Science Response to the Valentine’s Day Earthquake: Space data, GPS, and drones

On Sunday, a magnitude 5.7 earthquake struck offshore from Christchurch. Once the ground stopped shaking, our science response kicked into high gear. We are throwing all the science we got at this newest member of the family of large earthquakes in Canterbury. Our scientists have been spending the week running models, gathering data (some of it from space) to look at the Valentine's Day quake in-depth. We got an enormous amount of information from this quake and we are still making sense of all it.

First off the block, we determined that the location needed further refinement. Our best seismologists and geodesists have been hot on the case, each of them using a slightly different way to look at the quake, including data from our GPS and data from space (InSAR).

We now have a more exact location and depth for this earthquake. It is closer to shore (2 kilometres away) and shallower (8 kilometres instead of 15) than our initial review [see image]. The magnitude is still the same. This shift in location better aligns with the accelerations that were recorded, as well as the extent of the liquefaction activity and rockfalls. 

Investigating the Earthquake

Our group of scientists have taken extraordinary measures already, individually and as a team, to learn as much as we can as quickly as possible. We know how important it is to people in Canterbury to provide the fastest and most robust information we can about these quakes. Here's our scientists talking about how they go about their contributions to understanding this new chapter of earthquakes in Canterbury:

Our Scientists:

Dr Sigrun Hreinsdottir - GPS

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A.When you have an earthquake the whole surroundings move. We take measurements from continuously running GPS stations which record how the earth moved at the surface. From that information we can infer how the fault moved under the earth during the quake, as well as pinpoint where the earthquake happened. This is completely independent from how the seismologists calculate the same parameters. Additional stations are occupied and measured every year in Christchurch, and this annual campaign had just wrapped up when the earthquake struck. They were therefore able to go out again and take measurements days following the quake to record how each station has moved as a result of the quake.

 

Q. How does this research compare to what you could do five years ago?
A. Before the Canterbury earthquake sequence, we had  fewer continuous GPS stations. We try to cover all of New Zealand, so the emphasis has been on the regions that are most active. In response to the 2010 and 2011 earthquakes, the network around Canterbury has grown to gather as much data as we can.

Dr Ian Hamling - InSAR

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A. At the moment I'm taking the measurements from 13 GPS stations around the earthquake, and using them to generate a model that can recreate movements at the earth's surface. That will then give us an idea of the size of the fault that moved and how much it moved by. 

I'm also using data retrieved from space. This is called InSAR data, gathered from satellites in orbit. Every time the satellite passes over New Zealand it sends out pulses of radar energy. These pulses bounce off the earth's surface and are recollected by the satellite and put together as an image over the region. Changes in images before and after Valentine's Day would be caused by the earthquake. The Valentine's Day earthquake is on the smaller side of what InSAR can detect. At the moment from the preliminary results it looks as if there is a few centimeters movement along the coast which we should be able to detect with the radar measurements.

Q. What other things can InSAR measure?
A. There are loads of things you can do with InSAR. You can monitor earthquakes, volcanoes, subsidence from oil and gas operations. You can also look at geothermal subsidence. I've spent a lot of time on the Taupo Volcanic Zone and the whole region is subsiding 2cm a year. With InSAR you can generate large maps showing deformation over a wide area.

Dr Stephen Bannister - Relationships between the Earthquakes

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A. My work is all about determining the relationships these earthquakes and faults have with each other. We do this by re-examining the earthquakes in relation to each other and compare the earthquake waves from earthquakes that occurred several days or even years apart. We position those earthquakes in relation to each other to understand how the sequence evolves. In this case, the relationship between the aftershocks of this sequence and aftershocks that occurred in June and Dec 2011 as they are all located close to each other. The more we can understand the interrelationship between June and December 2011 and this week's sequence and other events, the more we can comprehend and understand that fault network. That way we can look at and interpret how the various faults are positioned in relation to one another.

Some of these faults may be in the same location as previous ruptures, but slightly deeper and slightly different orientations. So it seems like a very complex fault network and the answers aren't as straight forward as with other earthquake sequences.

Q. How does this research compare to what you could do five years ago?
A. All the approaches that we use are much tighter and more adaptable than what we were doing five years ago. 

Dr Caroline Holden - Strong Motion Data

Q. Tell us about the science that you are doing now based on the Valentine's Day Earthquake?
A. I'm looking at the fault rupture mechanism using very nearby strong motion instruments from GeoNet. We run different models, based on what the GPS is telling us. An earthquake starts at one point on a fault, and the rupture migrates along that fault. The models we run assume different fault orientations, directions of the rupture, and amounts of offset from the earthquake. When a fault breaks the surface, this work is much easier, as you can see the orientation of the fault there on land. But the earthquake needs to be large and shallow for the surface to rupture. Examples of this is the original Darfield magnitude 7.1.

Q. How does this research compare to what you could do five years ago?
A. This is the first time we've had a whole sequence that has been extremely well recorded. We have GPS, and InSAR, and heaps of seismograph stations. Because there are so many more stations now compared to five years ago, we can get better information. We've also learned that Christchurch is incredibly complex due to the variability of the soil. 

 

 

But wait... there's more!

We've made an updated decay curve to show how the Valentine's Day Earthquake has an effect on the overall Canterbury Earthquake sequence:

 

 

We also have a landslide team currently out in the field. They are scanning cliffs with lasers and flying drones around to get a better idea of what's happened due to this quake. When they're back in the office we'll share what they've found. We've also got our liquefaction team, as well as our social scientists assisting with the response. 

So, we are throwing all the science we got at this quake.

Our thank you list

There are many other players that contribute to this science:

  • InSAR images from the Japanese Aerospace Exploration Agency
  • Campaign GPS is carried out by Land Information New Zealand and University of Otago
  • Additional continuous GPS data is provided by companies Trimble (Geosystems network) and Leica (Global Survey)

 

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