Abstract
We would like to test the concept that induced seismicity prior to relatively large mining tremor (ML > 2.5, E > 106J) 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 ML 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.
Highlights
Accelerating energy release (AER), accelerating moment release (AMR) or Benioff strain release (BSR) represent the critical-point-like models of natural earthquakes
The process of AER/AMR/ BSR for natural earthquakes has to fulfil two criteria for the precursory sequence: (1) the record of events is complete for an appropriate time interval preceding the main shock, where a complete record must contain all events within approximately two magnitudes of the mainshock magnitude; (2) there are no interfering events which are events that occur within the same time period and location, and have similar or greater magnitudes (Brehm and Braile 1998)
The BSR function was calculated (Fig. 8) and it produced m-parameter varying in the range of 0.304–0.542 indicating that the entire study area is characterised by an accelerating-like sequence of induced seismicity
Summary
Accelerating energy release (AER), accelerating moment release (AMR) or Benioff strain release (BSR) represent the critical-point-like models of natural earthquakes. Authors have studied the spatial changes of AER/ AMR/BSR according to the range of the searching radius, indicating whether the process of acceleration occurred or not in the vicinity of the target tremor focus (e.g.: Bowman et al 1998; Jiang and Wu 2006; and works cited there), and statistical tests were introduced to assess the intermediate-term prediction of a strong event The process of AER/AMR/ BSR for natural earthquakes has to fulfil two criteria for the precursory sequence: (1) the record of events is complete for an appropriate time interval preceding the main shock, where a complete record must contain all events within approximately two magnitudes of the mainshock magnitude (i.e., it has a linear magnitude–frequency relationship); (2) there are no interfering events which are events that occur within the same time period and location, and have similar or greater magnitudes (generally within one magnitude unit) (Brehm and Braile 1998). The choice of the strongest event was dictated by the individual statistics of each catalogue and the ranges of data that were chosen arbitrarily to meet the criterion of completeness and the absence of interfering events
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