O alemão em Blumenau: uma questão de identidade e cidadania

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão. Programa de Pós-Graduação em Linguística

Activité microsismique et caractérisation de la détectabilité des réseaux de surveillance du bassin houiller de Gardanne

National audienceMining in Provence have left many underground voids that may cause subsidence or collapse in areas of high population density. Microseismic monitoring networks have been deployed to prevent this risk. Here we present the post-mining microseismic records between 2008 and 2012 and the characterization of networks detectability at different scales.L'activité minière en Provence a laissé de nombreux vides souterrains qui peuvent provoquer la subsidence des terrains ou des effondrements dans des zones à forte densité de population. Pour prévenir ces risques, une surveillance microsismique a été mise en place dans les zones à fort enjeux. Ainsi depuis l'arrêt des concessions minières de Provence, l'INERIS a installé 5 réseaux de surveillance microsismique sur le bassin houiller de Gardanne qui était exploité par Charbonnages de France. Puis, le BRGM-DPSM en tant que Maître d'ouvrage délégué de l'Etat, a demandé à l'INERIS la poursuite de la surveillance microsismique

Semi-automatic detection and localization of microseismicity induced by a "salt dissolution provoked" cavity collapse

Natural underground cavities, active or abandoned mine workings, particularly when they are shallow, can provoke large scale land subsidence and collapses attended by catastrophic social-economic impacts. The potential of passive microseismic monitoring to prevent such disasters was already indicated by several studies. Nonetheless, to further improve monitoring reliability a better understanding of associated seismicity is inevitable. In this context, within a large multi-parameter research project at Cerville-Buissoncourt in Lorraine, France, the growth of a single, shallow, about 150 m diameter salt cavity created by salt dissolution mining was surveyed from 2004 until 2009 when the cavity reached its critical size and a 'controlled' collapse was initiated. During the experiment, a large microseismic data set was recorded by a triggered, high resolution geophone monitoring system. Initial processing and data inspection reveal very unusual seismic signals mainly appearing in complex swarming sequences (Mercerat et al., 2010; Contrucci et al., 2011). To resolve spatio-temporal characteristics of associated seismicity we developed an semi-automatic seismic event detection and localization algorithm adressing these abnormal signal characteritics. The detector design is based on a spectral envelope function calculated for each seismogram. By this function, coherent signals are distinguished from signals comprising rather randomly distributed frequency proportions as noise or CODA waves. First application tests demonstrated highly improved event detection results when analysing seismic events of highly varying size and duration occurring in a swarming sequence. In addition, we localized the detected seismic events using inter-station amplitude ratios as introduced by Battaglia and Aki (2003) and Taisne et al. (2011). Within this approach, hypocenter source inversion relies on the decay of seismic wave amplitudes along the source-receiver path. As a result, no troublesome a priori phase segmentation is needed and the entire data set can be processed. To calibrate the local seismic attenuation law we used ~700 seismic events with known hypocenter locations found by previous studies (Klein et al., 2011). The final optimized localization algorithm sufficienty constrained the tendency of actual hypocenter source location in the cavity region. Taken all together, our detection and localization strategy provides an appropriate first order approximation to study spatio-temporal attributes of seismicity from huge data sets associated with seismic signals of unknown or complex signature as observed for Cerville-Buissoncourt

Management of post-mining large-scale ground failures : blast swarms field experiment for calibration of permanent microseismic early-warning systems

International audienceIn France, decades of coal and iron-ore mining have left extensive underground cavities beneath or in the vicinity of urban areas. This poses an environmental challenge for society. To ensure post-mining risk management and public safety, wherever remediation is not possible, numerous real-time microseismic monitoring systems are being installed. The objective is to detect remote rock mass fracturing processes, precursory events and acceleration phases for appropriate and timely action. Although no consistent collapse has occurred in any of the monitored areas yet, single 3-D probes record many microseismic events of very low amplitude which create difficulties in the quantitative data analysis. The development of specific quantitative processing has therefore become a major issue in our research work. For that purpose, a field experiment was carried out on six of the instrumented sites. It consisted of sequences of small blasts in mine pillars which were accurately controlled in terms of the location, orientation and energy of the explosive source. The data analysis was used to calibrate parameters (velocity model, 3-D sensor orientation, etc.) for reliable 3-D localization and to develop an empirical law to estimate the source energy from the sensor energy. This work now enables us to analyze real microseismic events with a considerably better level of accuracy and to obtain enough information and confidence to discuss these data in terms of site stability

Multi-parameter monitoring of a solution mining cavity collapse : first insight of precursors

International audienceIn order to improve our understanding of the large-scale ground failure phenomena caused by old underground mining works, a solution mine was instrumented in 2004 prior to its collapse as part of the mining scheme. A permanent monitoring system was set up, including a high-resolution microseismic network linked to a surface field-displacement measurement system. The large amount of data transmitted for on-line processing provided daily insight into the evolution of the geological system. First, microseismic activity showed upward progressive failure migration throughout 2008 without any significant surface movement. Second, after two days of intensive brine extraction, a high microseismicity and energy release rate marked the failure of a thin and very rigid bed at a depth of 120 m. This failure occurred 24 hours before the final collapse; it was followed by transient brine pressure signals, and by acceleration of the surface subsidence rate, reaching 1 milt in the final phas

Evolution monitoring of a solution-mining cavern in salt : identifying and analysing early-warning signals prior to collapse

International audienceRisk management of underground cavities requires a good working knowledge of accidental phenomena like subsidence or large-scale collapse. This was the context when the opportunity was taken to instrument a large size in use saline cavern, so as to test various auscultation techniques available under controlled conditions. A microseismic monitoring network coupled to a surface measurement system was installed to improve our knowledge of the mechanisms that initiate and govern the evolution of the cavern up to its collapse. After a stationary period combined with partial depressurization tests conducted in 2005 and 2007, the cavern appears to have entered into its final evolution phase, and this probably since early 2008. This results in continuous and highly sustained microseismic activity as well as the occurrence of a number of microseismic episodes localized around the cavern roof. The localization of the microseismic events, for some of these episodes, is closely correlated to the quasi-dynamic brine pressure variations and to the evolutions of the roof depth measured at observation boreholes. The microseismic activity turns out to be more precise when it comes to the evolution affecting the mine cavern than the movement measurements taken on the surface or sub-surface