People who follow GeoNet on Twitter or who are signed up to receive earthquake email alerts would have seen the reports.
"Two eq at the same time, the system started on the distant event before dismissing that and locating the ChCh event - check the history!" GeoNet tweeted this morning.
According to GeoNet, a magnitude 2.7 quake struck 25km south of Oxford at a depth of 3km at 9.37am, followed by a magnitude 3.7 quake at a depth of 8km in the same location at 10.10am.
GeoNet acknowledged the new automated system, which has been in use for only a few weeks, needed some creases ironed out and apologised for any alarm caused.
"The great thing about our new rapid system SeisComP3 is that initial quake information is out within a few minutes of an event. This tricky thing is that as more data becomes available, the size, location and depth of the event can change.
"Most of the time the changes are small but occasionally the system makes some poor early estimates, and this can lead to large changes in location and magnitude."
GeoNet suggested people look at the website and check the "quake history".
Those marked "caution" have only had a few observations, while those marked "good" and "best" are more reliable.
"We're trying to balance getting quick notifications out rather than wait minutes before letting you know.
"This morning it has led to two earthquakes changing their locations and magnitudes radically - most particularly their magnitudes end up reduced to less heart-stopping levels.
"Today's earthquakes will help us to refine the notifications we send out, and we apologise for any alarm they've caused."
