Non-stationarity and internal correlations of the occurrence process of mining-induced seismic events

A point process, e.g., the seismic process, is potentially predictable when it is non-stationary, internally correlated or both. In this paper, an analysis of the occurrence process of mining-induced seismic events from Rudna copper mine in Poland is presented. Stationarity and internal correlation are investigated in complete seismic time series and segmentally in subseries demonstrating relatively stable seismicity rates. It is shown that the complete seismic series are non-stationary; however, most of their shorter subseries become stationary. In the stationary subseries, the distribution of interevent time is closer to the exponential distribution, which is characteristic for the Poisson process. However, in most of these subseries, the differences between the interevent time and Poisson distributions are still significant, revealing correlations among seismic events

Significance of static stress transfer caused by coseismic slip of mining-induced seismic events in seismicity generation process in mines

We investigated an effect of static stress transfer for the mining-induced seismicity from Rudna Mine. We consider events of energy over 10/5J, which occurred in Rudna Mine from 1993-2006. We examine the possible triggering checking correlation between event locations and the stress-increased zones. We find that more than 50% of the analyzed seismic events occurred in areas where stress was enhanced due to the occurrence of previous events. Statistical test proved that for stress changes from 0.02 bar static stress triggering in Rudna Mine exists and this effect is statistically significant at the 95% confidence level

Forecasting seismicity rates in western Turkey as inferred from earthquake catalog and stressing history

The spatio-temporal variation in seismicity in western Turkey since the late 1970s is investigated through a rate/state model, which considers the stressing history to forecast the reference seismicity rate evolution. The basic catalog was divided according to specific criteria into four subsets, which correspond to areas exhibiting almost identical seismotectonic features. Completeness magnitude and reference seismicity rates are individually calculated for each subset. The forecasting periods are selected to be the inter-seismic time intervals between successive strong (M ≥ 5.8) earthquakes. The Coulomb stress changes associated with their coseismic slip are considered, along with the constant stressing rate to alter the rates of earthquake production. These rates are expressed by a probability density function and smoothed over the study area with different degrees of smoothing. The influence of the rate/state parameters in the model efficiency is explored by evaluating the Pearson linear correlation coefficient between simulated and observed earthquake occurrence rates along with its 95 % confidence limits. Application of different parameter values is attempted for the sensitivity of the calculated seismicity rates and their fit to the real data to be tested. Despite the ambiguities and the difficulties involved in the experimental parameter value determination, the results demonstrate that the present formulation and the available datasets are sufficient enough to contribute to seismic hazard assessment starting from a point such far back in time

Seismicity rate changes in association with the evolution of the stress field in northern Aegean Sea, Greece

Seismicity rate changes in northern Aegean area were studied by applying the Dieterich (1994) Rate/State formulation. The study area was divided into four smaller ones that exhibit seismotectonic homogeneity and accommodate strong events with similar to identical focal mechanisms. Seismicity rate evaluation concerns the ‘study period’ between 1981 December 19 and 2010 August 31, whereas the reference seismicity rate was estimated for the ‘learning period’ lasting from 1970 January 1 to 1981 December 19. The coseismic slip of the strongest events (Mw ≥ 5.8) that occurred during the study period was considered to contribute to the stress field evolution along with the continuous tectonic loading. Stress changes were calculated just before and after each strong event and their influence was then examined in connection with the occurrence rate of the smaller magnitude events above the individually determined magnitude of completeness in each subarea and for the respective time intervals. After defining the probability density function of seismicity distribution, a Rate/State model was used to combine static Coulomb stress changes (ΔCFF) with seismicity rates and to compare the observed with the expected rates of earthquake production for each time period and subarea. Different parameter values combinations were tested to evaluate the model sensitivity. Qualitative and quantitative correlations were performed for each one of the selected study periods. The modelling approach resulted to satisfactory correlation between real and synthetic seismicity rates and is expected to constitute a useful mean for the time-dependent seismic hazard assessment