Atypical evolution of seismicity patterns resulting from the coupled natural, human-induced and coseismic stresses in a longwall coal mining environment

Kozlowska, Maria and Orlecka-Sikora, Beata and Rudzinski, Lukasz and Cielesta, Szymon and Mutke, Grzegorz (2016) Atypical evolution of seismicity patterns resulting from the coupled natural, human-induced and coseismic stresses in a longwall coal mining environment. International Journal of Rock Mechanics and Mining Sciences, 86. pp. 5-15. DOI: https://doi.org/10.1016/j.ijrmms.2016.03.024

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Official URL: http://doi.org/10.1016/j.ijrmms.2016.03.024

Abstract

A very unusual time-space distribution of seismicity accompanying coal exploitation has been observed in a Polish mine. The earthquakes did not follow the depth of mining but exhibited changing depths from far below to close to the mined seam. One of the deep events which occurred at close epicentral distance to the active mining front was ML3.7 event. This paper presents the study of possible coupling of natural, human-induced and coseismic stresses in a longwall coal mining environment. The full moment tensor solution showed that the strong earthquake occurred on an almost vertical plane consistent with approximate strike of local tectonic structure. The signal correlation analysis revealed some highly correlated pairs within both deep and shallow event groups. To evaluate inducing factor of ongoing and past exploitation, geomechanical modelling of its influence on strain and stress at the target depth has been performed. The results exhibited a changing vertical stress regime, which might have promoted failure on preexisting, almost vertical planes of weakness. The earthquakes' rate variation in time showed no increase in activity right after the occurrence of ML3.7 event. The P-S-wave spectra corner frequency ratio had an average of 1.0, suggesting slow rupture. However, the Coulomb stress change analysis showed that the magnitude of stress changes due to coseismic slip of ML3.7 event at the hypocentral depth is of the same order as the stress changes caused by mining. Thus, the distribution of seismicity at this level could have been driven by both exploitation and coseismic stresses. Moreover, the seismicity which occurred within first few weeks after ML3.7 event, followed positive stress changes. All the obtained results let us prove that the ML3.7 event was a tectonic earthquake triggered by ongoing exploitation and that the distribution of following seismicity was affected by coupled natural, exploitation-induced and coseismic stresses.

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Item Type: Article
Uncontrolled Keywords: Mining induced seismicity; Coulomb stress transfer; Tectonic stress
Subjects: Methodology > Method and procesing > Collective properties of seismicity
Methodology > Method and procesing > Technology-seismicity interaction
Methodology > Method and procesing > Stress field modeling
Region > Poland > Upper Silesia
Inducing technology > Underground mining
Project: IS-EPOS project > BOBREK MINE: Seismicity linked to longwall mining
EPOS-IP > BOBREK MINE: Seismicity linked to longwall mining