Updates

The Tephra Seismites team has had a busy month, with successful field campaigns conducting ground-penetrating radar (GPR) at Rotoroa/Hamilton Lake with Dr Andrew Lorrey and John-Mark Woolley (NIWA), and sediment coring at seven Hamilton Basin lakes with Dr Marcus Vandergoes and Henry Gard (Lakes380 and GNS Science).

This follows fieldwork with Dr Pilar Villamor and Genevieve Coffey (GNS Science) in February to continue investigating Te Puninga Fault, also using GPR.

Thank you to our collaborators, and all those who helped with fieldwork permission and access.

Join the upcoming NZGS Webinar presented by Max Kluger, who will provide an overview about newest findings from the Tephra-Seismites project.

The webinar will take place on 28th March 12:30PM to 1:30PM. Registration is free an can be made at https://www.engineeringnz.org/courses-events/event/hamiltons-seismic-hazard/

While we plan for fieldwork later this summer, some of our team members have also been busy in the lab with triaxial testing to characterise the mechanical properties of pumiceous sands and tephras. These tests will tell us more about the conditions under which the tephras in our lake cores have liquefied.

In recognition of having submitted the first of our papers from the project, and a lot of hard work thus far, our group and supporters met for a special lunch last Friday (13 Aug).

Triaxial tests in the lab, led by Danche, got underway earlier this week – though these are now on hold with the latest lockdown! There is plenty to do from home, however. The team are working on abstracts for the forthcoming Geoscience Society of NZ annual conference at Massey University (Palmerston North) later this year, and on the first report to our Marsden funders. As we head into spring, we are also looking forward to resuming our fieldwork.

Our first newsletter update on research progress went out to colleagues and stakeholders this month. A copy can be found below.

Last week we also had a visit from Auckland-based team member Professor Rolando Orense for our first in-person meeting, before he gave a New Zealand Geotechnical Society presentation.

Late last month, the Tephra Seismites team went to visit one of our field sites and collect tephra samples for lab testing, to better understand how and why they might liquefy in an earthquake.

We found Tuhua (Mayor Island) tephra (7.6 cal ka) and Mamaku tephra from the Okataina caldera (8.0 cal ka), which are the upper and lower tephras respectively in the photo below. Jordanka will be using these in her geomechanical tests.

We are looking for a doctoral student to join our team, for a project on characterising and using liquefied lacustrine tephra layers to evaluate paleoearthquakes and seismic hazard in the Hamilton lowlands.

The PhD project will involve (1) lake coring; (2) interpreting CT and micro-CT images of liquefaction of tephra layers in lake cores; (3) developing methods to characterise the liquefied tephra layers (tephra seismites) quantitatively in 3D (geometric morphometrics); (4) analysing spatial patterns of the seismites; and (5) evaluating paleoseismicity and hazards in and beyond Hamilton.

More information is available through the University of Waikato website here.

From the week beginning 15 February, 2021, we have been taking part in a joint project investigating the newly discovered Te Puninga Fault near Morrinsville. This fault is the closest to the Hamilton Basin and so we are trying to work out if activity on the Te Puninga Fault may have impacted on Hamilton Basin, where we suggest the liquefaction of lacustrine tephra layers (tephra seismites) has been caused largely by activity on one or more of the local Hamilton Basin faults. By studying the Te Puninga Fault we plan to test this idea.

The work on the Te Puninga Fault is jointly funded by an EQC project entitled “Paleoseismology of the newly discovered Te Puninga Fault, Hauraki Plains”, and our Marsden Fund project associated with paleoseismicity of the Hamilton lowlands.

Directed by palaeoseismologist Dr Pilar Villamor (GNS Science), three large trenches were opened on two different strands of the fault scarp that runs essentially north-south (roughly parallel to SH 27) a few kilometres to the northeast of Morrinsville. Others involved in the trenching work included Drs Kelvin Berryman and Kate Clark (GNS Science) along with Waikato-based geoscientists David Lowe, Vicki Moon, Alan Hogg, and Joshua Hughes. Joshua has joined the tephra seismites team to work on the Te Puninga Fault as part of his University of Waikato graduate studies (2021-22).

The fault and trenching made national news coverage including the entire front page of the Waikato Times (19 Feb 2021) and TV news items including Joshua speaking on One News. See the following links for more: Stuff news;
this video, and this article in Newshub.

This week we analysed the internal structure of the sediment cores we collected at Rotoroa, Rotokaeo, and Waiwhakareke using a medical CT scanner at Hamilton Radiology. This method provides a first estimation about whether or not seismites (tephras deformed by earthquake activity) are present in the sedimentary record. Next week we plan to cut the cores lengthwise for detailed sediment description and sampling.