Case Studies of Seismic Energy Release Ahead of Underground Coal Mining Before Strong Tremors

Abstract

We would like to test the concept that induced seismicity prior to relatively large mining tremor (M L [ 2.5, E [ 10 6 J) can be inferred from the cumulative Benioff strain release (BSR) as power law time-to-failure before the strong event. This study presents the application of accelerating BSR prior to a large earthquake, widely used in natural seismicity, for analysis of this phenomenon in induced seismicity. The Benioff strain release is quantified as accelerated releases of cumulative (square root sum) of seismic energy in the time series. During the study, five sequences were extracted from the seismic catalogues from two Polish hard coal mines: exhausted Bobrek Mine (data form the IS-EPOS Platform) and from a mine belonging to the Polish Mining Group. Next, a search radius was used to select precursory events and to indicate the type of processes occurring in the coal seam and its vicinity. The fitted power law of cumulative Benioff strain release showed changes of m-parameter. If the value of m was lower than 1.0, the process was regarded as an accelerating-like and if m was higher than 1.0-as a quiescence-like. The investigation of m-parameter vs. the search radius showed the general behaviour of the rock mass in the studied areas and allowed to evaluate the relationship between the critical radius and magnitude of the target event. The obtained scaling relation log(Rc) * 0.35 M L is similar to these reported by other authors who analysed natural seismicity which might suggest that the scaling relation works in a wide range of magnitudes.

The influence of distant coal seam edges on seismic hazard during longwall mining

“…9a). The Benioff strain is defined as the root square of the seismic energy and presented as a cumulative plot (Mendecki et al 2019). The cumulative Benioff strain release (BSR) models enable the approximation of the behaviour of the stress regime in the rock masses surrounding longwall fields, and they can be used to better understand the processes occurring during underground exploitation (Mendecki et al 2019).…”

“…The Benioff strain is defined as the root square of the seismic energy and presented as a cumulative plot (Mendecki et al 2019). The cumulative Benioff strain release (BSR) models enable the approximation of the behaviour of the stress regime in the rock masses surrounding longwall fields, and they can be used to better understand the processes occurring during underground exploitation (Mendecki et al 2019). The BSR models (or similar using seismic moment or energy) originated from the work of Voight (1989), which describes the behaviour of materials in terminal stages of failure under conditions of approximately constant stress and temperature.…”

“…Brehm and Braile 1999;Jiang and Wu 2005;Jiang and Wu 2006). An idea that seismic energy release can be applied to the induced (or anthropogenic) seismicity was introduced by Mendecki (1996), and it is still developed. Mendecki et al (2019) suggested that mined coal seam can be treated as closed system, analogically to the Voight's sample under pressure, and the occurring rate Fig.…”

“…An idea that seismic energy release can be applied to the induced (or anthropogenic) seismicity was introduced by Mendecki (1996), and it is still developed. Mendecki et al (2019) suggested that mined coal seam can be treated as closed system, analogically to the Voight's sample under pressure, and the occurring rate Fig. 8 The seismic hazard assessment results: (a) comparison of the cumulative probability distribution function of the maximum energy (blue line) and empirical cumulative distribution (red line); (b) the probability of the occurrence of an event with energy of > 5•10 5 J per 10-day interval (red line) and the cumulated energy released during 10-day intervals; (c) the probability of the occurrence of an event with energy of > 5•10 5 J per 10-day interval (red line) and the event frequency per 10-day interval (λ) (blue line); and (d) the probability of the occurrence of an event with energy of > 5•10 5 J per 10-day interval (red line) and the 10-day moving average of energy released and size of seismic event release is governed by the same physical process.…”

“…The simplified model proposed for the rate at which the Benioff strain is released during a mining tremor sequence prior to a strong event can be presented as follow (Mendecki et al 2019):…”