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Hidden karst structures are developed irregularly in the Middle Permian Maokou Formation aquifer from the northern part of the Guizhou coalfield, China. Mining operations associated with the exploitation of coal seams from the lower part of the Upper Permian Longtan Formation are threatened by karst waters from the underlying strata. To improve the accuracy of water inrush risk assessment of the karst aquifer floor in the northern Guizhou coalfield, the karst fractal quantification technique is implemented. In this study, the karst aquifer of the Maokou Formation located under the floor of the No. 15 coal seam from the Honglin Coal Mine is considered as the research object. Based on the karst results predicted by geophysical exploration methods, the fractal theory is used to quantify the degree of karst development, while the risk of water inrush from the floor of the coal seam is evaluated by applying ArcGIS information processing technology combined with the vulnerability index method. The results indicate the following observations: the mean fractal dimension of karst in the study area is 1.53, the karst structures are highly developed, and the overall distribution of karst is characterized by an irregular NW-SE direction; the main controlling factors affecting water inrush from the floor of the No. 15 coal seam are expressed by the water pressure of the aquifer, the abundance of water in the aquifer, the degree of karst development, the thickness of the effective impermeable layer, the mining depth, the coal seam dip angle, and the degree of fault complexity; the areas with the highest risk of floor water inrush are predominantly concentrated in the northwestern and central parts, but there is also a risk of floor water inrush in the first mining area of the No. 15 coal seam. This study takes into consideration complex factors such as the typical karst aquifer and the hydrogeological conditions in the northern part of the Guizhou coalfield, which results in a more realistic interpretation and can provide further guidance for water control activities in the mining area. [ABSTRACT FROM AUTHOR]