Slip rates for the Hyde and Dunstan Faults, southern New Zealand, revealed by cosmogenic radionuclide dating
Mr Jonathan Griffin1,2, Prof. Mark Stirling2, Dr Klaus Wilcken3, Mr David Barrell4, Krista Simon3
1Geoscience Australia, Canberra, Australia, 2University of Otago, Dunedin, New Zealand, 3ANSTO, Sydney, Australia, 4GNS Science, Dunedin, New Zealand
Reverse faulting in Otago, southern New Zealand, accommodates distributed tectonic convergence on the eastern side of the Australia-Pacific plate boundary. Paleoearthquake records from some of the faults in the region show highly variable earthquake recurrence times, and this work is focused on providing longer term context to these records. We use 10Be cosmogenic radionuclide dating of alluvial fan surfaces to characterise late Quaternary slip rates on two significant faults within the system, the Hyde and Dunstan faults. We determine a slip rate of 0.29 mm/yr (0.24 – 0.37 mm/yr at 95% confidence) for the Hyde Fault since 115 ka and a slip rate of 0.17 mm/yr (0.15 – 0.23 mm/yr 95% confidence) for the Dunstan fault since 320 ka. The lower rate for the Dunstan Fault, which has greater total displacement and is closer to the plate boundary, supports a hypothesis of migration of the deformation front eastward from the plate boundary. Both faults show deviations from a constant linear slip rate through time, with slip rates varying by a factor of 2 – 4 over timescales of 15 – 80 kyr. Increases in slip rate are out of phase on the two faults, supporting a hypothesis that strain is shared within the fault system over timescales on the order of 10s – 100s kyr; however, neither fault shows evidence for long periods of seismic quiescence.
Jonathan Griffin works in the Community Safety Branch at Geoscience Australia, with a focus on characterising earthquake sources for earthquake and tsunami hazard assessment. He has recently submitted a PhD at the University of Otago, researching the recurrence of large earthquakes in low seismicity regions. This has involved collecting new paleoearthquake and slip rate data in the Otago region of southern New Zealand, and developing novel statistical approaches for forecasting earthquake rates from these data.