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Earthquake timings and fault interactions in central New Zealand.

J.Humphrey, A.Nicol, A.Howell, N. Litchfield, R. Van Dissen, R. Langridge, B.Fry. (2022) Earthquake timings and fault interactions in central New Zealand.. Geoscience Society of New Zealand Annual Conference 2022: Programme & Abstracts Volume. Geoscience Society of New Zealand Miscellaneous Publication 161A. Geoscience Society of New Zealand, Wellington, pp. 88. ISBN (online): 978-0-473-66216-5 ISSN (online): 2230-4495. https://gsnz.org.nz/assets/Uploads/Shop/Products/GSNZ_annual_conference/MP161_2022_Palmerston_North/MP161A_2022_GSNZ_conference_Palmerston_North_Abstract_Volume.pdf


Forecasting the probability and magnitude of future large magnitude earthquakes is typically dependent on information collected from paleoearthquakes. These paleorecords are often incomplete and timing of earthquakes are imprecisely dated, which impacts our ability to estimate their slip and recurrence intervals.

Historical events demonstrate that many large earthquakes rupture multiple faults with complex rupture patterns. To improve understanding of the importance and controlling factors of multi-fault earthquakes, we compare the timing of earthquakes between active faults in central New Zealand. We use a compilation of more than 150 existing radiocarbon dates recalibrated using OxCal V4.4 to determine the timing of earthquakes. Bayesian statistics are applied to test and quantify the probability of earthquake synchroneity between different faults and segments of the same fault. The refined data provides improvements for the timing of paleoearthquakes for the faults studied. These new ages indicate that in some cases, the timings of surface-rupturing earthquakes vary between faults. In other cases, inferred paleoearthquakes on different faults are approximately the same age, suggesting interactions across fault systems. These “synchronous” earthquakes occurred during time windows of up to 150 years, with the most striking event recorded on the Wellington, Wairarapa and subduction thrust faults at approximately 700-850 cal. yrs BP.

The apparent synchroneity of earthquakes could indicate the occurrence of large multi-fault ruptures and/or earthquake clusters, both of which may suggest stress transfer and interactions between faults on timescales of seconds to hundreds of years. These fault interactions have important implications for seismic hazard in central New Zealand and will be used to inform physics-based earthquake modelling.

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