample of chest pain patients and to examine whether pain localizations differ for different underlying etiologies. METHODS: We conducted a cross-sectional study including 1212 consecutive patients with chest pain recruited in 74 primary care offices in Germany. Primary care providers (PCPs) marked pain localization and radiation of each patient on a pictogram. After 6 months, an independent interdisciplinary reference panel reviewed clinical data of every patient, deciding on the etiology of chest pain at the time of patient recruitment. PCP drawings were entered in a specially designed computer program to produce merged pain charts for different etiologies. Dissimilarities between individual pain localizations and differences on the level of diagnostic groups were analyzed using the Hausdorff distance and the C-index. RESULTS: Pain location in patients with coronary heart disease (CHD) did not differ from the combined group of all other patients, including patients with chest wall syndrome (CWS), gastro-esophageal reflux disease (GERD) or psychogenic chest pain. There was also no difference in chest pain location between male and female CHD patients. CONCLUSIONS: Pain localization is not helpful in discriminating CHD from other common chest pain etiologies

The Geomechanics of CO2 Storage in Deep Sedimentary Formations

This paper provides a review of the geomechanics and modeling of geomechanics associated with geologic carbon storage (GCS), focusing on storage in deep sedimentary formations, in particular saline aquifers. The paper first introduces the concept of storage in deep sedimentary formations, the geomechanical processes and issues related with such an operation, and the relevant geomechanical modeling tools. This is followed by a more detailed review of geomechanical aspects, including reservoir stress-strain and microseismicity, well integrity, caprock sealing performance, and the potential for fault reactivation and notable (felt) seismic events. Geomechanical observations at current GCS field deployments, mainly at the In Salah CO2 storage project in Algeria, are also integrated into the review. The In Salah project, with its injection into a relatively thin, low-permeability sandstone is an excellent analogue to the saline aquifers that might be used for large scale GCS in parts of Northwest Europe, the U.S. Midwest, and China. Some of the lessons learned at In Salah related to geomechanics are discussed, including how monitoring of geomechanical responses is used for detecting subsurface geomechanical changes and tracking fluid movements, and how such monitoring and geomechanical analyses have led to preventative changes in the injection parameters. Recently, the importance of geomechanics has become more widely recognized among GCS stakeholders, especially with respect to the potential for triggering notable (felt) seismic events and how such events could impact the long-term integrity of a CO{sub 2} repository (as well as how it could impact the public perception of GCS). As described in the paper, to date, no notable seismic event has been reported from any of the current CO{sub 2} storage projects, although some unfelt microseismic activities have been detected by geophones. However, potential future commercial GCS operations from large power plants will require injection at a much larger scale. For such largescale injections, a staged, learn-as-you-go approach is recommended, involving a gradual increase of injection rates combined with continuous monitoring of geomechanical changes, as well as siting beneath a multiple layered overburden for multiple flow barrier protection, should an unexpected deep fault reactivation occur