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European feedback on post-mining seismicity

Contrucci Isabelle, Namjesnik Dalija, Niemz Peter, Primo Paloma, Kotyrba Andrzej, Mutke Grzegorz, Konicek Petr, Dominique Pascal, Rudolph Tobias, Möllerherm Stefan, Kinscher Jannes, Klein Emmanuelle, Cesca Simone

Journal of Sustainable Mining

2023

Vol. 22. iss. 3

195--218

Following the Paris Agreement adopted in 2015, Europe has committed to reducing its greenhouse gas emissions. In this context, the abandonment of coal as an energy source, both in terms of consumption and production, will lead to the closure of many mines in the years to come. Mine closure guidelines to manage residual mining risks already exist in European countries. However, they do not include post-mining seismic risk management due to a lack of sufﬁcient studies and knowledge on this subject. After mining closure, the ﬂooding of the mining works leads to hydromechanical loading of the underground and, in the longer term, to diffusion and an increase in the pore pressure. These conditions can lead, in certain situations, to the reactivation of tectonic faults, which may cause seismic events strong enough to be felt on the surface or even produce damage. Events of lower magnitudes, usually attributed to the remobilization of old mining works, are referred to as post-mining seismic hazards. The European RFCS PostMinQuake project, which started in 2020, aims to study this hazard at ﬁve mining basins located in France, Germany, Poland and the Czech Republic, known to have experienced signiﬁcant seismicity during their operation. This analysis, based on the feedback of the partners of the project, aims to frame an inventory of the ﬁve studied mining basins, which all encounter post-mining seismicity problem today. Three basins out of ﬁve show events with local magnitudes of the order of 3-3.5, which took place between nine and thirteen years after the closure of the mines. Even though the magnitudes of these earthquakes are small to moderate, they are felt on the surface as they occur at shallow depths. In all of the considered countries, a national seismological network exists, however, none of them is fully dedicated to post-mining seismic monitoring. These networks generally consist of a sparse mesh of stations, which does not allow the detection of events of magnitude less than 1 and the location of events have high spatial uncertainties. France is not an exception, but it relies on microseismic monitoring to detect early signs of instability at the level of mining structures and to anticipate the possible appearance of surface disorders. Out of the ﬁve basins that are studied, the Gardanne basin, which has been monitored since 2008, is the most documented case study of post-mining seismicity. This article also shows the difﬁculty in identifying the key conditions and factors that can lead to the remobilization of faults.

Small-aperture array as a tool to monitor fluid injectionand extraction‑induced microseismicity: applications and recommendations

Karamzadeh Nasim, Kühn Daniela, Kriegerowski Marius, Lopez-Comino José Ángel, Cesca Simone, Dahm Torsten

Acta Geophysica

2019

Vol. 67, no. 1

311--326

The monitoring of microseismicity during temporary human activities such as fluid injections for hydrofracturing, hydrothermal stimulations or wastewater disposal is a difficult task. The seismic stations often cannot be installed on hard rock, and at quiet places, noise is strongly increased during the operation itself and the installation of sensors in deep wells is costly and often not feasible. The combination of small-aperture seismic arrays with shallow borehole sensors offers a solution. We tested this monitoring approach at two different sites: (1) accompanying a fracking experiment in sedimentary shale at 4 km depth and (2) above a gas field under depletion. The small-aperture arrays were planned according to theoretical wavenumber studies combined with simulations considering the local noise conditions. We compared array recordings with recordings available from shallow borehole sensors and give examples of detection and location performance. Although the high-frequency noise on the 50-m-deep borehole sensors was smaller compared to the surface noise before the injection experiment, the signals were highly contaminated during injection by the pumping activities. Therefore, a set of three small-aperture arrays at different azimuths was more suited to detect small events, since noise recorded on these arrays is uncorrelated with each other. Further, we developed recommendations for the adaptation of the monitoring concept to other sites experiencing induced seismicity.

SHEER “smart” database: technical note

Cielesta Szymon, Orlecka-Sikora Beata, Staszek Monika, Urban Paweł, Olszewska Dorota, Ruigrok Elmer, Toon Sam, Picozzi Matteo, Kwiatek Grzegorz, Cesca Simone, López-Comino José Angel, Isherwood Catherine, Montcoudiol Nelly, Jarosławski Janusz

Acta Geophysica

2019

Vol. 67, no. 1

291--297

The SHEER database brings together a large amount of data of various types: interdisciplinary site data from seven independent episodes, research data and those for the project results dissemination process. This concerns mainly shale gas exploitation test sites, processing procedures, results of data interpretation and recommendations. The smart SHEER database harmonizes data from different fields (geophysical, geochemical, geological, technological, etc.), creates and provides access to an advanced database of case studies of environmental impact indicators associated with shale gas exploitation and exploration, which previously did not exist. A unique component of the SHEER database comes from the monitoring activity performed during the project in one active shale gas exploration and exploitation site at Wysin, Poland, which started from the pre-operational phase. The SHEER database is capable of the adoption of new data such as results of other Work Packages and has developed an over-arching structure for higher-level integration.