A New Paradigm for Large Earthquakes in Stable Continental Plate Interiors

Large earthquakes within stable continental regions (SCR) show that significant amounts of elastic strain can be released on geological structures far from plate boundary faults, where the vast majority of the Earth's seismic activity takes place. SCR earthquakes show spatial and temporal patterns that differ from those at plate boundaries and occur in regions where tectonic loading rates are negligible. However, in the absence of a more appropriate model, they are traditionally viewed as analogous to their plate boundary counterparts, occuring when the accrual of tectonic stress localized at long-lived active faults reaches failure threshold. Here we argue that SCR earthquakes are better explained by transient perturbations of local stress or fault strength that release elastic energy from a pre-stressed lithosphere. As a result, SCR earthquakes can occur in regions with no previous seismicity and no surface evidence for strain accumulation. They need not repeat, since the tectonic loading rate is close to zero. Therefore, concepts of recurrence time or fault slip rate do not apply. As a consequence, seismic hazard in SCRs is likely more spatially distributed than indicated by paleoearthquakes, current seismicity, or geodetic strain rates

Evaluation of polymyxin B in combination with 13 other antibiotics against carbapenemase-producing Klebsiella pneumoniae in time-lapse microscopy and time-kill experiments

Objectives: This study aimed to explore the interactions of polymyxin B in combination with 13 other antibiotics against carbapenemase-producing Klebsiella pneumoniae. Methods: Five clinical isolates of multidrug-resistant K. pneumoniae producing KPC-2, KPC-3, NDM-1, OXA-48 and VIM-1 carbapenemases were used. Polymyxin B was tested alone and in combination with amikacin, aztreonam, cefepime, chloramphenicol, ciprofloxacin, fosfomycin, linezolid, meropenem, minocycline, rifampicin, temocillin, thiamphenicol and trimethoprim. Inhibition of growth during antibiotic exposure was evaluated in 24-hr automated time-lapse microscopy experiments. Combinations that showed positive interactions were subsequently evaluated in static time-kill experiments. Results: All strains carried multiple (>9) resistance genes as determined by whole-genome sequencing. In the initial screening the combination of polymyxin B and minocycline was most active with enhanced activity compared with the single antibiotics detected against all strains. Positive interactions were also observed with polymyxin B in combination with rifampicin and fosfomycin against four of five strains and less frequently with other antibiotics. Time-kill experiments demonstrated an additive or synergistic activity (1-2 log10 or >= 2 log(10) CFU/mL reduction, respectively, compared with the most potent single antibiotic) with 21 of 23 tested combinations. However, because of regrowth, only 13 combinations were synergistic at 24 hr. Combinations with minocycline or rifampicin were most active, each showing synergy and bacteriostatic or bactericidal effects resulting in 1.93-3.97 and 2.55-5.91 log(10) CFU/mL reductions, respectively, after 24 hr against four strains. Discussion: Polymyxin B in combination with minocycline, rifampicin or fosfomycin could be of potential clinical interest. Time-lapse microscopy showed some discrepancy in results compared with the time-kill data but was useful for screening purposes

Evidence for the release of long-term tectonic strain stored in continental interiors through intraplate earthquakes

The occurrence of large earthquakes in stable continental interiors challenges the applicability of the classical steady-state ‘seismic cycle’ model to such regions. Here, we shed new light onto this issue using as a case study the cluster of large reverse faulting earthquakes that occurred in Fennoscandia at 11-9 ka, triggered by the removal of the ice load during the final phase of regional deglaciation. We show that these reverse-faulting earthquakes occurred at a time when the horizontal strain-rate field was extensional, which implies that these events did not release horizontal strain that was building up at the time, but compressional strain that had been accummulated and stored elastically in the lithosphere over timescales similar to or longer than a glacial cycle. We argue that the tectonically-stable continental lithosphere can store elastic strain on long timescales, the release of which may be triggered by rapid, local transient stress changes caused by surface mass redistribution, resulting in the occurrence of intermittent intraplate earthquakes