Stress transfer among en echelon and opposing thrusts and tear faults : triggering caused by the 2003 Mw = 6.9 Zemmouri, Algeria, earthquake

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): B03305, doi:10.1029/2010JB007654.The essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated, first through idealized examples and then by study of thrust faulting in Algeria. We calculated coseismic stress changes caused by the 2003 Mw = 6.9 Zemmouri earthquake, finding that a large majority of the Zemmouri afterslip sites were brought several bars closer to Coulomb failure by the coseismic stresses, while the majority of aftershock nodal planes were brought closer to failure by an average of ∼2 bars. Further, we calculated that the shallow portions of the adjacent Thenia tear fault, which sustained ∼0.25 m slip, were brought >2 bars closer to failure. We calculated that the Coulomb stress increased by 1.5 bars on the deeper portions of the adjacent Boumerdes thrust, which lies just 10–20 km from the city of Algiers; both the Boumerdes and Thenia faults were illuminated by aftershocks. Over the next 6 years, the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity. The stress also increased by 0.4 bar on the east Sahel thrust fault west of the Zemmouri rupture. Algiers suffered large damaging earthquakes in A.D. 1365 and 1716 and is today home to 3 million people. If these shocks occurred on the east Sahel fault and if it has a ∼2 mm/yr tectonic loading rate, then enough loading has accumulated to produce a Mw = 6.6–6.9 shock today. Thus, these potentially lethal faults need better understanding of their slip rate and earthquake history.Funding by the U.S. Office of Foreign Disaster Assistance of the U.S. Agency for International Development is gratefully acknowledged. Additional funding was provided by the INSU research project ACI Cat‐Nat Risque Sismique de la Région d’Alger. S. Belabbes was supported by the Algerian Ministry of Higher Education and Research

InSAR and active deformation of the Tell Atlas (Algeria) and Rif (Morocco),characterizing blind and hidden seismogenic faults along the Africa-Eurasia plate boundary

Le but de cette thèse est l'étude de la déformation crustale générée par les séismes forts et modérés dans les domaines géologiques de l'Atlas Tellien (Nord de l'Algérie) et du Rif (Nord du Maroc). Les travaux entrepris impliquent l'identification et la caractérisation des failles actives en utilisant notamment la méthode de l'Interférométrie Radar à Ouverture Synthétique (InSAR) couplée par l'analyse sismotectonique des zones actives. La déformation active en Afrique du Nord est concentrée essentiellement le long de la limite des plaques où les séismes forts à modérés sont dus à la convergence de la plaque Afrique vers l'Eurasie.La déformation de surface induite par ces séismes est souvent difficilement observable sur le terrain particulièrement dans le cas des séismes à magnitudes modérées associés à des failles aveugles (séisme d'El Hoceima, 2004 Mw 6.4, séisme d'Ain Temouchent 1999, Mw 5.7) ou dans le cas des failles cachées en mer (séisme de Zemmouri, 2003). L'application de l'InSAR aux zones tectoniques complexes où les ruptures cosismiques sont difficilement visibles, permet d'obtenir le champ de déplacement à une échelle centimétrique et de déduire les paramètres de la rupture. Par ailleurs, il est également possible d'évaluer les limites de l'application de cette méthode aux séismes à magnitudes modérées liés à différents domaines tectoniques (en compression, en extension et en décrochement). Les données SAR utilisées sont celles des satellites européens ERS-1, ERS-2 et ENVISAT ainsi que le satellite canadien RADARSAT.This thesis aims at the study of crustal deformation caused by moderate and large earthquakes in the Tell Atlas(northern Algeria) and the Rif Mountains (northern Morocco). My work included mainly the identification and characterisation of active faulting using the method of Synthetic Aperture Radar interferometry (InSAR). The active deformation and related seismicity is essentially concentrated along the Africa Eurasia plate boundary where large and moderate earthquakes result from the plate convergence. The surface deformation associated with moderate-size earthquakes is, however, very often hardly visible in the field because because the deformation occur on blind faults (e.g., El Hoceima 2004, Mw 6.4; Ain Temouchent 1999, Mw 5.7) or to hidden faults beneath Quaternary deposits or offshore along the Mediterranean coastline (e.g., Zemmouri 2003; Mw 6.8). The InSAR application to these complex tectonic zones provides an opportunity to obtain the surface field displacement (to the cm scale) and related seismic rupture parameters. In this thesis, made of five chapters I used the SAR data of ERS-1, ERS-2 and ENVISAT European satellites, as well as the data of RADARSAT Canadian satellite..

InSAR and active deformation of the Tell Atlas (Algeria) and Rif (Morocco),characterizing blind and hidden seismogenic faults along the Africa-Eurasia plate boundary

Le but de cette thèse est l'étude de la déformation crustale générée par les séismes forts et modérés dans les domaines géologiques de l'Atlas Tellien (Nord de l'Algérie) et du Rif (Nord du Maroc). Les travaux entrepris impliquent l'identification et la cThis thesis aims at the study of crustal deformation caused by moderate and large earthquakes in the Tell Atlas(northern Algeria) and the Rif Mountains (northern Morocco). My work included mainly the identification and characterisation of active faultin

Caractérisation de la déformation active par l interférométrie Radar (InSAR) (Failles sismiques aveugles et cachées de l Atlas Tellien (Algérie) et du Rif (Maroc) le long de la limite des plaques Afrique-Eurasie)

Le but de cette thèse est l étude de la déformation crustale générée par les séismes forts et modérés dans les domaines géologiques de l Atlas Tellien (Nord de l Algérie) et du Rif (Nord du Maroc). Les travaux entrepris impliquent l identification et la caractérisation des failles actives en utilisant notamment la méthode de l Interférométrie Radar à Ouverture Synthétique (InSAR) couplée par l analyse sismotectonique des zones actives. La déformation active en Afrique du Nord est concentrée essentiellement le long de la limite des plaques où les séismes forts à modérés sont dus à la convergence de la plaque Afrique vers l Eurasie.La déformation de surface induite par ces séismes est souvent difficilement observable sur le terrain particulièrement dans le cas des séismes à magnitudes modérées associés à des failles aveugles (séisme d El Hoceima, 2004 Mw 6.4, séisme d Ain Temouchent 1999, Mw 5.7) ou dans le cas des failles cachées en mer (séisme de Zemmouri, 2003). L application de l InSAR aux zones tectoniques complexes où les ruptures cosismiques sont difficilement visibles, permet d obtenir le champ de déplacement à une échelle centimétrique et de déduire les paramètres de la rupture. Par ailleurs, il est également possible d évaluer les limites de l application de cette méthode aux séismes à magnitudes modérées liés à différents domaines tectoniques (en compression, en extension et en décrochement). Les données SAR utilisées sont celles des satellites européens ERS-1, ERS-2 et ENVISAT ainsi que le satellite canadien RADARSAT.This thesis aims at the study of crustal deformation caused by moderate and large earthquakes in the Tell Atlas(northern Algeria) and the Rif Mountains (northern Morocco). My work included mainly the identification and characterisation of active faulting using the method of Synthetic Aperture Radar interferometry (InSAR). The active deformation and related seismicity is essentially concentrated along the Africa Eurasia plate boundary where large and moderate earthquakes result from the plate convergence. The surface deformation associated with moderate-size earthquakes is, however, very often hardly visible in the field because because the deformation occur on blind faults (e.g., El Hoceima 2004, Mw 6.4; Ain Temouchent 1999, Mw 5.7) or to hidden faults beneath Quaternary deposits or offshore along the Mediterranean coastline (e.g., Zemmouri 2003; Mw 6.8). The InSAR application to these complex tectonic zones provides an opportunity to obtain the surface field displacement (to the cm scale) and related seismic rupture parameters. In this thesis, made of five chapters I used the SAR data of ERS-1, ERS-2 and ENVISAT European satellites, as well as the data of RADARSAT Canadian satellite...STRASBOURG-EOST (674822249) / SudocSudocFranceF

Fully Convolutional Neural Network for Rapid Flood Segmentation in Synthetic Aperture Radar Imagery

Rapid response to natural hazards, such as floods, is essential to mitigate loss of life and the reduction of suffering. For emergency response teams, access to timely and accurate data is essential. Satellite imagery offers a rich source of information which can be analysed to help determine regions affected by a disaster. Much remote sensing flood analysis is semi-automated, with time consuming manual components requiring hours to complete. In this study, we present a fully automated approach to the rapid flood mapping currently carried out by many non-governmental, national and international organisations. We design a Convolutional Neural Network (CNN) based method which isolates the flooded pixels in freely available Copernicus Sentinel-1 Synthetic Aperture Radar (SAR) imagery, requiring no optical bands and minimal pre-processing. We test a variety of CNN architectures and train our models on flood masks generated using a combination of classical semi-automated techniques and extensive manual cleaning and visual inspection. Our methodology reduces the time required to develop a flood map by 80%, while achieving strong performance over a wide range of locations and environmental conditions. Given the open-source data and the minimal image cleaning required, this methodology can also be integrated into end-to-end pipelines for more timely and continuous flood monitoring

Effects of pre-operative isolation on postoperative pulmonary complications after elective surgery: an international prospective cohort study an international prospective cohort study

We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05–1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4–7 days or ≥ 8 days of 1.25 (1.04–1.48), p = 0.015 and 1.31 (1.11–1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care. We aimed to determine the impact of pre-operative isolation on postoperative pulmonary complications after elective surgery during the global SARS-CoV-2 pandemic. We performed an international prospective cohort study including patients undergoing elective surgery in October 2020. Isolation was defined as the period before surgery during which patients did not leave their house or receive visitors from outside their household. The primary outcome was postoperative pulmonary complications, adjusted in multivariable models for measured confounders. Pre-defined sub-group analyses were performed for the primary outcome. A total of 96,454 patients from 114 countries were included and overall, 26,948 (27.9%) patients isolated before surgery. Postoperative pulmonary complications were recorded in 1947 (2.0%) patients of which 227 (11.7%) were associated with SARS-CoV-2 infection. Patients who isolated pre-operatively were older, had more respiratory comorbidities and were more commonly from areas of high SARS-CoV-2 incidence and high-income countries. Although the overall rates of postoperative pulmonary complications were similar in those that isolated and those that did not (2.1% vs 2.0%, respectively), isolation was associated with higher rates of postoperative pulmonary complications after adjustment (adjusted OR 1.20, 95%CI 1.05–1.36, p = 0.005). Sensitivity analyses revealed no further differences when patients were categorised by: pre-operative testing; use of COVID-19-free pathways; or community SARS-CoV-2 prevalence. The rate of postoperative pulmonary complications increased with periods of isolation longer than 3 days, with an OR (95%CI) at 4–7 days or ≥ 8 days of 1.25 (1.04–1.48), p = 0.015 and 1.31 (1.11–1.55), p = 0.001, respectively. Isolation before elective surgery might be associated with a small but clinically important increased risk of postoperative pulmonary complications. Longer periods of isolation showed no reduction in the risk of postoperative pulmonary complications. These findings have significant implications for global provision of elective surgical care