Earthquake

Click here for info on the 2010/2011 Canterbury earthquakes

 

 

 

What do you want to do?

Report an earthquake

• Look for it in the list of recent earthquakes likely to have been felt and select the Felt it? button.
• If it isn't listed there, fill out a Felt Earthquake Report anyway.

Find out about New Zealand earthquakes

• View a list of the latest recorded earthquakes at GeoNet Quakes.
• View the last 250 earthquakes on the interactive Quake Time Map.
• Read about New Zealand's major Historical Quakes.
• Check out the statistics of how many earthquakes we have in New Zealand.

Find about about significant earthquakes in other parts of the world

• The National Earthquake Information Center (NEIC) of the United States Geological Survey locates all globally significant earthquakes.

GeoNet and Earthquakes

GeoNet uses automatic locations so we can locate and display every earthquake as soon as we receive enough data. Displaying 20,000 earthquakes on the website instead of a couple of thousand has led to changing the layout of the website content. We've done two things - first, we've split recent earthquakes into two streams; All and Felt. As you may guess All is everything that has been located. Felt is earthquakes that might have been felt. Currently we use an algorithm (a set of calculation rules) to determine if an earthquake might have been felt. As soon as we start collecting Felt Reports for GeoNet Rapid we will use those to help create the Felt list. Second, we've presented earthquakes grouped in the major regions around New Zealand. Each region has an All and Felt list of earthquakes. It's useful to remember that a large earthquake in Wellington could appear in the Felt list for Christchurch even though it's outside the Christchurch region.

Other significant events within the greater south-west Pacific region may be detected by our equipment, but we do not routinely locate these as the geometry of our recording network does not allow accurate epicentres and magnitudes to be determined. Details about these earthquakes are available from the United States Geological Survey.

Did you feel an earthquake?

If you have felt an earthquake recently, we would like to know where you were and what happened to you. This information will help us understand how your area might respond in future earthquakes. Your input will be used to make maps of how the intensity of shaking was distributed over the area which felt the earthquake. The questionnaire should only take a few minutes to complete.

How GeoNet Locates Earthquakes

To make rapid locations of earthquakes GeoNet operates a country-wide network of seismic stations that transmit their data to the GeoNet Data Management Centre (DMC) where it is analysed by automated processes. The earthquake is then located by SeisComP3 and information is released onto the Quake website. The seismic stations operated by GeoNet consist of a seismometer and a digitiser. A seismometer is a sensitive instrument that generates a small electrical current in response to ground shaking. The electrical current is then digitised and transmitted continuously to the DMC in real time. This digital recording of ground shaking is the raw data used to make earthquake locations.

The seismic stations are supplemented by a network of strong-motion seismographs, which only transmit data whenever they detect a higher level of shaking, typically from earthquakes that will have been felt by the public. The real-time seismic data is received by the DMC data reception computers located at Avalon (Lower Hutt) and Wairakei (near Taupo) and analysed automatically for possible earthquakes. The computer processes look for ground shaking that is distinct from the normal background activity (such as that caused by weather and oceans) and may be associated with an earthquake.

These occurrences are called detections. If a detection is deemed significant, then the relevant portion of the data is parcelled up and sent to the DMC data analysis computers. They store all the detected earthquake data, grouping the detections from different stations into earthquake data sets. The detections are examined for P (primary) and S (secondary) wave arrivals from the earthquake, and the times of these arrivals are inverted against seismic velocity models for the earth to yield the best location for the event. The magnitude of the earthquake is determined at a station by measuring the maximum amplitude of the seismic signals, and relating them to the distance of the station from the event, together with the characteristics of the seismometer and seismograph. The magnitudes from all available stations are then averaged to give an overall value for the event.

Preliminary information for earthquakes are posted to the Quakes pages soon after their occurrence; this is updated as more data becomes available.

The system also provides locally recorded data from global earthquakes to the International Seismological Centre in the United Kingdom, and preliminary earthquake information to the National Earthquake Information Center, part of the United States Geological Survey responsible for locating major earthquakes worldwide. The waveform data and the located hypocentres are freely available to the worldwide community of researchers through the Applications and Data section of this website.