Cycle sismique et déformation continentale le long de la subduction Péruvienne

The Nazca/South American subduction zone is one of the most active regions on Earth. Large earthquakes and associated tsunamis occur recurrently almost all along its margin. Nevertheless, the ~1000 km long (from lat.2oS to 9oS) segment in northern Peru and southern Ecuador subduction has remained in relative seismic silence for at least the past five centuries. Before the work presented in this thesis, no information about the processes accommodating the convergence was available for this region and it was impossible to answer whether it could host a great Mw>8.5 earthquake in future or not. Nowadays, spatial geodesy, and more specifically GPS/GNSS enable us to quantify the surface displacement on the overriding plate with millimeter accuracy. Geodetic measurements together with the use of elastic models allow us to determine the amount of interseismic coupling at the plate interface. My thesis focuses on the seismic cycle and the continental deformation along the Peruvian subduction margin, with particular interest along its northern and central segments. We use GPS measurements acquired since 2008 in the frame of an international French-Peruvian- Ecuadorian project (the Andes Du Nord project, ADN). Our GPS velocity field covers the entire Peruvian subduction margin, with measurements in the Andean cordillera and part of the sub-Andean region. Modeling of GPS velocity field show the existence of a new tectonic microplate that we baptized as the Inca Sliver, which is in southeastward translation a rate of 4-5 mm/yr with respect to stable South America.La zone de subduction entre les plaques Nazca et Amérique du Sud est une des régions les plus actives de notre planète. De grands tremblements de terre et tsunamis associés se produisent de façon récurrente presque tout au long de sa marge. Néanmoins, le segment de subduction au nord du Pérou (de lat.3oS à 9oS) est resté le seul segment sismiquement silencieux depuis les premières informations historiques sur les séismes qui remontent au XVème siècle. Avant les travaux présentés dans ce manuscrit, aucune information sur les processus accommodant la convergence de la plaque Nazca vers le continent Sud-Américain n’était disponible le long du segment de 1000km au nord Pérou et sud Equateur. Les techniques de géodésie spatiale, en particulier le GPS/GNSS, nous permettent de quantifier les mouvements à la surface de la plaque supérieure avec une précision millimétrique. Ces mesures, couplées à l'utilisation de modèles élastiques, nous permettent de déterminer le niveau du couplage intersismique le long de l'interface entre les plaques. Le but de ma thèse est d'étudier le cycle sismique et la déformation continentale le long de la zone de subduction du Pérou, avec un intérêt particulier pour son segment nord. Nous utilisons des mesures GPS acquises depuis 2008 dans le cadre d'un projet international (le projet Andes Du Nord, ANR- ADN). Le champ de vitesse GPS obtenu couvre l’ensemble de la marge de subduction péruvienne, avec des mesures dans la cordillère et dans une moindre mesure dans la région sub-Andine. L'analyse et la modélisation du champ de vitesse GPS ont permis d'obtenir les résultats suivants: Premièrement: nous mettons en évidence l'existence d'un nouveau domaine continental, que nous avons baptisé comme le sliver Inca et qui est en translation a une vitesse de 4-5 mm/an en direction sud-est par rapport au craton Sud Américain. Le sliver Inca s’étend tout le long de la marge péruvienne

Bayesian parameter estimation for space and time interacting earthquake rupture model using historical and physics-based simulated earthquake catalogs

This paper presents a robust parameter estimation technique for a probabilistic earthquake hazard model that captures time and space interactions between earthquake mainshocks. The approach addresses the existing limitations of parameter estimation techniques by developing a Bayesian formulation and leveraging physics-based simulated synthetic catalogs to expand the limited datasets of historical catalogs. The technique is based on a two-step Bayesian update that uses the synthetic catalog to perform a first parameter estimation and then uses the historical catalog to further calibrate the parameters. We applied this technique to analyze the occurrence of large-magnitude interface earthquakes along 650 km of the central subduction zone in Peru, located offshore of Lima. We built 2,000-years-long synthetic catalogs using quasi-dynamic earthquake cycle simulations based on the rate-and-state friction law. The validity of the synthetic catalogs was verified by comparing their annual magnitude exceedence rates to those of recorded seismicity and their predicted areas of high interseismic coupling to those inferred from geodetic data. We show that when the Bayesian update uses the combination of synthetic and historical data, instead of only the historical data, it reduces the uncertainty of model parameter estimates by 45% on average. Further, our results show that the time-dependent seismic hazard estimated with the both datasets is 40% smaller than the one estimated with only the historical data

Bayesian parameter estimation for space and time interacting earthquake rupture model using historical and physics-based simulated earthquake catalogs

This paper presents a robust parameter estimation technique for a probabilistic earthquake hazard model that captures time and space interactions between earthquake mainshocks. The approach addresses the existing limitations of parameter estimation techniques by developing a Bayesian formulation and leveraging physics-based simulated synthetic catalogs to expand the limited datasets of historical catalogs. The technique is based on a two-step Bayesian update that uses the synthetic catalog to perform a first parameter estimation and then uses the historical catalog to further calibrate the parameters. We applied this technique to analyze the occurrence of large-magnitude interface earthquakes along 650 km of the central subduction zone in Peru, located offshore of Lima. We built 2,000-years-long synthetic catalogs using quasi-dynamic earthquake cycle simulations based on the rate-and-state friction law. The validity of the synthetic catalogs was verified by comparing their annual magnitude exceedence rates to those of recorded seismicity and their predicted areas of high interseismic coupling to those inferred from geodetic data. We show that when the Bayesian update uses the combination of synthetic and historical data, instead of only the historical data, it reduces the uncertainty of model parameter estimates by 45% on average. Further, our results show that the time-dependent seismic hazard estimated with the both datasets is 40% smaller than the one estimated with only the historical data

Aftershocks driven by afterslip and fluid pressure sweeping through a fault‐fracture mesh

A variety of physical mechanisms are thought to be responsible for the triggering and spatiotemporal evolution of aftershocks. Here we analyze a vigorous aftershock sequence and postseismic geodetic strain that occurred in the Yuha Desert following the 2010 Mw 7.2 El Mayor‐Cucapah earthquake. About 155,000 detected aftershocks occurred in a network of orthogonal faults and exhibit features of two distinct mechanisms for aftershock triggering. The earliest aftershocks were likely driven by afterslip that spread away from the main shock with the logarithm of time. A later pulse of aftershocks swept again across the Yuha Desert with square root time dependence and swarm‐like behavior; together with local geological evidence for hydrothermalism, these features suggest that the events were driven by fluid diffusion. The observations illustrate how multiple driving mechanisms and the underlying fault structure jointly control the evolution of an aftershock sequence

A nonplanar slow rupture episode during the 2000 Miyakejima dike intrusion

Magmatic intrusions release extensional strain in the Earth's crust upon availability of magma. Intrusions are typically accompanied by earthquake swarms and by surface faulting that is often larger than what is expected from the magnitude of the induced earthquakes. The 2000 Miyakejima dike intrusion triggered the largest volcanic earthquake swarm monitored so far, with five Ml>6 earthquakes. We analyze the seismicity and deformation induced by the Miyakejima dike with the aim of constraining the timescale and mechanisms of slow strain release during the episode. In six earthquake bursts lasting few hours and migrating at 3c1 km h 121 we find candidates for slow earthquakes. Each burst nucleated at the tips of previous bursts, suggesting stress interaction. The variability of fault plane solutions indicates that the bursts occurred on a complex system of fractures, consistent with weakly consolidated surface layers strained by spatially inhomogneous stresses that change in time, such as those induced by a dike. Based on dislocation models, we find that deformation is best explained by aseismic slip (in addition to the seismic burst), with a moment 1.3 to 2.3 times larger than the earthquakes' seismic moment, and opening of 0.20 \ub1 0.07 m on the dike. The aseismic slip occurred over a few hours, with moment, duration, and migration velocity consistent with that of previously observed slow slip events. We argue that the seismic bursts are likely driven by slow slip, sharing most properties with tectonic slow slip events and swarms, but occurring on a set of nonaligned faults

Extension and Dynamics of the Andes inferred from the 2016 Parina (Huarichancara) Earthquake

The M w 6.1 2016 Parina earthquake led to extension of the south Peruvian Andes along a normal fault with evidence of Holocene slip. We use InSAR, seismology and field mapping to determine a source model for this event and show that extension at Parina is oriented NE-SW, which is parallel to the shortening direction in the adjacent sub-Andean lowlands. In addition, we use earthquake source models and GPS data to demonstrate that shortening within the sub-Andes is parallel to topographic gradients. Both observations imply that forces resulting from spatial variations in gravitational potential energy are important in controlling the geometry of the deformation in the Andes. We calculate 9 the horizontal forces per unit length acting between the Andes and South America due to these potential energy contrasts to be 4 − 8 × 10 12 N per metre along-strike of the mountain range. Normal faulting at Parina implies that the Andes in south Peru have reached the maximum elevation that can be supported by the forces transmitted across the adjacent foreland, which requires that the foreland faults have an effective coefficient of friction <0.2. Additionally, the onset of extension in parts of the central Andes following orogen-wide compression in the late Miocene suggests there has been a change in the force balance within the mountains. We propose that shortening on weak detachment faults within the Andean foreland since ∼5-9 Ma reduced the shear tractions acting along the base of the upper crust in the eastern Andes, leading to extension in the highest parts of the range

Effectiveness of dietary interventions among adults of retirement age: a systematic review and meta-analysis of randomized controlled trials

Background Retirement from work involves significant lifestyle changes and may represent an opportunity to promote healthier eating patterns in later life. However, the effectiveness of dietary interventions during this period has not been evaluated. Methods We undertook a systematic review of dietary interventions among adults of retirement transition age (54 to 70 years). Twelve electronic databases were searched for randomized controlled trials evaluating the promotion of a healthy dietary pattern, or its constituent food groups, with three or more months of follow-up and reporting intake of specific food groups. Random-effects models were used to determine the pooled effect sizes. Subgroup analysis and meta-regression were used to assess sources of heterogeneity. Results Out of 9,048 publications identified, 68 publications reporting 24 studies fulfilled inclusion criteria. Twenty-two studies, characterized by predominantly overweight and obese participants, were included in the meta-analysis. Overall, interventions increased fruit and vegetable (F&V) intake by 87.5 g/day (P <0.00001), with similar results in the short-to-medium (that is, 4 to 12 months; 85.6 g/day) and long-term (that is, 13 to 58 months; 87.0 g/day) and for body mass index (BMI) stratification. Interventions produced slightly higher intakes of fruit (mean 54.0 g/day) than of vegetables (mean 44.6 g/day), and significant increases in fish (7 g/day, P = 0.03) and decreases in meat intake (9 g/day, P <0.00001). Conclusions Increases in F&V intakes were positively associated with the number of participant intervention contacts. Dietary interventions delivered during the retirement transition are therefore effective, sustainable in the longer term and likely to be of public health significance

Reduction in saturated fat intake for cardiovascular disease

BACKGROUND: Reducing saturated fat reduces serum cholesterol, but effects on other intermediate outcomes may be less clear. Additionally, it is unclear whether the energy from saturated fats eliminated from the diet are more helpfully replaced by polyunsaturated fats, monounsaturated fats, carbohydrate or protein. OBJECTIVES: To assess the effect of reducing saturated fat intake and replacing it with carbohydrate (CHO), polyunsaturated (PUFA), monounsaturated fat (MUFA) and/or protein on mortality and cardiovascular morbidity, using all available randomised clinical trials. SEARCH METHODS: We updated our searches of the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid) and Embase (Ovid) on 15 October 2019, and searched Clinicaltrials.gov and WHO International Clinical Trials Registry Platform (ICTRP) on 17 October 2019. SELECTION CRITERIA: Included trials fulfilled the following criteria: 1) randomised; 2) intention to reduce saturated fat intake OR intention to alter dietary fats and achieving a reduction in saturated fat; 3) compared with higher saturated fat intake or usual diet; 4) not multifactorial; 5) in adult humans with or without cardiovascular disease (but not acutely ill, pregnant or breastfeeding); 6) intervention duration at least 24 months; 7) mortality or cardiovascular morbidity data available. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed inclusion, extracted study data and assessed risk of bias. We performed random-effects meta-analyses, meta-regression, subgrouping, sensitivity analyses, funnel plots and GRADE assessment. MAIN RESULTS: We included 15 randomised controlled trials (RCTs) (16 comparisons, ~59,000 participants), that used a variety of interventions from providing all food to advice on reducing saturated fat. The included long-term trials suggested that reducing dietary saturated fat reduced the risk of combined cardiovascular events by 21% (risk ratio (RR) 0.79; 95% confidence interval (CI) 0.66 to 0.93, 11 trials, 53,300 participants of whom 8% had a cardiovascular event, I² = 65%, GRADE moderate-quality evidence). Meta-regression suggested that greater reductions in saturated fat (reflected in greater reductions in serum cholesterol) resulted in greater reductions in risk of CVD events, explaining most heterogeneity between trials. The number needed to treat for an additional beneficial outcome (NNTB) was 56 in primary prevention trials, so 56 people need to reduce their saturated fat intake for ~four years for one person to avoid experiencing a CVD event. In secondary prevention trials, the NNTB was 32. Subgrouping did not suggest significant differences between replacement of saturated fat calories with polyunsaturated fat or carbohydrate, and data on replacement with monounsaturated fat and protein was very limited. We found little or no effect of reducing saturated fat on all-cause mortality (RR 0.96; 95% CI 0.90 to 1.03; 11 trials, 55,858 participants) or cardiovascular mortality (RR 0.95; 95% CI 0.80 to 1.12, 10 trials, 53,421 participants), both with GRADE moderate-quality evidence. There was little or no effect of reducing saturated fats on non-fatal myocardial infarction (RR 0.97, 95% CI 0.87 to 1.07) or CHD mortality (RR 0.97, 95% CI 0.82 to 1.16, both low-quality evidence), but effects on total (fatal or non-fatal) myocardial infarction, stroke and CHD events (fatal or non-fatal) were all unclear as the evidence was of very low quality. There was little or no effect on cancer mortality, cancer diagnoses, diabetes diagnosis, HDL cholesterol, serum triglycerides or blood pressure, and small reductions in weight, serum total cholesterol, LDL cholesterol and BMI. There was no evidence of harmful effects of reducing saturated fat intakes. AUTHORS' CONCLUSIONS: The findings of this updated review suggest that reducing saturated fat intake for at least two years causes a potentially important reduction in combined cardiovascular events. Replacing the energy from saturated fat with polyunsaturated fat or carbohydrate appear to be useful strategies, while effects of replacement with monounsaturated fat are unclear. The reduction in combined cardiovascular events resulting from reducing saturated fat did not alter by study duration, sex or baseline level of cardiovascular risk, but greater reduction in saturated fat caused greater reductions in cardiovascular events

Earthquake cycle and continental deformation along the Peruvian subduction zone

La zone de subduction entre les plaques Nazca et Amérique du Sud est une des régions les plus actives de notre planète. De grands tremblements de terre et tsunamis associés se produisent de façon récurrente presque tout au long de sa marge. Néanmoins, le segment de subduction au nord du Pérou (de lat.3oS à 9oS) est resté le seul segment sismiquement silencieux depuis les premières informations historiques sur les séismes qui remontent au XVème siècle. Avant les travaux présentés dans ce manuscrit, aucune information sur les processus accommodant la convergence de la plaque Nazca vers le continent Sud-Américain n’était disponible le long du segment de 1000km au nord Pérou et sud Equateur. Les techniques de géodésie spatiale, en particulier le GPS/GNSS, nous permettent de quantifier les mouvements à la surface de la plaque supérieure avec une précision millimétrique. Ces mesures, couplées à l'utilisation de modèles élastiques, nous permettent de déterminer le niveau du couplage intersismique le long de l'interface entre les plaques. Le but de ma thèse est d'étudier le cycle sismique et la déformation continentale le long de la zone de subduction du Pérou, avec un intérêt particulier pour son segment nord. Nous utilisons des mesures GPS acquises depuis 2008 dans le cadre d'un projet international (le projet Andes Du Nord, ANR- ADN). Le champ de vitesse GPS obtenu couvre l’ensemble de la marge de subduction péruvienne, avec des mesures dans la cordillère et dans une moindre mesure dans la région sub-Andine. L'analyse et la modélisation du champ de vitesse GPS ont permis d'obtenir les résultats suivants: Premièrement: nous mettons en évidence l'existence d'un nouveau domaine continental, que nous avons baptisé comme le sliver Inca et qui est en translation a une vitesse de 4-5 mm/an en direction sud-est par rapport au craton Sud Américain. Le sliver Inca s’étend tout le long de la marge péruvienne.The Nazca/South American subduction zone is one of the most active regions on Earth. Large earthquakes and associated tsunamis occur recurrently almost all along its margin. Nevertheless, the ~1000 km long (from lat.2oS to 9oS) segment in northern Peru and southern Ecuador subduction has remained in relative seismic silence for at least the past five centuries. Before the work presented in this thesis, no information about the processes accommodating the convergence was available for this region and it was impossible to answer whether it could host a great Mw>8.5 earthquake in future or not. Nowadays, spatial geodesy, and more specifically GPS/GNSS enable us to quantify the surface displacement on the overriding plate with millimeter accuracy. Geodetic measurements together with the use of elastic models allow us to determine the amount of interseismic coupling at the plate interface. My thesis focuses on the seismic cycle and the continental deformation along the Peruvian subduction margin, with particular interest along its northern and central segments. We use GPS measurements acquired since 2008 in the frame of an international French-Peruvian- Ecuadorian project (the Andes Du Nord project, ADN). Our GPS velocity field covers the entire Peruvian subduction margin, with measurements in the Andean cordillera and part of the sub-Andean region. Modeling of GPS velocity field show the existence of a new tectonic microplate that we baptized as the Inca Sliver, which is in southeastward translation a rate of 4-5 mm/yr with respect to stable South America