Wave equation moment tensor inversion of microseismic events using multiwell distributed acoustic sensing recording

The directional nature of distributed acoustic sensing (DAS) measurements can limit their usefulness for moment tensor estimation, which is traditionally inverted using multicomponent sensors. However, we find that moment tensor inversion using DAS data acquired in a dual-well microseismic monitoring scenario can yield reliable estimations of all moment tensor components. Our approach adapts a linear waveform inversion method, incorporating 3D anisotropic viscoelastic Green’s functions, for use with DAS data. We estimate the moment tensors of 20 microseismic events recorded at the Hydraulic Fracturing Test Site II after relocation and velocity model updates. We observe a very good match between the field data and the synthetic data generated using the inverted moment tensors. Accurate event locations and reasonable velocity models are important for successful moment tensor inversion. The resolution analysis of each moment tensor component, taking into account the influence of the array and the noise-dependent uncertainty, shows that the unidirectional recording of DAS is not a limiting factor for this acquisition geometry. Noise unevenly influences the uncertainty of the different moment tensor components, but most of them remain resolvable for most events, even with low signal-to-noise ratio. We show that the horizontal parts of the array contribute mostly to M_xx, M_yy, and M_xy, whereas the vertical parts are important for M_zz, M_yz, and M_xz. The inversion and resolution analysis methodology is scale independent and can be used to study the moment tensor resolution of alternative acquisition geometries in microseismic monitoring configurations or seismological studies.