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  • 1
    Deutsches GeoForschungsZentrum GFZ
    In:  System Erde
    Publication Date: 2019-06-13
    Description: Sinkholes are circular to elliptical depression or collapse structures in the Earth?s surface, caused by dissolution and subsurface erosion of soluble rocks such as salt, sulfate and carbonate in the presence of groundwater. Depending on the subsoil structure and generation process, sinkholes may form continuously growing depressions at the surface or collapse abruptly into deep holes with diameters up to several tens of meters. Individual process components may be simple and can easily be understood, but the interaction of different processes ahead of a collapse and precursor phenomena with different rates and dimensions impede full process understanding. The joint project SIMULTAN develops and applies an early recognition system of sinkhole instability, unrest, and collapse, with combining structural, geodetic, geophysical, petrophysical, and hydrogeological mapping methods, accompanied by sensor development, multi-scale monitoring, modelling, and an information platform. Sinkhole-affected areas in Germany are based generally on salt highs (e.g., northern Germany), sulfate karst or carbonate karst (mainly southern Germany). The investigations focus in two areas (Hamburg, Thuringia), for which sinkhole unrest has been identified. While local authorities provide individual information and maps about areas of potential sinkhole hazard, a standardized and collective recognition system does not exist, relevant for especially urbanized areas.
    Language: German
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  • 2
    Publication Date: 2016-10-05
    Description: For induced microseismicity associated with hydraulic fracturing, the frequency-magnitude distribution is typically characterized by a falloff with increasing magnitude that is significantly faster than for seismicity along active fault systems. This characteristic may arise from a break in scale invariance, possibly due to mechanical layering that typifies fine-grained sedimentary rocks in many shale gas and tight oil reservoirs. The latter would imply the presence of spatio-temporal magnitude correlations. Using three microseismic catalogs for well stimulations in widely separated locations with varying hydraulic-fracturing methods, we show that events with similar magnitudes indeed tend to cluster in space and time. In addition, we show that the inter-event time distribution can be described by a universal functional form characterized by two power-laws. One exponent can be related to the presence of inter-event triggering as in aftershock sequences and is a consequence of the Omori-Utsu law. The other one is a reflection of the intrinsic spatial variation in the microseismic response rates. Taken together, these features are indicative of non-trivial spatio-temporal clustering of induced microseismicity and, hence, of direct relevance for time-dependent seismic hazard assessment.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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