We are changing how we report earthquakes off-shore Bay of Plenty

Published: Mon Nov 6 2017 3:45 PM

Last week we learnt a lesson about how we report the location of earthquakes. As a result, we are in the process of modifying the way our automated system reports an earthquake in the Bay of Plenty region.

When we set up our automated earthquake reporting system, we spent some time thinking about the key information to include. The idea was to report on who an earthquake is most likely to have affected and how they may be affected. In addition to the magnitude, depth and time, it’s the location of the earthquake that give context. So to accurately locate an earthquake, our system selects the closest geographical landmark and processes the information into an earthquake report.

We covered this briefly in the news stories we posted last week, about the series of small-moderate sized earthquakes that were occurring off-shore in the Bay of Plenty region. These were near but not at White Island.

These earthquakes were due to tectonic activity and were not volcanic. However, this wasn’t very clear in our earthquake reports. The nearest geographical location for our earthquake report was White Island, but reporting this led people to believe that these earthquakes were related to volcanic activity. Actually, it’s not unusual for earthquakes to occur in the Bay of Plenty region due to the active regional fault system that extends off-shore northeast of the Bay of Plenty. You can find out more from the regional Civil Defence website.

In the image below, the swarm is quite clear and they do appear close to White Island. Our volcanologists here at GeoNet, however, confirmed that they were still too far from White Island to be related to volcanic activity.

This is an image of all the earthquakes that have occurred near White Island (pink triangle). Last week's swarm is visible and although the swarm is near White Island, these earthquakes are not due to any volcanic activity.

This is an image of all the earthquakes that have occurred near White Island (pink triangle). Last week's swarm is visible and although the swarm is near White Island, these earthquakes are not due to any volcanic activity.

Additionally, the reports from these earthquakes were not providing relevant context in terms of who these earthquakes were affecting (no-one lives on White Island). So, to avoid this confusion we have decided to not report the location of Bay of Plenty earthquakes in relation to White Island. We already apply this rule to the earthquakes we record near our other volcanoes such as, Ruapehu or Taranaki.

We hope that with this fix, we will improve the way we report earthquakes to you. It’s not a substantial change, but a change nonetheless - and you will still receive notifications of earthquakes.