Liquefied volcanic-ash layers (‘tephra seismites’) preserved in lake sediments have never been reported. In northern New Zealand we have identified at least four such seismites in tephra-bearing lakes aged ~20,000 years in the Hamilton Basin.
Our aim is to use this unique opportunity to develop a novel methodology to evaluate the reccurrence time, possible magnitude, and likely locations of major earthquakes for the past 20,000 years in the basin via four objectives:
- We will map the seismites spatially and temporally,
- measure their properties,
- develop a mechanism for their generation, and
- assess seismic risk.
To attain these objectives, we will use interdisciplinary techniques including tephrochronology (to obtain accurate, precise ages on the tephras); CT imaging and physical and geotechnical analyses to characterise the seismites; and cyclic triaxial testing to develop a cyclic resistance model. From the model we will derive minimal paleoseismic intensities that initiated the liquefaction in the tephra seismites, and hence generate paleoseismicity and earthquake-risk maps. This approach to paleoseismicity could be applied elsewhere in New Zealand, and globally, to help date activity on hidden faults in low-moderate seismicity volcanic regions where faults and tephra seismites occur.