**5. Conclusions**

Our results show an intriguing mix of promise and indication of challenges to be overcome. The results are promising in that the spectrum of the arrival times indeed undergoes a blue shift, the nature of which is notionally able to discern between the main localized, omnidirectional propagation stage and the period during which the propagation was arrested except, perhaps, for some slow growth that was directionally limited but during which most of the events were being generated from apparently spatially random locations around the vicinity of the fracture surface. What's more, the blue shift can be characterized by a parameter, the localisation exponent, which can theoretically be tied to the dimensionality of the leading edge of the hydraulic fracture.

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However, we also discovered a preponderance of events that emit from the vicinity of the already-fractured surface rather than being localized at the leading edge. The impact of these non-localized events remains a topic for ongoing investigation. Hence, our ongoing work is aimed at providing a clear understanding of how experimentally derived values of the localisation exponent can be used to predict the fracture pattern associated with a given sequence of events.
