Joint Inversion of Coseismic and Early Postseismic Slip to Optimize the Information Content in Geodetic Data: Application to the 2009 M_w 6.3 L'Aquila Earthquake, Central Italy

When analyzing the rupture of a large earthquake, geodetic data are often critical. These data are generally characterized by either a good temporal or a good spatial resolution, but rarely both. As a consequence, many studies analyze the coseismic rupture with data that also include one or more days of early postseismic deformation. Here, we invert simultaneously for the coseismic and postseismic slip with the condition that the sum of the two models remains compatible with data covering the two slip episodes. We validate the benefits of this approach with a toy model and an application to the 2009 M_w 6.3 L'Aquila earthquake, using a Bayesian approach and accounting for epistemic uncertainties. For the L'Aquila earthquake, we find that if early postseismic deformation is not an explicitly acknowledged coseismic signal, coseismic slip models may overestimate the peak amplitude while long‐term postseismic models may largely underestimate the total postseismic slip amplitude. This example illustrates how the proposed approach could improve our comprehension of the seismic cycle, fault frictional properties, and the spatial and temporal relationship between seismic rupture, afterslip, and aftershocks

Caractérisation de la source des séismes par inversion des données sismologiques et géodésiques : mécanismes au foyer, optimisation des modèles de vitesse, distribution du glissement cosismique

Studies of the earthquake source are based on observations of seismic ground motions. They also depend on the quality and the density of measurements. In this present work we will present studies of the determination of focal mechanism of main aftershocks of the Les Saintes (MW 6.4, 2004) earthquake, and the determination of the coseismic slip of the L’Aquila (MW 6.3, 2009), the Miyagi-Oki (MW 7.2, 2005), ant the Sanriku-Oki (MW 7.3, 2011) earthquakes. These studies were based on two inversion methods. Different kinds of data were available (strong motion, broadband teleseismic, GPS and InSAR) depending on the earthquake studied. But the multiplicity of data is not sufficient to well describe rupture process. There are others difficulties as the data modeling of strong motion. Seismic velocity models are used to describe the characteristics of layers crossed by seismic waves. The quality of the modeling is depending on the pertinence of these seismic velocity models. The description of the rupture process is also depending on the non-uniqueness of the best solution given by global inversion methods. We propose two procedures in order to take into account these two classic issues. First, we developed a velocity model exploration procedure to obtain optimized 1D velocity models in order to improve the strong motion modeling of the L’Aquila earthquake. Then we developed a procedure to build an average rupture model from the combined results of several joint inversions, which was applied to the L’Aquila, the Miyagi-Oki, and the Sanriku-Oki earthquake. This thesis presents all these works and answers to the raised issues.La caractérisation de la source d’un séisme se fait à partir de l’analyse des mesures des déplacements transitoires et statiques du sol, et dépend de la quantité et de la qualité de ces mesures. Nous avons travaillé sur la détermination des mécanismes au foyer des répliques du séisme de Saintes (MW 6.4, 2004), et sur la détermination de la distribution spatio-temporelle du glissement cosismique des séismes de L’Aquila (Mw 6.3, 2009), et de Miyagi-Oki (Mw 7.2, 2005) et de Sanriku-Oki (Mw 7.3, 2011). Ces travaux se sont basés sur des méthodes d’inversions, et différents jeux de données (accélérométriques, large-bandes, GPS et InSAR) accessibles ou non selon le séisme considéré. La seule diversité des mesures n’est pas suffisante pour décrire la rupture. La modélisation des données se confronte à des difficultés, comme par exemple la pertinence des modèles de vitesses sismiques pour la modélisation des données accélérométriques. Une autre problématique récurrente est la non-unicité de la meilleure solution déterminée par les méthodes d’inversions pour décrire les données. Pour répondre à ces deux problématiques, nous avons d‘une part développé une procédure d’exploration de modèles de vitesse pour déterminer les valeurs optimales capables de décrire au mieux les données accélérométriques du séisme de L’Aquila. D’autre part, nous avons développé une procédure de construction d’un modèle de source moyen que nous avons appliqué pour la détermination du glissement cosismique des séismes de L’Aquila, de Miyagi-Oki, et de Sanriku-Oki. L’ensemble de ces travaux et les réponses aux problèmes soulevés sont présentés dans ce travail de thèse

Characterization of the seismic source by inversion of seismological and geodetic data : focal mechanisms, optimization of velocity models, coseismic slip distribution

La caractérisation de la source d’un séisme se fait à partir de l’analyse des mesures des déplacements transitoires et statiques du sol, et dépend de la quantité et de la qualité de ces mesures. Nous avons travaillé sur la détermination des mécanismes au foyer des répliques du séisme de Saintes (MW 6.4, 2004), et sur la détermination de la distribution spatio-temporelle du glissement cosismique des séismes de L’Aquila (Mw 6.3, 2009), et de Miyagi-Oki (Mw 7.2, 2005) et de Sanriku-Oki (Mw 7.3, 2011). Ces travaux se sont basés sur des méthodes d’inversions, et différents jeux de données (accélérométriques, large-bandes, GPS et InSAR) accessibles ou non selon le séisme considéré. La seule diversité des mesures n’est pas suffisante pour décrire la rupture. La modélisation des données se confronte à des difficultés, comme par exemple la pertinence des modèles de vitesses sismiques pour la modélisation des données accélérométriques. Une autre problématique récurrente est la non-unicité de la meilleure solution déterminée par les méthodes d’inversions pour décrire les données. Pour répondre à ces deux problématiques, nous avons d‘une part développé une procédure d’exploration de modèles de vitesse pour déterminer les valeurs optimales capables de décrire au mieux les données accélérométriques du séisme de L’Aquila. D’autre part, nous avons développé une procédure de construction d’un modèle de source moyen que nous avons appliqué pour la détermination du glissement cosismique des séismes de L’Aquila, de Miyagi-Oki, et de Sanriku-Oki. L’ensemble de ces travaux et les réponses aux problèmes soulevés sont présentés dans ce travail de thèse.Studies of the earthquake source are based on observations of seismic ground motions. They also depend on the quality and the density of measurements. In this present work we will present studies of the determination of focal mechanism of main aftershocks of the Les Saintes (MW 6.4, 2004) earthquake, and the determination of the coseismic slip of the L’Aquila (MW 6.3, 2009), the Miyagi-Oki (MW 7.2, 2005), ant the Sanriku-Oki (MW 7.3, 2011) earthquakes. These studies were based on two inversion methods. Different kinds of data were available (strong motion, broadband teleseismic, GPS and InSAR) depending on the earthquake studied. But the multiplicity of data is not sufficient to well describe rupture process. There are others difficulties as the data modeling of strong motion. Seismic velocity models are used to describe the characteristics of layers crossed by seismic waves. The quality of the modeling is depending on the pertinence of these seismic velocity models. The description of the rupture process is also depending on the non-uniqueness of the best solution given by global inversion methods. We propose two procedures in order to take into account these two classic issues. First, we developed a velocity model exploration procedure to obtain optimized 1D velocity models in order to improve the strong motion modeling of the L’Aquila earthquake. Then we developed a procedure to build an average rupture model from the combined results of several joint inversions, which was applied to the L’Aquila, the Miyagi-Oki, and the Sanriku-Oki earthquake. This thesis presents all these works and answers to the raised issues

Dix années d’éducation au risque sismique en Haïti

International audienceUne des missions de l’école est de permettre aux élèves de mieux appréhender les sciences autrefois confinées dans les laboratoires scientifiques. Depuis une vingtaine d’années, un programme de sismologie éducative a été mis sur pied en France métropolitaine puis dans les Caraïbes. Le point innovant de ce programme est de permettre à des élèves d’installer un sismomètre à vocation éducative dans leur école. Avec le séisme du 12 janvier 2010 à Port-au-Prince, ce programme éducatif s’est intensifié auprès des écoles haïtiennes et notamment au collège Catts Pressoir (http ://sismo.gpetech.net). Une nouvelle génération d’élèves et d’enseignants s’approprie aujourd’hui cette approche d’éducation au risque sismique au sein d’un même projet coopératif présent dans plusieurs écoles sur le territoire haïtien. Avec une dizaine de stations installées dans les Caraïbes, la réalisation du programme a dépassé le simple objectif de mise à disposition de signaux sismiques qu’auraient pu procurer les centres de surveillance. Par une appropriation de la mesure scientifique, l’élève s’implique et réalise l’apprentissage de notions complexes autour des géosciences. Le développement d’outils simples, la mise au point d’expériences concrètes associées à une démarche d’investigation permet de construire avec les élèves une culture scientifique de qualité et une éducation citoyenne du risque.Yonn nan misyon lekòl la se pèmèt elèv yo byen konprann lasyans ki anvan sa, te fèmen anndan laboratwa syantifik yo. Depi yon ven ane, yon pwogram sismoloji edikatif te mete kanpe sou tè prensipal Lafrans ak nan Karayib la. Pwen inovatè nan pwogram sa a se pèmèt elèv yo enstale yon sismomèt edikasyonèl nan lekòl yo. Avèk tranbleman tè 12 janvye 2010 la nan Pòtoprens, pwogram edikasyon sa a entansifye nan lekòl ayisyen yo, an patikilye nan kolèj Catts Pressoir (http://sismo.gpetech.net). Yon nouvo jenerasyon elèv ak pwofesè ap pran posesyon apwòch edikasyon risk sismik sa a nan yon sèl pwojè koperativ ki anndan plizyè lekòl an Ayiti.Avèk yon dizèn estasyon enstale nan Karayib la, realizasyon pwogram sa a depase senp objektif bay siyal sismik nou te kap jwenn nan sant siveyans yo. Lè elèv lan apwo-priye li de mezi syantifik la, li vin patisipe epi aprann konsèp konplèks alantou jeosyans. Devlopman zouti ki senp, devlopman eksperyans konkrè ki asosye ak yon apwòch envestigasyon fè li posib pou nou bati ak elèv yo yon bon kalite kilti syantifik ak yon edikasyon sitwayen sou risk

Celebrating 25 years of seismology at schools in France

International audienc

Joint Inversion of Coseismic and Early Postseismic Slip to Optimize the Information Content in Geodetic Data: Application to the 2009 M w 6.3 L'Aquila Earthquake, Central Italy

International audienceWhen analyzing the rupture of a large earthquake, geodetic data are often critical. These data are generally characterized by either a good temporal or a good spatial resolution, but rarely both. As a consequence, many studies analyze the coseismic rupture with data that also include one or more days of early postseismic deformation. Here, we invert simultaneously for the coseismic and postseismic slip with the condition that the sum of the two models remains compatible with data covering the two slip episodes. We validate the benefits of this approach with a toy model and an application to the 2009 Mw6.3 L'Aquila earthquake, using a Bayesian approach and accounting for epistemic uncertainties. For the L'Aquila earthquake, we find that if early postseismic deformation is not an explicitly acknowledged coseismic signal, coseismic slip models may overestimate the peak amplitude while long‐term postseismic models may largely underestimate the total postseismic slip amplitude. This example illustrates how the proposed approach could improve our comprehension of the seismic cycle, fault frictional properties, and the spatial and temporal relationship between seismic rupture, afterslip, and aftershocks

The InSight Blind Test: An Opportunity to Bring a Research Dataset into Teaching Programs

International audienceOn November 26, 2019, SEIS, the first broadband seismometer designed for the Martian environment (Lognonné et al., 2019) landed on Mars thanks to NASA’s InSight mission. On April 6, 2019 (sol 128), the InSight Science team detected the first historical “marsquake” (NASA news release). Before it was recorded, the InSight Science team developed the InSight Blind Test (hereafter IBT), which consists of a 12-month period of continuous waveform data combining realistic estimates of martian background seismic noise, 204 tectonic and 35 impact events (Clinton et al., 2017). This project was originally designed to prepare scientists for the arrival of real data from the upcoming InSight mission. This paper presents the work carried out by middle and high school students during this challenge. This project offered schools the opportunity to participate in and strengthen the link between secondary schools and universities. The IBT organizers accepted the approach to enable fourteen schools to take part in this scientific challenge. After a training process, each school analyzed the IBT dataset to contribute to the collaborative School Team catalog. The schools relied on a manual procedure combining analyses in time and frequency domains. At the end, a combined catalog was submitted as one of the IBT entries. The IBT organizers then assessed the catalog submitted by the consortium of schools together with the results from science teams (Van Driel et al., 2019). The schools achieved a total of 15 correct detections over a short time period. While this number may seem modest compared with the 239 synthetic marsquakes included in the IBT waveform data, these correct detections were entirely made during class time. All in all, the students seemed to be fully engaged, and this exercise seemed to increase their scientific inquiry skills in order to fulfill their task as a team

Early Endothelial Dysfunction in Type 1 Diabetes Is Accompanied by an Impairment of Vascular Smooth Muscle Function: A Meta-Analysis.

Background: A large yet heterogeneous body of literature exists suggesting that endothelial dysfunction appears early in type 1 diabetes, due to hyperglycemia-induced oxidative stress. The latter may also affect vascular smooth muscles (VSM) function, a layer albeit less frequently considered in that pathology. This meta-analysis aims at evaluating the extent, and the contributing risk factors, of early endothelial dysfunction, and of the possible concomitant VSM dysfunction, in type 1 diabetes.Methods: PubMed, Web of Sciences, Cochrane Library databases were screened from their respective inceptions until October 2019. We included studies comparing vasodilatory capacity depending or not on endothelium (i.e., endothelial function or VSM function, respectively) in patients with uncomplicated type 1 diabetes and healthy controls.Results: Fifty-eight articles studying endothelium-dependent function, among which 21 studies also assessed VSM, were included. Global analyses revealed an impairment of standardized mean difference (SMD) (Cohen's d) of endothelial function: −0.61 (95% CI: −0.79, −0.44) but also of VSM SMD: −0.32 (95% CI: −0.57, −0.07). The type of stimuli used (i.e., exercise, occlusion-reperfusion, pharmacological substances, heat) did not influence the impairment of the vasodilatory capacity. Endothelial dysfunction appeared more pronounced within macrovascular than microvascular beds. The latter was particularly altered in cases of poor glycemic control [HbA1c > 67 mmol/mol (8.3%)].Conclusions: This meta-analysis not only corroborates the presence of an early impairment of endothelial function, even in response to physiological stimuli like exercise, but also highlights a VSM dysfunction in children and adults with type 1 diabetes. Endothelial dysfunction seems to be more pronounced in large than small vessels, fostering the debate on their relative temporal appearance

Le réseau de sismologie citoyenne en Haïti face au séisme de Nippes (Mw 7.2) du 14 Aout 2021

International audienceLe 14 Aout 2021, un séisme de magnitude 7.2 frappe le sud d'Haiti, cause la mort de 2500 personnes et la destruction de 53000 maisons. Ce séisme et ses répliques sont bien enregistrés par le réseau sismo-citoyen installé depuis 2019 en Haiti. Les données nous permettent de caractériser le choc principal (PGA de 0.32 g mesuré à 21 km) et de suivre en temps réel l'évolution des répliques (http://ayiti.unice.fr/ayiti-seismes/). La faille a joué sur environ 50km de long avec un mouvement oblique majoritairement compressif à l'est et décrochant à l'ouest.Le réseau sismo-citoyen est actuellement constitué de 15 stations sismologiques à bas coût (Raspberry shake) installées chez des citoyens haïtiens volontaires (données ouvertes).Dans le projet OSMOSE (ANR 2022-2026, PI E. Calais), nous proposons d'étendre ce réseau, de diversifier les hébergeurs (particuliers, écoles, entreprises ...), et de mener un travail interdisciplinaire approfondi entre sociologues et sismologues Haïtiens et Français (Cadre LMI CARIBACT de l'IRD)

A Socio-Seismology Experiment in Haiti

International audienceEarthquake risk reduction approaches classically apply a top-down model where scientific information is processed to deliver risk mitigation measures and policies understandable by all, while shielding end-users from the initial, possibly complex, information. Alternative community-based models exist but are rarely applied at a large scale and rely on valuable, but non-scientific, observations and experiences of local populations. In spite of risk reduction efforts based on both approaches, changes in behaviour or policies to reduce earthquake risk are slow or even non-existent, in particular in developing countries. Here we report on the initial stage of a project that aims at testing, through a participatory seismology experiment in Haiti—a country struck by a devastating earthquake in January 2010—whether public or community involvement through the production and usage of seismic information can improve earthquake awareness and, perhaps, induce grassroots protection initiatives. This experiment is made possible by the recent launch of very low-cost, plug-and-play, Raspberry Shake seismological stations, the relative ease of access to the internet even in developing countries such as Haiti, and the familiarity of all with social networks as a way to disseminate information. Our early findings indicate that 1) the seismic data collected is of sufficient quality for real-time detection and characterization of the regional seismicity, 2) citizens are in demand of earthquake information and trust scientists, even though they appear to see earthquakes through the double lens of tectonics and magic/religion, 3) the motivation of seismic station hosts has allowed data to flow without interruption for more than a year, including through a major political crisis in the Fall of 2019 and the current COVID19 situation. At this early stage of the project, our observations indicate that citizen-seismology in a development context has potential to engage the public while collecting scientifically-relevant seismological informatio