Groundwork for Using Precariously Balanced Rocks to Constrain Seismic Hazard Models in New Zealand

Abstract eng:
We have undertaken a detailed cosmogenic dating study of precariously-balanced rocks (PBRs) in the central Otago province, New Zealand to understand the age and genesis of PBRs to an unprecedented level of detail within the temperate-humid New Zealand environment. Previous PBR studies have been restricted to desert environments. At face value our 10Be dates indicate that the numerous PBRs in the Clyde area of central Otago have been unstable for around 40ka, although previous central Otago-based studies raise the possibility that the ages are apparent and the PBRs are much younger (<10ka). Consideration of these age uncertainties raises the question as to whether the PBRs have experienced multiple large near-field earthquakes on the Dunstan Fault, or no such earthquakes, considering the long recurrence interval of the fault. Resolution of this issue might therefore have significant implications for near-fault motions for the Dunstan Fault. The dating of buried soils at the base of the PBR to resolve the issue is the goal of current efforts.

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