Photo Caption:鶹ý Geology PhD graduate Jade Humphrey taking samples from a trench dug on the Hope Fault near Kaikōura.
Jade Humphrey, who has just completed her PhD in Geology from Te Whare Wānanga o Waitaha | 鶹ý (UC), used paleoseismic (geological) methods and historical records to review the timings of major earthquakes along the Wairarapa, Wellington, Ōhāriu and Hikurangi subduction zone.
The data, exploring the timing of magnitude 7 and larger quakes, spanned about 5,500 years.
Dr Humphrey says the findings suggest about two-thirds of the large magnitude earthquakes along lower North Island faults are clustered in time, pointing to interactions between the faults.
“Our results highlight that many of the faults studied in the Wellington region ruptured quite recently, just prior to European arrival. In Wairarapa, a well-known fault ruptured in 1855, and the Wellington and Ōhāriu faults ruptured just prior to the Wairarapa fault. So, there was a cluster of earthquakes around 200 years ago, which is consistent with the faults rupturing together or in close sequences.
“However, we can’t say for sure whether the earthquakes on these different faults are happening within days, months or years of one another.”
The study was in partnership with Earth Sciences New 鶹ý (formerly GNS Science) and principally funded by Resilience to Nature’s Challenges (RNC2). The results have been published in the .
While the precise causes behind these quake clusters is unclear, Dr Humphrey says a potential implication of this work is that earthquake risk in the Wellington region is “probably time dependent”.
She says where we are in time relative to temporal clusters can make a big difference in terms of risk. “Inside the clusters the hazards are relatively high, and outside potentially much lower.”
Dr Humphrey, who is now a postdoctoral researcher at UC and lecturing in a fourth-year Geology course, says further research she is working on using earthquake simulators will help understand how the faults are linked.
Originally from the Wellington region, Dr Humphrey says growing up in Wainuiomata, she was conscious of earthquake risk.
“I’ve always had a curiosity about how the earth forms. Watching coverage of the Canterbury earthquakes on TV, I wanted to come to Christchurch and learn more about them.
“I arrived in Ōtautahi in 2016, just in time for the magnitude 5.7 Valentine’s Day quake. That was followed by the Kaikōura earthquake in November the same year.
“I’ve had some amazing opportunities to work with a team of earthquake experts in New 鶹ý.”
Dr Humphrey enjoys the paleoseismic work, which involves getting out in the field, digging trenches on faults and removing sediment samples to examine under a microscope for radiocarbon dating.
Samples she has taken north of Kaikōura, on the Hope Fault, revealed evidence of earthquakes up to 12,000 years ago.
Outside of her academic work, Dr Humphrey is also the founder of Predator Free Riccarton, which aims to eradicate introduced pests such as rats and mice through backyard traps in a large area of Christchurch that includes Riccarton Bush.
In this role she works with 10 schools and regularly gives talks in the community.
“I love nature and community connection, so this voluntary work combines both of those aspects,” she says.
Dr Humphrey is joining UC’s Spring Graduation celebration held at Wolfbrook Arena, Christchurch on Tuesday 26 August.
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