Monitoring performance using synthetic data for induced microseismicity by hydrofracking at the Wysin site (Poland)

Abstract

Abstract Ideally, the performance of a dedicated seismic monitoring installation should be assessed prior to the observation of target seismicity. This work is focused on a hydrofracking experiment monitored at Wysin, NE Poland. A microseismic synthetic catalogue is generated to assess the monitoring performance during the pre-operational phase, where seismic information only concerns the noise conditions and the potential background seismicity. Full waveform, accounting for the expected spatial, magnitude and focal mechanism distributions and a realistic local crustal model, are combined with real noise recording to produce either event based or continuous synthetic waveforms. The network detection performance is assessed in terms of the magnitude of completeness (Mc) through two different techniques. First, we use an amplitude threshold, taking into the ratio among the maximal amplitude of synthetic waveforms and station-dependent noise levels, for different values of signal-to-noise ratio. The detection probability at each station is estimated for the whole data set and extrapolated to a broader range of magnitude and distances. We estimate an Mc of about 0.55, when considering the distributed network, and can further decrease Mc to 0.45 using arrays techniques. The second approach, taking advantage on an automatic, coherence-based detection algorithm, can lower Mc to ∼ 0.1, at the cost of an increase of false detections. Mc experiences significant changes during day hours, in consequence of strongly varying noise conditions. Moreover, due to the radiation patterns and network geometry, double-couple like sources are better detected than tensile cracks, which may be induced during fracking.