Following the earthquakes in southern cook straight, the GeoNet rapid response team left immediately to place seismometers around the area, to allow more detailed monitoring and get better information with which to model the fault ruptures.

This meant that when the Mag 6.6 occurred, the enhanced array of seismometers was already in place.

Here is a screen shot of the Mag 6.6 Grassmere Earthquake and immediate aftershocks over the following hours:

This GeoNet video gives an idea of the number and locations of aftershocks from the 16th to19th August