Observations of fault plane solutions for microseismic events are often presented as apparent dip-slip solutions on vertical discontinuities. We propose an alternative explanation for these observations: the mechanism is not "dip-slip" on vertical structures but hydraulic fracture "tip-slip" on the auxiliary plane i.e. horizontal slip on horizontal structures. The reason for the ambiguity is because both the dip-slip and tip-slip mechanism produce the same seismic radiation pattern in the far field.
The intersection of the slip plane and its auxillary for the source mechanism described above, produces a line parallel to the hydraulic fracture plane. This alignment requires the slip vector of such a source to be orthogonal to the hydraulic fracture. This in turn fits with an interpretation of either tip-slip opening or tip-slip closing of the hydraulic fracture.
Such an interpretation would force us to rethink our perception of the relationship between the hydraulic fracture and seismicity, since this would represent a direct link between the opening of the hydraulic fracture and observed seismicity. The mapping of source mechanisms over time would then represent a direct measure of successive opening events and may be tied to hydraulic fracture conductivity.
We present our argument to support this hypothesis of tip-slip motion.
Presentation Date: Tuesday, October 18, 2016
Start Time: 10:45:00 AM
Presentation Type: ORAL