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The ability to detect aligned fractures using seismic anisotropy provides a valuable tool for exploiting hydrocarbon reservoirs better. Perhaps the most direct way of identifying anisotropy is by observing shear wave splitting. However, the interaction of shear waves with subsurface structure is often complicated. Although fractures in hydrocarbon reservoirs are usually subvertical, shear waves recorded on downhole receivers from microseismic events in or near the reservoir are not likely to have travelled vertically. As such, interpreting splitting measurements made on such waves is a non-trivial problem. Here we develop an approach to model the effects of subsurface structure on non-vertically propagating shear waves. Rock physics theory is used to model the effects of sedimentary fabrics as well as fractures, allowing us to use shear wave splitting measurements to invert for aligned fractures. We use synthetic examples to demonstrate how it is possible to assess in advance how well splitting measurements will image structures, and how this is highly dependent on the available range of ray coverage. Finally, we demonstrate the inversion technique on a passive seismic data set collected during hydraulic fracture stimulation. Despite an unfavourable source–receiver geometry, the strike of an aligned fracture set is accurately identified. [ABSTRACT FROM AUTHOR]

The Siberian traps rank among the largest flood basalt provinces in the world. Major magmatic activity is restricted to several short periods of less than 1 Myr around the Permo-Triassic boundary. We measured the anisotropy of magnetic susceptibility (AMS) of 183 basaltic samples from 28 individual lava flows belonging to the northwestern part of the flood basalt province, in order to test the reliability of such data in structural interpretation. These preliminary AMS data show a remarkably consistent pattern of magnetic lineations, that likely reflect the primary flow-related texture of the basalt. Our results also emphasize that AMS data are consistent with the well-documented petrological and geochronological data. The inferred flow directions are also consistent with flow directions expected from isopach maps. Our results suggest that the entire 2 km-thick lava pile was fed by fissure eruptions located in the rifted basin that bound the Siberian platform, and was controlled by topographical features, particularly major rift zones. [ABSTRACT FROM AUTHOR]