Shear-tensile/implosion source model vs. moment tensor: benefit in single-azimuth monitoring. Cotton Valley set-up.

Moment tensor (MT) has become a standard for description of seismic sources, both in earthquake seismology and for various types of induced seismicity. It is a general dipole source, but for practice it may be too general, its generality causing troubles during its reconstruction from noisy data in the inverse process, which may be additionally ill-conditioned due to inexact hypocenter location or availability of a rough velocity/attenuation model only. Then, the retrieved source may be biased. It seems reasonable to assume a simpler and intuitivelly more physical source model directly describing the physical phenomena anticipated in the particular focus. A simple combination of a shear slip with tensile crack or 1D implosion (STI) may be a good model both for natural earthquakes and induced events. The model simplification introduced is crucial in cases of depleted sensor configuration when the moment tensor fails, in single-azimuth monitoring in particular. This is just the case of application in oil and gas industry, where the monitoring of seismicity induced by hydrofracturing is typically performed from single monitoring borehole. Then, MT is able to provide constrained solutions only (e.g. deviatoric), but STI detects also non-shear component correctly, providing important information on increase of permeability of the reservoir.