Monday morning’s M7.8 earthquake near Kaikoura has caused massive permanent displacement of the land in the northern half of the South Island (GeoNet Story on Coastal Uplift). Detailed knowledge of these land displacements provide us with critical clues to help determine which faults ruptured during the earthquake, and how much movement occurred on them. Although many GNS and GeoNet scientists are currently “on the ground” trying to obtain information about the earthquakes and its impacts, sometimes we can get an even better picture of what happened in the earthquake by stepping back and viewing it from space.
To do this, we must turn to specialized satellites that collect radar data that can be used to track these land movements in great detail. A technique called InSAR, which stands for ‘Interferometric Synthetic Aperture Radar’, utilises radar satellites orbiting ~700 km above the earth to precisely measure the distance between the ground and the satellite. If the ground moves between two subsequent satellite passes, due to an earthquake or volcanic eruption, then the distance between the ground and the satellite changes. Observing these changes in the positon of the land with InSAR enables us to generate detailed maps of ground movement, often with centimeter-level accuracy.
The InSAR images that have been coming out from the European and Japanese satellites are astonishing, and give us the most detailed view yet of what happened in the M 7.8 quake. The satellite images reveal huge changes in land movement across the Hope and Kekerengu faults, as well as several other faults in the region. To the east of these faults, the land went mostly southwest (see blue area in the figure on the left). In contrast, to the west of these faults the land moved mostly northeastwards (see red area in figure on left). Sharp changes in land movement are visible on the InSAR images, and show us where the faults ruptured to the Earth’s surface.
The satellite images clearly show that Monday’s M7.8 earthquake is one of the most complex earthquakes that has ever been observed. Consistent with observations from geologists of fault displacements on the ground, the InSAR results suggest that the earthquake ruptured at least four different faults, and probably more. The biggest displacements are seen on the Kekerengu, Hope, Hundalee, and Papatea faults.
Scientists at GNS have done computer simulations to replicate the ground displacements observed by the satellites and GPS measurements (GeoNet Story on GPS). To fit the InSAR and GPS displacement data, the computer simulations require up to 10 metres of slip across the Kekerengu fault north of Kaikoura. Our scientists are working hard to pull all of the details that they can out of these exciting and important satellite images to better inform our understanding of what happened in the massive quake.
A perspective 3-D view towards the east coast of the South Island of the results from the computer simulation to determine the amount of movement on faults in the earthquake. The model shown fits the InSAR and GPS displacements well. The faults are shown as a mesh of rectangles. The colors show the amount of slip on the faults in the model (in meters). Some portions of the faults (representing the Kekerengu fault) accommodated up to 10 metres of slip
Contact Scientist: Ian Hamling, email@example.com