58 research outputs found
Hydraulic fracturingâinduced seismicity
Hydraulic fracturing (HF) is a technique that is used for extracting petroleum resources from impermeable host rocks. In this process, fluid injected under high pressure causes fractures to propagate. This technique has been transformative for the hydrocarbon industry, unlocking otherwise stranded resources; however, environmental concerns make HF controversial. One concern is HFâinduced seismicity, since fluids driven under high pressure also have the potential to reactivate faults. Controversy has inevitably followed these HFâinduced earthquakes, with economic and human losses from ground shaking at one extreme and moratoriums on resource development at the other. Here, we review the state of knowledge of this category of induced seismicity. We first cover essential background information on HF along with an overview of published induced earthquake cases to date. Expanding on this, we synthesize the common themes and interpret the origin of these commonalities, which include recurrent earthquake swarms, proximity to well bore, rapid response to stimulation, and a paucity of reported cases. Next, we discuss the unanswered questions that naturally arise from these commonalities, leading to potential research themes: consistent recognition of cases, proposed triggering mechanisms, geologically susceptible conditions, identification of operational controls, effective mitigation efforts, and scienceâinformed regulatory management. HFâinduced seismicity provides a unique opportunity to better understand and manage earthquake rupture processes; overall, understanding HFâinduced earthquakes is important in order to avoid extreme reactions in either direction
Indirect comparison of interventions using published randomised trials: systematic review of PDE-5 inhibitors for erectile dysfunction
BACKGROUND: There are no randomised and properly blinded trials directly comparing one PDE-5 inhibitor with another in a normal home setting. Valid indirect comparisons with a common comparator must examine equivalent doses, similar duration, similar populations, with the same outcomes reported in the same way. METHODS: Published randomised, double-blind trials of oral PDE-5 inhibitors for erectile dysfunction were sought from reference lists in previous reviews and electronic searching. Analyses of efficacy and harm were carried out for each treatment, and results compared where there was a common comparator and consistency of outcome reporting, using equivalent doses. RESULTS: Analysis was limited by differential reporting of outcomes. Sildenafil trials were clinically and geographically more diverse. Tadalafil and vardenafil trials tended to use enriched enrolment. Using all trials, the three interventions were similar for consistently reported efficacy outcomes. Rates of successful intercourse for sildenafil, tadalafil and vardenafil were 65%, 62%, and 59%, with placebo rates of 23â28%. The rates of improved erections were 76%, 75% and 71%, respectively, with placebo rates of 22â24%, and NNTs of 1.9 or 2.0. Reporting of withdrawals was less consistent, but all-cause withdrawals for sildenafil, tadalafil and vardenafil were 8% 13% and 20%. All three drugs were well tolerated, with headache being the most commonly reported event at 13â17%. There were few serious adverse events. CONCLUSION: There were differences between trials in outcomes reported, limiting comparisons, and the most useful outcomes were not reported. For common outcomes there was similar efficacy between PDE-5 inhibitors
FractureâMesh Faulting in the SwarmâLike 2020 Maacama Sequence Revealed by HighâPrecision Earthquake Detection, Location, and Focal Mechanisms
Abstract In August of 2020, an earthquake sequence initiated within the Maacama fault zone in northern California, raising questions about its relationship with the largerâscale fault. To investigate the faulting geometry and its implications for physical processes driving seismicity, we applied an integrated, multiâfaceted seismic analysis including waveformâcorrelationâbased event detection, relative relocation, and highâprecision focal mechanisms. To determine mechanisms for a large population of very small earthquakes (predominantly MÂ <Â 1), we combined correlationâderived polarity analysis with a recently developed technique to determine S/P amplitude ratios from single seismic components. Finally, we applied an iterative stress inversion to distinguish between the likely fault and auxiliary planes. This analysis reveals that although the sequence initiated on a rightâlateral fault, plausibly a strand of the Maacama Fault, it also activated numerous en echelon leftâlateral conjugate faults. Together, these interlocking faults form a fracture mesh, consistent with structures associated elsewhere with fluidâinduced faulting and earthquake swarms
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