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1

Temporal response of magnitude distribution to fluid injection rates in The Geysers geothermal field

Leptokaropoulos Konstantinos, Staszek Monika

Acta Geophysica

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2019

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Vol. 67, no. 1

327--339

EN

The influence of fluid injection rates on the magnitude distribution of the seismicity which occurred in the NW part of The Geysers geothermal site is studied here. A direct comparison between injection rate changes and b value response is attempted after appropriate selection of data subsets. Due to the relatively small sample (1121 events, corresponding to an average rate of ~ 0.45 events/day), we also aggregated seismic activity into two families corresponding to increasing and decreasing injection rates, respectively. The b values were calculated as a function of time lag related to the injection activity. In agreement with previous studies, we found a statistically significant direct relation between b values and injection rate changes, which occurred at a zero or very short time lag (from 0 to ~ 15 days). However, the b value changes are related to the slope (i.e., the second derivative of injection volume), instead of the absolute values of injection rates. The increasing injection rates correspond to b = 1.18 ± 0.06, whereas the decreasing injection rates correspond to b = 1.10 ± 0.05. The corresponding values estimated by the repeated medians technique are b = 1.97 ± 0.20 and b = 1.50 ± 0.13. Both differences are significant at 0.05 level.

2

Time-dependent seismic hazard in Bobrek coal mine, Poland, assuming different magnitude distribution estimations

Leptokaropoulos K., Staszek M., Cielesta Sz., Urban P., Olszewska D., Lizurek G.

Acta Geophysica

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2017

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Vol. 65, no. 3

493--505

EN

The purpose of this study is to evaluate seismic hazard parameters in connection with the evolution of mining operations and seismic activity. The time-dependent hazard parameters to be estimated are activity rate, Gutenberg–Richter b-value, mean return period and exceedance probability of a prescribed magnitude for selected time windows related with the advance of the mining front. Four magnitude distribution estimation methods are applied and the results obtained from each one are compared with each other. Those approaches are maximum likelihood using the unbounded and upper bounded Gutenberg–Richter law and the non-parametric unbounded and non-parametric upper-bounded kernel estimation of magnitude distribution. The method is applied for seismicity occurred in the longwall mining of panel 3 in coal seam 503 in Bobrek colliery in Upper Silesia Coal Basin, Poland, during 2009–2010. Applications are performed in the recently established Web-Platform for Anthropogenic Seismicity Research, available at https://tcs.ah-epos.eu/

3

Bias, variance and computational properties of Kijko’s estimators of the upper limit of magnitude distribution, Mmax

Lasocki S., Urban P.

Acta Geophysica

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2011

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Vol. 59, no. 4

657-658

EN

It is often assumed in probabilistic seismic hazard analysis that the magnitude distribution has an upper limit Mmax , which indicates a limitation on event size in specific seismogeneic conditions. Accurate estimation of Mmax from an earthquake catalog is a matter of utmost importance. We compare bias, dispersion and computational properties of four popular Mmax estimators, introduced by Kijko and others (e.g., Kijko and Sellevoll 1989, Kijko and Graham 1998, Kijko 2004) and we recommend the ones which can be the most fruitful in practical applications. We provide nomograms for evaluation of bias and standard deviation of the recommended estimators for combinations of sample sizes and distribution parameters. We suggest to use the bias nomograms to correct the Mmax estimates. The nomograms of standard deviation can be used to determine minimum sample size for a required accuracy of Mmax.