Kaikoura refines hazards
The first research paper based on data from last November's Kaikoura earthquake has made a splash with its publication
in high-profile journalScience.
Image: a radar interferogram mapping deformation from the earthquake - each colour contour shows 50cm of vertical
displacement towards or away from the satellite. Supplied, GNS Science.
With 29 co-authors from 11 national and international institutes, this morning's publication presented data from the magnitude 7.8 earthquake including satellite radar imagery.
The authors say the November earthquake was so complex and unusual, it's likely to change the way scientists think about
hazards in plate boundary zones worldwide.
The study, led by GNS Science, showed that at least 12 major crustal faults ruptured during the earthquake, plus another
nine lesser faults. There was also evidence of slip along the southern end of the Hikurangi subduction zone plate
boundary.
Some of the faults that ruptured were thought to be isolated, but the shaking 'jumped' between faults, in one case by
more than 15 kilometres. While it isn't the first earthquake to rupture multiple faults that were considered isolated -
the 2011 Tohoku earthquake was a larger magnitude than expected for that reason - Kaikoura provides dramatic evidence
that a rethink of hazards may be necessary.
"I think it's a wake-up call," US seismologist Ned Field told Science. He leads the team modelling California's seismic hazard and recently upgraded the likelihood of a large quake in the
state based on the phenomenon of multiple faults rupturing in a single tremor.
GNS Science geodesy specialist Dr Ian Hamling led the study - the first of an estimated 10 papers currently being worked on by GNS staff.
He said the complex and lengthy nature of the rupture hampered early attempts to accurately determine the magnitude of
the earthquake, which could pose issues for early warning systems.
Dr Hamling said the earthquake had underlined that conventional seismic hazard models were too simple and restrictive.
“The message from Kaikoura is that earthquake science should be more open to a wider range of possibilities when rupture
propagation models are being developed.”
University of Melbourne's Associate Professor Mark Quigley said the seismic hazard of an area was typically based on the magnitude of mapped faults independently. "Recently we have
begun to consider the statistical probability of earthquake ruptures to ‘jump’ across from one fault to the next with
more sophistication."
"This study will become a classical example of a complex interplate earthquake and will stimulate earthquake research
for decades," he said.
University of Pennsylvania's Professor Kevin Furlong said the geography of this region of the Australia-Pacific plate
boundary meant the area that ruptured was beneath land, "more typically the ruptures are offshore".
"As a result, the surface faulting that is able to be so well documented in the Kaikoura region is usually invisible (if
it occurs) in other large megathrust earthquakes. This and some other studies focused on the rupture behaviour of the
upper crust provide for the first time direct observations of such deformational behaviour."
The SMC gathered expert reaction on the study.