Source and attenuation parameters for induced seismicity in the Crooked Lake Region of Alberta

English Abstract:

From December 2013 to present an ongoing sequence of over 70 small earthquakes (M_w 2-3.5) was detected in the Crooked Lake region, near Fox Creek, Alberta. The event hypocenters and timing correspond closely to hydraulic fracture treatments of oil and gas production wells in the immediate vicinity, suggesting a causal relationship. The events thus provide a unique opportunity to study the seismological characteristics of earthquakes triggered by hydraulic fracturing in this region. We obtain all available seismographic data from Alberta and B.C., including data from the TransAlta/Nanometrics, GSC, CRANE and AGS stations, to obtain a rich library of waveforms at distances from a few tens of km to a few hundred km. All waveforms are processed to obtain instrument-corrected Fourier and response spectra. We compare the moment estimates from inversion to those obtained using a new algorithm for moment magnitude estimation from regional seismographic ground-motion. Distance cutoffs are established for magnitude ranges in order to reduce noise effects of distant stations while maintaining accuracy in the magnitude estimation. We present our results on ground motion attenuation and source spectra for this sequence of events relative to natural earthquakes of similar size.