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.

Distribution of Faults and tephra-seismites’ bearing lakes in the Hamilton lowlands

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:

      1. We will map the seismites spatially and temporally,
      2. measure their properties,
      3. develop a mechanism for their generation, and
      4. 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.

Downward injection structures of liquefied tephra layers