This is one of the most complex on-land earthquakes ever recorded – to date, at least 12 faults have been mapped where they have broken through to the ground or sea floor.
Unlike the cracks associated with landslides, these breaks start kilometres down in the crust, and come all the way up to the ground surface, shunting land sideways and upwards. Some fault displacements are just wee steps or small cracks in the ground, while others have produced metres-high cliffs, or land has been pushed sideways by many metres relative to land on the other side of the fault. New Zealand Geographic magazine has a great story about the fault ruptures and the geologists investigating them, with some amazing photos illustrating how the faults have moved.
So far, most of the fault mapping and has been done on foot, or by helicopter or drone. Offshore, NIWA have used a multibeam echosounder and high frequency sub-bottom profiler (fancy machines with interesting names that map the sea floor) on the Tangaroa to detect the movement on the undersea Needles Fault.
The initial field reconnaissance of the faults has now finished, but LiDAR – a type of high-resolution ground mapping – is now being flown over much of the area affected by the earthquake. And early in the new year NIWA scientists will be back out on a smaller boat the Ikatere, which can get closer to shore than the Tangaroa, to map how the onshore and offshore fault ruptures join up.
After taking a well-deserved break over the holidays, the geologists will begin analysing the mountain of data collected, to work out their piece of this earthquake story. It’s likely that once the LiDAR and Ikatere data are analysed even more fault ruptures will be discovered, and they’ll then have a better idea of the total movement that has taken place.
Further down the track they’ll also be looking at the connections and gaps between the faults and what this means for seismic hazard modelling. Is there evidence for these faults having ruptured together before? And is this normal?
We'll update you next year on this research, which gives us a window into understanding not only this earthquake but how New Zealand reshapes itself through earthquakes over millions of years.