Back-projection stacking of P- and S-waves to determine location and focal mechanism of microseismic events recorded by a surface array

0472493 - GFÚ 2017 RIV GB eng J - Journal Article
Vlček, J. - Fischer, Tomáš - Vilhelm, J.
Back-projection stacking of P- and S-waves to determine location and focal mechanism of microseismic events recorded by a surface array.
Geophysical Prospecting. Roč. 64, č. 6 (2016), s. 1428-1440. ISSN 0016-8025. E-ISSN 1365-2478
Institutional support: RVO:67985530
Keywords : microseismic monitoring * back-projection stacking * hypocenter location * focal mechanism inversion
Subject RIV: DC - Siesmology, Volcanology, Earth Structure
Impact factor: 1.846, year: 2016

We present an automatic method of processing microseismic data acquired at the surface by a star-like array. The back-projection approach allows successive determination of the hypocenter position of each event andof its focal mechanisms. One-component vertical geophone groups and three-component accelerometers are employed to monitor both P- and S-waves. Hypocenter coordinates are determined in a grid by back-projection stacking of theshort-time-average-to-long-time-average ratio of absolute amplitudes at vertical components and polarization norm derived from horizontal components ofthe P- and S-waves, respectively.To make the location process more efficient, calculation is started with a coarse grid and zoomed to the optimum hypocenter using an oct-tree algorithm. Thefocal mechanism is then determined by stacking the vertical component seismograms corrected for the theoretical P-wave polarity of the focal mechanism. The mechanism is resolved in the coordinate space of strike, dip, and rake angles. The method is tested on 34 selected events of adataset ofhydraulic fracture monitoring of a shale gas play in North America. It was found that, by including S-waves, the vertical accuracy of locations improved by a factor of two and is equal to approximately the horizontal location error. A twofold enhancement of horizontal location accuracy is achieved if a denser array of geophone groups is used instead of the sparse array of three-component seismometers. The determined focal mechanisms are similar to those obtained by other methods applied to the same dataset.
Permanent Link: http://hdl.handle.net/11104/0269797